"Smart" position transducer system for elevators

Abstract

 An elevator system employing a micro­processor-based group controller communicating with the cars (3, 4) using car position and velocity information provided by a "smart" primary position trans­ducer (SPPT) system to control the motion of the cars and assign them to handle passenger demands. The SPPT includes an input shaft coupled to a primary encoder disk. Coupled to the shaft through gearing are one or more encoder disks performing the function of turns counting, as well as additional functions. Each disk contains multiple tracks, and each of these tracks is sensed by a sensor, or, alternatively, the SPPT may use two independent sensors per track. It is important to have two essentially independent means of performing the key sensing functions. The read heads of the SPPT are divided into primary and secondary sets with each set used to feed an independent processor. Within each set of sensor signals, cross checks are performed to insure the integrity of the system, which would detect a cracked or broken glass disk. In the electronics of the SPPT system primary and secondary position signals are each found by two methods and compared to maximize the likelihood of correct position determination, with one method given priority over the other, depending on the circumstances. Two independent channels for position and velocity information are main­tained, using independent parts, except for the input shafts and encoder disks. Exemplary formulae for determin­ing and generating the desired primary and secondary position and velocity information are provided.

Description

[0001] The present invention relates to elevator systems and to encoding and locating the position of the elevator cars in an elevator system. More particularly the inven­tion relates to a primary position transducer system for determining the location of an elevator car in an elevator system.

[0002] In an elevator system, one or more cars travel up and down the length of the elevator run, moving between the floors of the building carrying passengers.

[0003] In order to, inter alia, stop smoothly and level with the landing at each floor, it is important to know the precise location of the car at all times. To provide this information to the elevator controller system, a digital readout device known as a Primary Position Trans­ducer or "PPT" is used.

[0004] For mid- and low-rise installations, a reader device mounted on the car and a vertical steel tape that runs the length of the hoistway are used to establish the car's position. Either steel vanes and/or magnets are mounted on the tape at precise locations with respect to the floor level of each landing.

[0005] For an example of a prior art position transducer system used with an elevator system, note our U.S. Patent 4,384,275 entitled "High Resolution and Wide Range Shaft Position Transducer Systems" of Masel et al. In that patent two rotary position transducers are coupled to each other and to the shaft being rotated. Both of the transducers include one or more coded disks having sensing indicia forming tracks thereon that rotate a plurality of times in response to the rotations of the shaft, one of the transducers rotating at a different speed than the other. Each transducer produces signals, which are individual to the respective transducer and are the same for each rotation of the respective transducer.

[0006] The Masel patent includes:
sensing means related to each track for sensing the indicia thereon to provide signals indicative of the rotation of the disk from a rotational reference position; and
signal processing means interconnected to the sensing means responsive to the signals correspond­ing to the coded tracks for providing a binary signal representation of the angular position of the disk and responsive to the signals corresponding to the coded tracks to provide, as a function of the number of coded track indicia which have been sensed indicated thereby, a binary signal representation of the number of revolu­tions that the disk has rotated from the rotational reference position.

[0007] Some additional patents which may be of interest are U.S. Patents 4,041,483 entitled "Absolute Incremental Hybrid Shaft Position Encoder" of Groff issued August 9, 1977; and U.S. Patent 3,885,209 entitled "Two Speed Control Syetem" of Lazarus issued May 20, 1975. In the latter patent first and second transducers are connected to first and second rotatable shafts, respectively, with the shafts coupled to each other through a single mesh of gears. The transducers are electrically coupled in cascade to enable the first to provide a "fine" indica­tion of the angular position of the first shaft, while the second provides a "coarse" indication of the number of revolutions of the same first shaft.

[0008] According to the invention there is provided an elevator system, in which there is at least one elevator car whose speed is controlled by a motion control subsystem and in which there is to be included a transducer system for determining the vertical position of the car in the elevator run by providing a binary representation of the number of revolutions made by a rotatable shaft to which a transducer is connected, which shaft carries a movable encoder element having at least two coded tracks, a fine track and a relatively coarse track, made up of sensible indicia, said transducer system includ­ing:
sensing means related to each track for sensing the indicia thereon to provide signals indicative of the movement of the encoder element from a reference position; and
signal processing means associated with said sensing means responsive to the signals corresponding to the fine coded track and to the relatively coarse coded track for providing a binary signal representation of the relative position of the encoder element and responsive to the signals corresponding to both of the coded tracks to provide, as a function of the number of coded track indicia which have been sensed indicated thereby, a binary signal representation of the total movement the encoder element has moved from the reference position; characterised in that said transducer system further comprises:
independent means for finding at least two independent position and velocity signals, or derivatives of these signals, with an instrument having a single, common input shaft.

[0009] The "smart" primary position transducer ("SPPT") system of the preferred embodiment is a subsystem of the car control syetem for each car for the overall elevator system.

[0010] The SPPT apparatus includes an input shaft coupled to a primary encoder disk. Coupled to the shaft through gearing are one or more encoder disks that perform the function of turns counting, as well as additional functions.

[0011] Each disk contains multiple tracks, and each of these tracks is sensed by a sensor. An alternate sensing means is the use of two or more independent sensors per track. An important aspect of the invention is to have two or more essentially independent means of performing the key sensing functions.

[0012] The read heads of the SPPT can be divided into a primary set and a secondary set. Each set of sensors is used to feed an independent processor. Within each set of sensor signals, cross checks are performed to insure the integrity of the system. For example, a cracked or broken glass disk could be detected.

[0013] As noted, an important aspect of the invention is for the sensors to be independent. Although multiple tracks on multiple disks are preferred, it i.s possible to use, for example, a single disk with a sufficient number of tracks, if multiple sensors are included with the single disk.

[0014] The sensible indicia are preferably in the form of optical tracks, although magnetic sensing or hole sensing, etc., could be used. Also, the principles of the invention can be realized in a multi-winding resolver system, etc., and, hence, the use of a disk, although preferable, is not mandatory to the invention.

[0015] In essence the present invention provides means for finding two or more independent position and velocity signals and derivatives of these signals with an instru­ment having a common input shaft. There are many possible embodiments to do this, including for example:

1. An incremental system using a single encoder disk and two or more read heads.

2. A quasi-absolute system using differen­tial gearing that is capable of two independent position and speed signals.

3. An absolute system, including a main disk attached to said input shaft; additional absolute encoders coupled to the input shaft through gears deter­mining the turns of the main shaft; and at least two independent position and velocity output signals being obtained with the use of independent sets of read heads located circumferentially about each disk, a primary output signal being used to run the elevator and the other, secondary, output signal being used for normal terminal protection for the elevator car travel. A combination of the primary and secondary velocity signals may be used to derive a door zone speed check signal in compliance with the ANSI A-17.1 Elevator Code, which requires that an independent means be used to check speed in the door zone. By equipping the system with a third set of sensors, it is possible to obtain an independent position signal useful for verifying that the elevator is in the door zone before the doors are opened.

[0016] By the use of additional sensor assemblies, a fourth independent set of position and velocity informa­tion could be generated for the purpose of meeting the emergency terminal stopping requirements of the A-17.1 code.

[0017] Each set of sensors needs to work with an inde­pendent processor system. In situations where a compos­ite signal is produced from two processors, such as for the door speed check signal, it is essential to buffer the connections from the processors to the common circuitry, so that a failure in one processor cannot affect the operation of the other.

[0018] The basic concept followed in this new class of instruments is to provide independent signals when a common input shaft is used. One interpretation of independence is that a failure in one channel cannot affect any other channel. To guard against a disk fracture, etc., affecting two or more channels, the "health" of each channel is monitored. Any severe malfunction on one channel will cause an emergency stop of the elevator. Also, the system receiving the primary and secondary signals will initiate an emergency stop, if excessive disagreement exists between the primary and secondary channels.

[0019] Thus, the primary and secondary position channels are made independent of one another in the SPPT of the present invention. The sensor devices, such as photo­transistors or coils, used for the primary and secondary position determinations are made independent of each other. With the approach(es) of the present invention a failure in one of the sensor devices will not cause a failure in any other sensor device.

[0020] The "health" of the disks used for quasi-absolute encoding are checked by checking the symmetry of the coarse tracks.

[0021] Absolutely encoded disks are usually encoded using the "Gray" code, and errors can be detected if more than a single bit changes at one time. Also, in abso­lutely encoded systems the turns counting encoders can be used for safety checking.

[0022] In the preferred embodiment the "smart" primary position transducer system is driven by, for example, a steel selector tape attached to the elevator car, using a quasi-absolute transducing system preferably with battery backup. In each transducer, primary and second­ary position signals preferably are each found by two methods and compared to maximize the likelihood of correct position determination.

[0023] The "smart" aspects of the PPT additionally use two independent channels for position and velocity information for the car with which it is associated.

[0024] The SPPT includes preferably two encoders coupled by, for example, "256:257" gearing. The encoders preferably are of identical design, and in the preferred embodiment contain two fine (1024 ppr) tracks, and two coarse (1 ppr) tracks. Each pair of tracks produce signals that are in quadrature with each other.

[0025] The directly-driven encoder is termed the "prima­ry encoder" and is connected directly to an appropriately toothed gear, for example, a two hundred and fifty-six (256) tooth gear. The other encoder is termed the "secondary encoder" and is connected to the primary encoder by means of a different toothed gear, for example, a two hundred and fifty-seven (257) tooth gear. The difference in the number of teeth in the gears used for the otherwise identical two transducers produces a non-"1:1" ratio, namely in the preceding example, a "257/256" ratio of secondary to primary.

[0026] The main and quadrature fine track signals are processed by external circuitry, well known to those of ordinary skill in the art. This processing results in a "x4" (four times) frequency multiplication, and a determination of the direction of rotation.

[0027] The exemplary encoder disks used with the trans­ducer have a range of an exemplary two hundred and fifty six (256) revolutions with, for example, twelve (12) bit per revolution encoding on the primary channel and, for example, at least eight (8) bit per revolution encoding on the secondary channel.

[0028] The two channels preferably use independent parts except, for example, the input shaft and encoder disks. This leads to very high reliability and a very low proba­bility of any undetected failures.

[0029] This two channel integrated elevator position/ve­locity transducer system provides economical performance of the following important elevator control functions:
■ normal position control;
■ normal terminal protection; and
■ door zone protection.

[0030] Signals representing the position and velocity of the respective car may be determined and generated in the following manner:

[0031] The determination of position for the primary channel requires the finding of coarse position and then adding incrementally derived fine positions to it. Further, for reasons of elevator safety, a redundant secondary position is desired. This is accomplished using hardware that is independent of that used for the primary position.

[0032] Primary position as a HEX number consists of:
PRI_POS = COARSE_PRI_POS * 1000 + FINE_PRI_POS
where FINE_PRI_POS is derived from the XY counts and equals "000" at the end of each coarse primary position determination cycle; where the fine track of the primary encoder is "X", the quadrature track is "Y", and the times four ("x4") composite signal is called "XY".

[0033] Two basic techniques exist for determination of primary position (PRI_POS) [as well as for the secondary position (SEC_POS)], once the transducer system is initialized.

[0034] The first technique is to update the coarse position based upon the fine position. When FINE_PRI_POS = 1000, the coarse position is incremented by one count and FINE_PRI_POS is reset to be equal to "000". More, generally, FINE_PRI_POS is divided by "1000" and the result is added to COARSE_PRI_POS, and FINE_PRI_POS is reset to the local remainder.

[0035] If FINE_PRI_POS goes negative, COARSE_PRI_POS should be decremented and FINE_PRI_POS reset accordingly. On an interim basis, the fine position should always be characterized by a magnitude and sign. When the reckon­ing for position is complete, then the fine position is always a positive number.

[0036] The second technique or method is to update the coarse position directly by measurement based on coarse track readings. To do this FINE_PRI_POS is set equal to the appropriate value immediately after the completion of the update.

[0037] The absolute primary velocity (HEX) is computed from the PRIMARY POSITION. Thus:
ABS_PRI_VEL(N)=
[ PRI_POS(N-1)-PRI_POS(N-2) /1000] * (60/T)_HEX
where T = cycle time, which is measured in decimal seconds.

[0038] The secondary position as a HEX number consists of:
SEC_POS =
(COARSE_SEC_POS*1000 + SEC_FINE_POS) * (101/100)_HEX
where SEC_FINE_POS is derived from JK counts, and SEC_FINE_POS=000 at the end of each coarse secondary position determination cycle; where the fine track of the secondary encoder is "J", the quadrature track is "K" and the times four ("x4") composite signal is called "JK".

[0039] The first method is to update the coarse position based upon the fine position. When SEC_FINE_POS=FF0, the coarse position is incremented by one count and SEC_FINE_POS is reset to "000". More generally, SEC_FINE_POS is divided by "FF0" and the result is added to COARSE_SEC_POS, and SEC_FINE_POS is reset to the local remainder.

[0040] If SEC_FINE_POS goes negative, COURSE_SEC_POS should be decremented, and SEC_FINE_POS reset accordingly. On an interim basis, fine position should always be charac­ terized by a magnitude and sign. When the reckoning for position is complete, then the fine position is always a positive number.

[0041] The second method is to update the coarse posi­tion directly by measurement. SEC_FINE_POS is set to be equal to an appropriate value immediately after comple­tion of the update.

[0042] In like fashion for PRI_POS, the first method should always be used. The second method should be used whenever there are no direction reversals during the measurement process. Likewise, for both PRI_POS and SEC_POS, appropriate "disagreement" rules (explained more fully below) are used to maintain the integrity of the data.

[0043] The absolute secondary velocity (HEX) is computed from the SECONDARY POSITION. Thus:
ABS_SEC_VEL(N)=
[ SEC_POS(N-1)-SEC_POS(N-2) /1000] * (60/T)_HEX
where T = cycle time, which is measured in decimal seconds.

[0044] Polarity reversal is necessary as a practical matter to meet different transducer mounting situations. This may be accomplished by the following algorithms expressed in HEX (2's complement):
PRI_POS = 100000 - PRI_POS
SEC_POS = 100000 - SEC_POS
The primary velocity and the secondary velocity given above in the calculation subsection must be reversed when a polarity reversal is indicated. This can be done by changing the sign bit.

[0045] A speed check signal preferably is provided in association with the transducer system for door-zone safety check. The software used preferably stresses fault discovery and automatic recovery, and two indepen­dent serial links (e.g. RS-422 type) preferably are used to facilitate connection of the transducer system to the elevator controller system.

[0046] A discrete speed check signal is provided to indicate that the speed (the magnitude of velocity) is below a prescribed threshold called the speed check. This signal goes "high " whenever both the primary and secondary speeds are below the threshold speed. Other­wise, the signal is "low ". It becomes active within, for example, one hundred (100 ms) milliseconds after power is applied to the transducer.

[0047] It is possible to set two check speeds in the range of, for example, eight to sixty-four (8-64 rpm) revolutions per minute in an EPROM as contract variables. The factory setting for the threshold can be, for example, 27.38 rpm (which is 145 fpm with a 20.231" diameter sheave). By means of jumpers one can choose an alternative check speed of, for example, 17.94 rpm (95 fpm). The speed check signals should be accurate to within at least ± 1.5 rpm and include, for example, a half (0.5) rpm of hystere­sis.

[0048] With battery backup, position information is remembered for, for example, at least one hour after building power failure. The data is updated in memory preferably at least, for example, every ten (10ms.) milliseconds.

[0049] The primary advantages of the invention are its safety, reliability, exceptionally high resolution and accuracy, serviceability, and relatively moderate installation cost.

[0050] The invention may be practised in a wide variety of elevator systems, utilizing known technology in the light of the teachings of the invention, which are discussed in detail hereafter.

[0051] Other features and advantages will be apparent from the specification and claims and from the accompanying drawings, which illustrate an exemplary embodiment of the invention.

Brief Description of Drawings

[0052] 

Figure 1 is a simplified diagram, partially broken away, of an exemplary elevator system in which the exempla­ry embodiment of the smart position transducer system of the present invention may be incorporated;

Figure 2 is a simplified, schematic block diagram of an exemplary car controller, which may be employed in the system of Figure 1, and in which the invention may be implemented.

Figure 3 is a simplified block diagram showing the interfacing of the motion control subsystem (MCSS) for the elevator car with its various related subsystems, including the exemplary "smart" primary position transducer's central processing unit (SPPT-CPU) and the primary position trans­ducer (PPT) of the present invention.

Figure 4 is a schematic diagram providing the circuit detail for the buffered comparator shown in Figure 6, which provides the speed check function of the present invention.

Figure 5 is a functional block diagram of the "smart" primary position transducer circuit board assembly (SPPT CBA) of the exemplary embodiment of the present invention, showing the interfacing of its various elements through the Address, Data buses and I/O ports.

Figure 6 is a simplified block diagram of the exemplary electronic system for the "smart" primary position transducer (SPPT) of the present invention, the circuit detail for the buffered comparator of which is shown in Figure 4.

Figure 7 is a simplified, electro-mechanical block diagram of an exemplary SPPT using absolute encoders.

[0053] For the purposes of detailing an exemplary applica­tion of the present invention, reference is made to our U.S. Patent 4,363,381.

[0054] The preferred application for the present invention is in an elevator control system employing a micro-proces­sor-based group controller dispatcher using signal process­ing means, which communicates with the cars of the elevator system to determine the conditions of the cars, particular­ly their vertical positions in the building, and, for example, responds to hall calls registered at a plurality of landings in the building serviced by the cars under the control of the group controller.

[0055] It is noted that Figures 1 & 2 hereof are substan­tively identical to the same figures of the '381 patent. For the sake of brevity the elements of Figures 1 & 2 are merely outlined or generally described below while any further, desired operational detail can be obtained from the '381 patent, as well as other of our prior patents.

[0056] In Figure 1, a plurality of exemplary hoistways, HOISTWAY "A" 1 and HOISTWAY "F" 2 are illustrated, the remainder not being shown for simplicity purposes. In each hoistway, an elevator car or cab 3, 4 is guided for vertical movement on rails (not shown).

[0057] Each car is suspended on a steel cable 5, 6, that is driven in either direction or held in a fixed position by a drive sheave/motor/brake assembly 7, 8, and guided by an idler or return sheave 9, 10 in the well of the hoist­ way. The cable 5, 6 normally also carries a counterweight 11, 12, which is typically equal to approximately the weight of the cab when it is carrying half of its permissi­ble load.

[0058] Each cab 3, 4 is connected by a traveling cable 13, 14 to a corresponding car controller 15, 16, which is typically located in a machine room at the head of the hoistways. The car controllers 15, 16 provide operation and motion control to the cabs, as is known in the art.

[0059] In the case of multi-car elevator systems, it has long been common to provide a group controller 17, which receives up and down hall calls registered on hall call buttons 18-20 on the floors of the buildings and allocates those calls to the various cars for response, and distrib­utes cars among the floors of the building, in accordance with any one of several various modes of group operation. Modes of group operation may be controlled in part, for example, by a lobby panel ("LOB PNL") 21, which is normally connected by suitable building wiring 22 to the group controller in multi-car elevator systems.

[0060] The car controllers 15, 16 also control certain hoistway functions, which relate to the corresponding car, such as the lighting of "up" and "down" response lanterns 23, 24, there being one such set of lanterns 23 assigned to each car 3, and similar sets of lanterns 24 for each other car 4, designating the hoistway door where service in response to a hall call will be provided for the respective up and down directions.

[0061] In the prior art the position of the car within the hoistway is derived from a primary position transducer ("PPT") 25, 26. Such a transducer is driven by a suitable sprocket 27, 28 in response to a steel tape 29, 30, which is connected at both of its ends to the cab and passes over an idler sprocket 31, 32 in the hoistway well.

[0062] Similarly, although not required in an elevator system to practice the present invention, a secondary position transducer ("SPT") 33, 34 may be employed for obtaining additional detailed positional information at each floor for more door control and for verification of floor position information derived by the "PPT" 25, 26. Or, if desired, the elevator system in which the present invention is practiced may employ inner door zone and outer door zone hoistway switches of the type known in the art.

[0063] The foregoing is a description of an elevator system in general, and, as far as the description goes thus far, is equally descriptive of elevator systems known to the prior art, as well as an exemplary elevator system which could incorporate the teachings of the present invention.

[0064] All of the functions of the cab itself may be directed, or communicated with, by means of a cab control­ler 35, 36 in accordance with the present invention, and may provide serial, time-multiplexed communications with the car controller, as well as direct, hard-wired communi­cations with the car controller by means of the traveling cables 13 & 14. The cab controller, for instance, can monitor the car call buttons, door open and door close buttons, and other buttons and switches within the car. It can also control the lighting of buttons to indicate car calls and provide control over the floor indicator inside the car, which designates the approaching floor.

[0065] The cab controller 35, 36 may interface with load weighing transducers to provide weight information used in controlling the motion, operation, and door functions of the car.

[0066] An additional function of the cab controller 35, 36 is to control the opening and closing of the door, in accordance with demands therefor, under conditions which are determined to be safe.

[0067] The makeup of microcomputer systems, such as may be used in the implementation of the car controllers 15, 16, a group controller 17, and the cab controllers 35, 36, can be selected from readily available components or families thereof, in accordance with known technology, as described, for example, in various commercial and technical publica­tions. The software structures for implementing the present invention, and peripheral features which may be disclosed herein, may be organized in a wide variety of fashions.

[0068] The "smart" primary position transducer's central processor unit (SPPT-CPU) used in the present invention is a subsystem of the overall modular control system for the elevator system. It is designed to perform a number of tasks related to the position and velocity of the elevator with which it is associated and the status of the SPPT system as well.

[0069] The major function of the SPPT-CPU is to transform the accumulated pulse train signals received from the encoders into position and velocity information. This information, along with speed check and battery status, are communicated to the motion control subsystem (MCSS-CPU) for the elevator upon request.

[0070] As can be seen in Figure 3, the SPPT (which includes the encoder assembly or PPT) interfaces with the motion command subsystem (MCSS) and the power supply subsystem (PSSS) of the MCSS. In essence the SPPT is made up of the SPPT's CPU and the encoder assembly or PPT.

[0071] The SPPT-CPU hardware is comprised of two identical circuits for the counting and storage of transducer inputs, configured into, for example, six basic elements. These exemplary basic elements include one circuit board assembly (CBA), one position transducer (PT), one position transduc­ er housing, one battery backup, and two cable assemblies - one (W1, W2) for the encoder signal and the other (W3) for the power signal.

[0072] The exemplary CBA for the SPPT-CPU includes three connectors, two ten pin connectors (W1, W2) to the trans­ducer encoder and a twenty-six pin connector (W3) to the MCSS-CPU and its power supply and lackup battery. Through the latter connector (W3) the CBA interfaces with the primary position transducer (J2), the secondary position transducer (J1), the power supply and the battery backup (J3).

[0073] The J2 connector (PPT) receives the pulse train used to determine the position and direction of the travel of the elevator car. The secondary PT is mainly a backup system (through J1) to provide slowdown, if the PPT signals are lost when approaching either terminal landing.

[0074] All position and velocity signals can be in the form of "RS-422" serial communication.

[0075] Figure 5 shows the functional blocks of the SPPT CBA, showing the interfacing of its various elements through the Address, Data buses and I/O ports. The exemplary SPPT-CPU board includes:
■ a 80C31 micro-controller;
■ 128-byte of internal RAM;
■ synchronized encoder circuitry;
■ a 20 bit pre-load up/down counter;
■ 24 bit latched pre-load count and status;
■ latched address/data multiplexed;
■ coarse count and edge detect circuitry;
■ watchdog circuitry;
■ 8K X 8 program memory (EPROM); and
■ devices select and serial communication interfaces; all as more particularly detailed in Figure 5. The secondary processor is similar, with the signals "J", "K", "A90" and "B" being substituted for the signals "X", "Y", "A" and "B90" of Figure 5, respectively.

- Encoders -

[0076] The PPT of the exemplary embodiment can use the same mechanical connections and electrical signals of its predecessor units.

[0077] The PPT includes preferably two encoders coupled by, for example, "256:257" gearing. The encoders prefera­bly are of identical design, and in the preferred embodi­ment contain two - one thousand and twenty four (1024) pulses per revolution (ppr) - fine tracks, and two - one ppr - coarse tracks.

[0078] Each pair of tracks produce signals that are in quadrature with each other. Further, the registration between the coarse and fine tracks is controlled.

[0079] The directly-driven encoder is termed the "primary encoder" and is connected directly to an appropriately toothed gear, for example, a two hundred and fifty-six (256) tooth gear. The other encoder is termed the "second­ary encoder" and is connected to the primary encoder by means of a different toothed gear, for example, a two hundred and fifty-seven (257) tooth gear. The difference in the number of teeth in the gears used for the otherwise identical two transducers produces a non-"1:1" ratio, namely in the preceding example, a "257/256" ratio of secondary to primary.

[0080] Exemplary signal definitions for the two encoders are outlined below
Primary Encoder:
"X" - 1024 ppr fine track;
"Y" - 1024 ppr fine quadrature track
"A" - 1.0 ppr coarse track
"A90" - 1.0 ppr coarse quadrature track.
In the case of the secondary encoder, signals "J", "K", "B" & "B90" correspond, respectively, to "X", "Y", "A" & "A90" for the primary encoder.

[0081] Each set of signals is derived from an encoder whose design preferably is identical to the other encoder. The periods of the signals coming from the secondary encoder are, in the exemplary embodiment, "257/256" times those for the primary encoder.

[0082] The main and quadrature fine track signals are processed by external circuitry, well known to those of ordinary skill in the art. This processing results in a "x4" (four times) frequency multiplication, and a determi­nation of the direction of rotation. For each upward and downward transition on the main and quadrature tracks, an upward going transition occurs in the output of the "x4" multiplication circuitry. The performance of the position transducer is evaluated by examining the fine track signals, as processed by the multiplication circuitry.

[0083] Between the upward and downward transitions for each coarse track, there are, for example, two thousand and forty eight (2,048±1), plus or minus one transition, in the associated "x4" fine track.

[0084] For clockwise rotation of the input shaft, the offset between upward transitions of signals "A" and "A90" will be one thousand and twenty four (1,024±1), plus or minus one, "x4" "XY"-track counts. Similarly, the offset between upward transitions of signals "B" and "B90" will be one thousand and twenty four (1,024±1), plus or minus one, "x4" "JK"-track counts.

[0085] Performance is characterized by a measurement of "x4" (four times) "XY"-track counts between upward transi­tions of the "A" & "B90" tracks, as the input shaft is rotated clockwise (from the perspective of viewing the instrument's input shaft). For each revolution of the input shaft a new count is developed and two hundred and fifty six (256) distinct counts may be obtained. The pattern of two hundred and fifty six (256) distinct counts may be obtained. The pattern of "256" counts repeats as the input shaft is turned.

[0086] For a counter-clockwise rotation of the input shaft, the "x4" "XY"-tracks counts preferably is measured between downward transitions of the "B90" and "A"" tracks. This procedure assures the use of the same mechanical reference points in the instrument.

[0087] The count can go to, for example, four thousand and ninety six (4,096), which is "1000" in hexadecimal form ("HEX"). The last HEX digit is called the "remainder". The scatter of the remainder numbers determines the quality of the position transducer.

[0088] It is desirable that the remainder, as defined above, shall remain within a boundary of plus or minus two (±2). This means that all "256" test numbers must have stable remainders for all specified speeds, in both directions of rotation, independent of temperature, etc.

[0089] The remainder, as defined above, is measured for all rotations of the input shaft using the "A90" and "B" tracks instead of the "A" and "B90" tracks. The remainder thus measured is the quadrature remainder. It should meet the same requirements as the other remainder.

[0090] To connect the encoders of the "smart" transducer to the SPPT CBA two cables of, for example, the ribbon form, are used. These cables are terminated in appropriate connectors.

[0091] The main channel leads the quadrature channel for clockwise rotation of the shaft, as viewed from the shaft end of the units. This applies to (X, Y), (J, K), (A, A90) and (B, B90) and their complements.

[0092] With the input shaft rotating clockwise, the primary encoder turns clockwise, while the secondary encoder turns counter-clockwise. Thus, "X" leads "Y", "K" leads "J", "A" leads "A90" and "B90" leads "B".

- DETERMINATION OF POSITION & VELOCITY INFO. -

[0093] As noted above, in the exemplary embodiment the encoders have two sets of direct and quadrature tracks. The fine tracks produce "1024" pulses per revolution, and the coarse tracks are one ppr. When combined with times four (x4) circuitry, the effective resolution of the fine tracks is four thousand and ninety six (4,096) pulses (12 bits) per revolution. The coarse track geometry is very carefully controlled.

[0094] The primary encoder is directly driven, while the secondary encoder is driven through a gear system (note e.g. Figure 7 embodiment). Position increments are derived from the primary fine tracks. Absolute position at "256" points (8 bit) can be established from the (spatial) phase of one coarse track on the primary encoder with respect to a coarse track on the secondary encoder. To determine coarse track phasing may require as many as two revolutions of the input shaft. The total range of the transducer is defined by "256" revolutions of the input shaft.

[0095] The absolute position readouts are characterized by (spatially derived) signals that can go to "4096" or "1000" in hexadecimal. The first part of the HEX number is coarse position (zones "0" to "255" decimal). The last digit is the remainder number. The transducer is designed so that the remainder is close to "8" HEX to permit ignoring it using a truncation (shift right) operation.

[0096] The determination of position for the primary channel requires the finding of coarse position and then adding incrementally derived fine positions to it. Further, for reasons of elevator safety, a redundant secondary position is required. This is accomplished using hardware that is independent of that used for the primary position.

[0097] Described below are the procedures which can be used to find the primary and secondary position and velocity. The basic signal processing operations and power supply subsystem are shown in the block diagram of Figure 6. Exemplary details of the speed check circuitry of Figure 6 are shown in Figure 4. As can be seen in Figure 4, comparators for the primary velocity signal (PRI. VEL.) and the secondary velocity signal (SEC. VEL.) using a "REFER­ENCE SIGNAL" are sent to an "AND" gate, which when the signals are appropriately related sends out "SAFE" signals through an "RS-422 DRIVER".

[0098] Another exemplary SPPT using absolute encoders is depicted in the electro-mechanical block diagram of Figure 7, in which the "INPUT SHAFT" drives a twelve (12) bit absolutely encoded disk. This same "INPUT SHAFT" drives gearing that turns one or more turns-counting coarse encoders through gearing, an exemplary two such coarse encoders, "COARSE #1" and "COURSE #2" disks being illus­trated. Each disk [whether primary, coarse "#1", coarse "#2", etc.] has two independent read-heads, namely, "FP" & "FS" for the primary "FINE DISK", and C1P" & "C1S" for "COARSE #1 DISK", and "C2P" & "C2S" for "COARSE #2 DISK," respectively, for the primary & secondary signals, respec­tively. The signals from the primary read-heads are input to the primary processor, while those from the secondary read-heads are input to the secondary processor. The primary and secondary processors are independent. These processors are connected to speed-check circuitry, which can be of the comparator type shown in Figure 4. The encoders and electronic assemblies are typically housed in a common case.

[0099] For the embodiment of Figure 6, the fine counts are derived from the fine tracks on each encoder. Times four "x4" multiplication is provided so that every edge of each direct and quadrature track pair is utilized. The track processing hardware and software provides either a separa­tion of pulses resulting from opposite directions of rotation, or assignment of a sign to each pulse based on direction of rotation.

[0100] The fine track of the primary encoder is "X" and the quadrature track is "Y". The "x4" composite signal is called "XY". "4096" ("1000" HEX) XY pulses are produced per revolution of the input shaft. "256" revolutions of the input shaft produces "100000" HEX (1,048,576) counts.

[0101] The fine track of the secondary encoder is "J" and the quadrature track is "K". The "x4" composite signal is called "JK". JK counts may be referenced to XY counts by multiplying the JK counts by "257/256 =1 + 1/256". In HEX arithmetic this may be accomplished by adding the JK count to the JK count with the two least significant digits truncated. JK counts referenced to the primary encoder should meet the same specifications as the XY counts.

[0102] The primary and secondary coarse positions are defined by measuring the number of fine counts between transitions defined by the coarse tracks. Definitions are given for a transducer having clockwise (viewing the instrument shaft) as a positive direction. The transducer should also be capable of operating with counter-clockwise defined as the positive direction. The technique for realizing a reverse-direction transducer is provided below.

[0103] The primary encoder coarse track is called "A" and the associated quadrature track is called "A90". The corresponding terminology applied to the secondary encoder is "B" and "B90".

[0104] For clockwise rotation of the input shaft, coarse primary position is found by first determining the number of "XY" counts between an upward transition of A to the immediately following upward transition of B90. The last four (4) bits are then truncated from the XY count to obtain the coarse position. These truncated bits define the remainder number.

[0105] For counter-clockwise rotation of the input shaft, XY counts are determined from a downward transition of B90 to the next downward transition of A. The coarse position and reminder number are defined as before.

[0106] The measurement procedure assures the use of the same mechanical reference points in the transducer instru­ment.

[0107] For clockwise rotation of the input shaft, coarse secondary position is found by first determining the number of JK counts between an upward transition of A90 to the immediately following upward transition of B. The JK count is next referenced to the primary fine count by multiplying by "257/256". The truncated portion is then truncated from the derived XY count to obtain the coarse position. The truncated portion is called the quadrature remainder number.

[0108] For counter-clockwise rotation of the input shaft, JK counts are determined from a downward transition of B to the next downward transition of A90. The coarse position and quadrature remainder number are defined as before.

[0109] As above, the measurement procedure assures the use of the same mechanical reference points in the instrument.

** Primary Position **

[0110] Primary position as a HEX number consists of:
PRI_POS = COARSE_PRI_POS * 1000 + FINE_PRI_POS
where FINE_PRI_POS is derived from the XY counts and equals "000" at the end of each coarse primary position determina­tion cycle.

[0111] Two basic techniques exist for determination of primary position once the transducer system is initialized.

[0112] The first technique is to update the coarse position based upon the fine position. When FINE_PRI_POS = 1000, the coarse position is incremented by one count and FINE_PRI_POS is reset to be equal to "000". More, general­ly, FINE_PRI_POS is divided by "1000" and the result is added to COARSE_PRI_POS, and FINE_PRI_POS is reset to the remainder (local remainder, not the previously defined remainder number).

[0113] If FINE_PRI_POS goes negative, COARSE_PRI_POS should be decremented and FINE_PRI_POS reset accordingly. On an interim basis, the fine position must always be character­ized by a magnitude and sign. When the reckoning for position is complete, then fine position is always a positive number.

[0114] The second technique or method is to update the coarse position directly by measurement. To do this FINE_PRI_POS is set equal to the appropriate value immedi­ately after the completion of the update.

[0115] The first technique or method should always be used, while the second technique or method should be used whenever no direction reversals are used during the measurement process.

[0116] A disagreement of up to, for example, ten (10) counts may be permitted without the need to re-initialize. If the disagreement is up to, for example, five (5) counts, no correction referenced to the second method is required. A disagreement in the range of, for example, five to ten (5-10) counts for, for example, two consecutive position determinations by the second method requires adjusting the method one position to agree with method two.

** Primary Velocity **

[0117] The absolute primary velocity (HEX) is computed from the PRIMARY POSITION. Thus:
ABS_PRI_VEL(N)=
[ PRI_POS(N-1)-PRI_POS(N-2) /1000] * (60/T)_HEX
where N is the present cycle, N-1 is the previous cycle, etc., T = cycle time, which is measured in decimal seconds.

[0118] For T=10ms, (60/T) is HEX number "1770". The above expression should be scaled to a "0.25" rpm/count by multiplying by four (4). To get the PRI_VEL from the absolute value when the velocity is negative, "800" HEX should be added to the ABS_PRI_VEL.

[0119] For example, at "511.75" rpm the PRI_VEL=7FF HEX. It is FFF HEX at "-511.75" rpm.

[0120] The PRI_VEL should be subjected to a running average over a period of, for example, seventy to ninety (70-90ms) milliseconds prior to transmission.

[0121] The above computation should be first or very close to first in a cycle to assure accuracy. It should be noted that the velocity is determined using position data from two previous cycles.

** Secondary Position **

[0122] The secondary position as a HEX number consists of:
SEC_POS =
(COARSE_SEC_POS*1000 + SEC_FINE_POS) * (101/100)_HEX
where SEC_FINE_POS is derived from JK counts, and SEC_FINE_POS=000 at the end of each coarse secondary position determination cycle.

[0123] Two basic techniques or methods exist for the deter­mination of secondary position once the transducer system has been initialized.

[0124] The first method is to update the coarse position based upon the fine position. When SEC_FINE_POS=FF0, the coarse position is incremented by one count and SEC_FINE_POS is reset to "000". More generally, SEC_FINE_POS is divided by "FF0" and the result is added to COARSE_SEC_POS, and SEC_FINE_POS is reset to the remainder (local remainder, not the previously defined remainder number).

[0125] If SEC_FINE_POS goes negative, COARSE_SEC_POS should be decremented, and SEC_FINE_POS reset accordingly. On an interim basis, fine position should always be characterized by a magnitude and sign. When the reckoning for position is complete, then the fine position is always a positive number.

[0126] The second method is to update the coarse position directly by measurement. SEC_FINE_POS is set to be equal to an appropriate value immediately after completion of the update.

[0127] The first method should always be used. The second method should be used whenever there are no direction reversals during the measurement process.

[0128] A disagreement of up to, for example, ten (10) counts may be permitted without the need to re-initialize. If the disagreement is up to, for example, five (5) counts, no correction referenced to the second method is required. A disagreement in the range of, for example, five to ten (5-10) counts for, for example, two consecutive position determinations by the second method requires adjusting the method one position to agree with method two.

** Secondary Velocity **

[0129] The absolute secondary velocity (HEX) is computed from the SECONDARY POSITION. Thus:
ABS_SEC_VEL(N)=
[ SEC_POS(N-1)-SEC_POS(N-2) /1000] * (60/T)_HEX
where T = cycle time, which is measured in decimal seconds.

[0130] For T=10ms, (60/T) is HEX number "1770". The above expression should be scaled to a "0.25" rpm/count by multiplying by four (4). To get the SEC_VEL from absolute value when the velocity is negative, "800" HEX should be added to the ABS_SEC_VEL.

[0131] For example, at "511.75" rpm the SEC_VEL=7FF HEX. It is FFF_HEX at "-511.75" rpm.

[0132] The SEC_VEL should be subjected to a running average over a period of, for example, seventy to ninety (70-90ms) milliseconds prior to transmission.

** Initialization **

[0133] Initialization is the determination of the coarse position after the first power up or after a request to reset the processor system. Primary and secondary position and battery condition are transmitted according to the protocol desired. If the coarse position is unknown, then the transducer signals this by transmitting the position as "00000H". The elevator should respond by slowly moving down unless it is determined to be too close (less than, for example, four meters) to the lowest landing.

[0134] It is highly desirable that the system includes a speed check. Such a speed check should become active within, for example, one hundred (100ms) milliseconds of power application. Unless the speed check signal is high (safe), initialization should not be allowed to start.

[0135] The transducer should determine the primary and secondary positions according to the indicated second methods above. Once accomplished, the transducer will be prepared within, for example, one processor cycle to transmit both the primary and secondary positions to the elevator system. The elevator system will continue to run a short distance even if both positions are not estab­lished. It will expect that both position signals will be established within, for example, a half meter (0.5m;¼ revolution, nominal) of each other. The half meter distance should be established by the elevator system using both the acquired position signal and the permitted running time.

[0136] Failure to initialize will cause the elevator system to stop and also send a reset signal to the transducer. Initialization will then be attempted one or more times before the elevator enters the "rescue" mode and finally is closed down for service.

[0137] An exemplary battery backup system should retain all stored information for, for example, an hour after any loss of main power. Within that time period, re-initial­ization typically should not be necessary.

** Polarity Reversal **

[0138] Polarity reversal is necessary as a practical matter to meet different transducer mounting situations. This may be accomplished by the following algorithms expressed in HEX (2's complement):
PRI_POS = 100000 - PRI_POS
SEC_POS = 100000 - SEC_POS
The primary velocity and the secondary velocity given above in the calculation subsection must be reversed when a polarity reversal is indicated. This can be done by changing the sign bit.

** Independence, Adjustments & Safeguards **

[0139] In the "real world" adjustments to the date are required because of, for example, imperfections in encoders and the basic characteristics of the transducer system.

[0140] For example, two (2) counts should be added to the un-truncated, primary, coarse position, so that on average the remainder number preferably is, for example, "8". A similar procedure should be followed for the secondary coarse position. Two (2) counts should be subtracted from the un-truncated, coarse, secondary position.

[0141] Additionally, the secondary position should be made to register with the primary position within, for example, five (5) counts.

[0142] In data transmission the secondary position signal may be truncated to the most significant sixteen (16) bits of data prior to transmission.

[0143] Vibratory motion of the transducer input shaft about a reference point could lead to errors, especially in the determination of coarse position. Thus, all coarse position measurements based on the second method above should be carried out in their entirety only when the motion of the elevator car is in one direction. The first methods above may be used for all speeds.

[0144] In order to assure independence and the integrity of the primary position information, the signals A and B90 should be monitored every process or cycle. The integrity of these signals should be established by checking the "on" and "off" periods in terms of the XY counts. The period for A should be, for example, "2048±35" counts, while the period for B90 should be "2056±35" counts.

[0145] Likewise, in order to assure the independence and integrity of the secondary position information, the signals A90 and B should be monitored every process or cycle. The integrity of these signals should be estab­lished by checking the "on" and "off" periods in terms of the JK counts. The period for A90 should be, for example, "2040±35" counts, while the period for B should be "2048±35" counts.

[0146] Upon detection of any fault in a processing channel, the "not initialized" signal should be transmitted on that channel. Simultaneously, recovery action should commence.

[0147] Although this invention has been shown and described with respect to a detailed, exemplary embodiment thereof, it should be understood by those skilled in the art that various changes in form, detail, methodology and/or approach may be made without departing from the scope of this invention.

Claims

1. An elevator system, in which there is at least one elevator car whose speed is controlled by a motion control subsystem and in which there is to be included a transducer system for determining the vertical position of the car in the elevator run by providing a binary representation of the number of revolutions made by a rotatable shaft to which a transducer is connected, which shaft carries a movable encoder element having at least two coded tracks, a fine track and a relatively coarse track, made up of sensible indicia, said transducer system includ­ing:
sensing means related to each track for sensing the indicia thereon to provide signals indicative of the movement of the encoder element from a reference position; and
signal processing means associated with said sensing means responsive to the signals corresponding to the fine coded track and to the relatively coarse coded track for providing a binary signal representation of the relative position of the encoder element and responsive to the signals corresponding to both of the coded tracks to provide, as a function of the number of coded track indicia which have been sensed indicated thereby, a binary signal representation of the total movement the encoder element has moved from the reference position; characterised in that said transducer system further comprises:
independent means for finding at least two independent position and velocity signals, or derivatives of these signals, with an instrument having a single, common input shaft.

2. The elevator transducer system of Claim 1, wherein said independent means comprises:
an incremental system in which said encoder element includes a single, rotatable encoder disk with at least one encoded track and at least two read-heads associated with said track producing said signals.

3. The elevator transducer system of Claim 1, wherein said independent means comprises:
a quasi-absolute system using differential gearing producing two independent position and speed signals.

4. The elevator transducer system of Claim 1, wherein said independent means comprises an absolute system including:
a main disk attached to the input shaft;
additional absolute encoders coupled to the input shaft through gearing determining the turns of the main shaft; and
at least two independent position and velocity output signals being obtained by use of independent sets of read-heads located circumferentially about each disk, a primary, output signal being used to run the elevator and the other, secondary, output signal being used for normal terminal protection.

5. The elevator transducer system of Claim 4, wherein there is included speed check means for deriving a door zone speed check signal from a combination of said primary and secondary velocity output signals, providing an independent means for checking elevator car speed in the door zone.

6. An elevator system, in which there is at least one elevator car whose speed is controlled by a motion control subsystem and in which there is to be included a transducer system for determining the vertical position of the car in the elevator run by providing a binary representation of the number of revolutions made by a rotatable shaft to which a transducer is connected, which shaft carries a movable encoder element having coded tracks, including at least a fine track and a relatively coarse track, made up of sensible indicia, said transducer system including:
sensing means related to each track for sensing the indicia thereon to provide signals indicative of the movement of the encoder element from a reference position; and
signal processing means interconnected to said sensing means responsive to the signals corresponding to the fine coded track and to the relatively coarse coded track for providing a binary signal representation of the relative position of the encoder element and responsive to the signals corresponding to both of the coded tracks to provide, as a function of the number of coded track indicia which have been sensed indicated thereby, a binary signal representation of the total movement that the encoder element has moved from the reference position; characterised in that said transducer system further comprises:
a primary encoder directly driven by the shaft providing primary position signals and primary velocity signals indicative of the location and velocity of the elevator car;
a secondary encoder coupled to said primary encoder by gearing, which causes said encoders to rotate at different rotational speeds, providing secondary position and velocity signals indicative of the location and velocity of the elevator car; each of said encoders including at least one fine track and at least one rela­tively coarse track each made of sensible indicia, said fine track having many more sensible indicia in its track in comparison to said coarse track; and
position and velocity determination means associated with said encoders for generating signals indicative of the position and the velocity of the elevator car using two independent channels, providing with said sensing means effective means for generating at least two, independent, position and speed signals using a single input shaft.

7. The elevator transducer system of Claim 6, wherein:
said primary and said secondary encoders each include an encoded track utilizing multiple read-heads in association with each encoded track.

8. The elevator transducer system of claim 6 or 7 wherein:
said position and velocity determination means generates signals based on the relationship of finding the coarse position and then adding incrementally derived fine positions to it.

9. The elevator transducer system of claim 6 or 7 wherein:
said position and velocity determination means generates signals based on two methods, a first method of updating the coarse position based on the fine position, and a second method based on updating the coarse position directly by measurement.

10. The elevator transducer system of claim 9, wherein:
said position and velocity determination means, when in operation, always generates signals based on said first method and generates signals based on said second method whenever the direction of the car does not reverse during the cycle of the measurement involved.

11. The elevator transducer system of claim 10, wherein:
said position and velocity determination means follows "disagreement" algorithm based on the comparison of the position signals generated in said first method to the signals generated in said second method to maintain the integrity of the data represented by said signals.

12. The elevator transducer system of any of claims 6 to 11, wherein:
said gearing includes mating gear wheels having 256 teeth on the gear wheel of said primary encoder and 257 teeth on the gear wheel of said secondary transducer.

13. The elevator transducer system of any of claims 6 to 12, wherein said position and velocity determination means generates signals indicative of primary position (PRI_POS) based on the relationship expressed as a HEX number of:
PRI_POS = COARSE_PRI_POS * 1000 + FlNE_PRI_POS
where FINE_PRI_POS is derived from the XY counts and equals "000" at the end of each coarse primary position determina­tion cycle; where the fine track of the primary encoder is "X", the quadrature track is "Y", and the times four ("x4") composite signal is "XY".

14. The elevator transducer system of any of claims 6-13, wherein said position and velocity determination means generates signals indicative of the absolute primary velocity (ABS_PRI_VEL) based on the relationship expressed as a HEX number of:
ABS_PRI_VEL(N)=
[ PRI_POS(N-1)-PRI_POS(N-2) /1000] * (60/T)_HEX
where T = cycle time.

15. The elevator transducer system of any of claims 6-14, wherein said position and velocity determination means generates signals indicative of secondary position (SEC_POS) based on the relationship expressed as a HEX number of:
SEC_POS =
(COARSE_SEC_POS*1000 + SEC_FINE_POS) * (101/100)_HEX
where SEC_FINE_POS is derived from JK counts, and SEC_FINE_POS=000 at the end of each coarse secondary position determination cycle; where the fine track of the secondary encoder is "J", the quadrature track is "K" and the times four ("x4") composite signal is "JK".

16. The elevator transducer system of any of claims 6-15, wherein said position and velocity determination means generates signals indicative of absolute secondary velocity (ABS_SEC_VEL) based on the relationship expressed as a HEX number of:
ABS_SEC_VEL(N)=
[ SEC_POS(N-1)-SEC_POS(N-2) /1000] * (60/T)_HEX
where T = cycle time.

17. The elevator transducer system of any of claims 6-16, wherein the transducer includes polarity reversal means for reversing the signal polarity by the following algo­rithm expressed in HEX (2's complement):
PRI_POS = 100000 - PRI_POS
SEC_POS = 100000 - SEC_POS
with the primary velocity and the secondary velocity being reversed when a polarity reversal is indicated by changing the sign bit of the signal.

18. A method of providing position information on a car in an elevator system, in which there is at least one elevator car whose speed is controlled by a motion control subsystem and in which there is included a transducer system determining the vertical position of the car in the elevator run by providing a binary representation of the number of revolutions made by a rotatable shaft to which a transducer is connected, which shaft carries an encoder element having at least two coded tracks, a fine track and a relatively coarse track, made up of sensible indicia, said transducer system including:
sensing means related to each track for sensing the indicia thereon to provide signals indicative of the movement of the encoder element from a reference position; and
signal processing means interconnected to said sensing means responsive to the signals correspond­ing to the fine coded track and to the relatively coarse coded track for providing a binary signal representation of the position of the encoder element and responsive to the signals corresponding to both of the coded tracks to provide, as a function of the number of coded track indicia which have been sensed indicated thereby, a binary signal representation of the total movement that the encoder element has undergone from its reference position;
comprising the following steps:

(a) using a primary encoder directly driven by the shaft for providing primary position signals and primary velocity signals indicative of the location and velocity of the elevator car;

(b) using a secondary encoder coupled to said primary encoder by gearing, which causes said encoders to move at different speeds, for providing secondary position and velocity signals indicative of the location and velocity of the elevator car; each of said encoders including at least one fine track and at least one relatively coarse track each made of sensible indicia, said fine track having many more sensible indicia in its track in comparison to said coarse track; and

(c) using position and velocity determination means associated with said encoders for generating signals indicative of the position and the velocity of the elevator car using two independent channels, producing with said sensing means effective means for generating at least two, independent, position and speed signals using a single input shaft.

Drawing