Apparatus and methods for incrementally stepping a printer drive shaft

Abstract

 A paper feed drive shaft in a printer is directly coupled at each of its opposite ends to stepper motors. The stepper motors directly drive the paper feed shaft and are actuated either synchronously or asynchronously. By directly coupling the motors and shaft, torsional vibration in the shaft and consequent high acoustical noise levels as well as paper settling times may be minimized by the phasing of the applied step timing signals to the motors.

Description

BACKGROUND AND SUMMARY OF THE INVENTION

[0001] The present invention relates to apparatus and methods for incrementally stepping the rotary drive shaft for the paper feed in a printer and particularly relates to apparatus and methods for minimizing or eliminating the torsional vibration in rotary paper feed drive shafts for high-speed printers and consequent acoustic noise levels and paper settling times.

[0002] Conventional impact printers advance the paper by using tractor assemblies driven by a single motor which are usually coupled together by a toothed belt and gearing arrangement. This toothed belt arrangement enables conversion of the angular displacement of the motor for a given paper movement. An arrangement such as this is described in co-pending application Serial No. 07/400,001, filed August 29, 1989 for "Printer and Cartridge Assembly Therefor."

[0003] Another conventional printer employs two motors to drive the paper. One motor is used to drive the paper for short, quick moves. The other motor is used to drive the paper for long, high-speed, non-printing, moves. The motors, however, are not used simultaneously and are not directly coupled to the paper feed drive shaft.

[0004] Another known printer uses a stepper motor coupled directly to the tractor assembly drive shaft. The stepper motor is appropriately sized to provide a minimum step for the corresponding minimum paper advance so that no belt or gear reduction is needed. The motor bearings support the end of the tractor shaft on which the motor is mounted, while the opposite end is mounted in suitable bearings.

[0005] It has been found that when a stepper motor is directly coupled to the drive shaft of the printer, and the motor is stepped at high acceleration rates, the drive or tractor shaft, conventionally longer than the width of the paper being fed through the printer, e.g., on the order of 20 inches, torsionally vibrates. This is a result of high frequencies associated with the leading edges of the acceleration and deceleration fronts generated by the stepper motor and its direct coupling at one end of the shaft. The higher the acceleration, the greater the torsional vibration and acoustic noise levels. For example, for high speed printers, it is desirable to index the drive shaft 1° of rotary movement in about 2 milliseconds. One degree of rotary movement is tantamount to advancing the paper one dot row of print in a dot matrix printer. A print line conventionally contains 7-9 dot rows. The minimal time of about 2 milliseconds for a paper advance corresponding to 1° of rotation of the paper feed drive shaft is approximately equal to the turnaround time of the shuttle for the printer. Consequently, these high operating speeds produce a torsional vibration along the length of the drive shaft, causing an unduly high acoustic noise level and lengthened paper settling time due to backlash and loss of motion in the paper feed mechanism.

[0006] According to the present invention, the torsional vibrational effects resulting in high acoustical noise and protracted paper settling time are minimized or eliminated. To accomplish this, stepper motors are directly coupled to each of the opposite ends of the paper feed drive shaft. The two motors may be individually smaller than the single motor located at one end of the shaft in the previously described conventional printer. Each motor is directly and rigidly coupled to the shaft through any suitable coupling, for example, a collet clamp arrangement may be used. One advantage of the present invention resides in the fact that no additional bearings are necessary at the opposite ends of the shaft because the paper feed drive shaft is mounted essentially in the motor bearings. Each motor is also electronically damped and this electronic damping is applied simultaneously to both ends of the shaft for effective quieting. This electronic damping is in the form of timing the application of forward and/or reverse steps to the motors as they are stepped along, and notably when they are just coming to rest at the completion of a quick paper movement.

[0007] In a preferred embodiment of the present invention, each motor is powered through its own separate amplifier and inputs to the amplifiers are then paralleled. Alternatively, both motors can be operated in series or parallel from a common power amplifier.

[0008] The motors in the present invention may be operated synchronously or slightly out of phase one with the other. To accomplish synchronous operation with the motors sourced by their respective power amplifiers, a separate predetermined timing input signal may be applied to each of the power amplifiers therefor. If the motors are operated in parallel or in series, a single timing input may be provided to the common power amplifier. The motors may be operated out of phase by employing a delay in the trailing input signal. By operating out of phase, the torsional front, i.e., the acceleration or deceleration of one motor may be desirably cancelled out at about the center of the drive shaft whereby torsional and acoustical noise levels are diminished or eliminated.

[0009] In a preferred embodiment according to the present invention, there is provided a printer comprising a paper feed drive shaft for the printer, paper-engaging elements connected to and driven by the drive shaft and a pair of stepper motors connected directly to the opposite ends of the drive shaft for directly stepping the drive shaft.

[0010] In a further preferred embodiment according to the present invention, there is provided a method for advancing paper in a printer comprising the steps of coupling the opposite ends of a printer feed drive shaft directly to a pair of stepper motors, respectively and energizing both motors to rotate the drive shaft through a single predetermined rotary increment.

[0011] In a further preferred embodiment according to the present invention, there is provided, in a servo-mechanism including a long, slender shaft having a ratio of length to diameter of at least 20 to 1, a method of incrementing rotation of the shaft comprising the steps of coupling each end of the shaft to a respective drive motor, and energizing both motors to rotate the shaft through predetermined rotary increments so as to control the delay in response of one end of the shaft with respect to the other end.

[0012] Accordingly, it is a primary object of the present invention to provide novel and improved apparatus and methods for incrementally stepping the paper feed drive shaft in a high-speed printer to minimize or eliminate torsional vibration in the shaft and consequent high acoustical noise levels and paper settling time. This objective is accomplished principally by providing a direct connection between a stepper motor and the paper feed drive shaft at each of the opposite ends of the drive shaft, the motors being driven either synchronously or non-synchronously, with resulting reduction in acoustical noise and paper settling time.

[0013] These and further objects and advantages of the present invention will become more apparent upon reference to the following specification, appended claims and drawings.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0014] 

Figure 1 is a perspective view of a printer incorporating a paper drive shaft and stepper motor arrangement constructed in accordance with the present invention;

Figure 2 is an enlarged top plan view of a tractor assembly with parts broken out for clarity illustrating the application of the stepper motors directly to the paper feed drive shaft of the printer; and

Figures 3 and 4 are schematic views of two embodiments of respective electrical circuits for the stepper motors and shaft.

DETAILED DESCRIPTION OF THE DRAWINGS FIGURES

[0015] Reference will now be made in detail to the present preferred embodiment of the invention, an example of which is illustrated in the accompanying drawings.

[0016] Referring now to Figure 1, there is illustrated a printer, generally designated P, for printing on paper, designated 10, exiting the printer through a printer exit slot 12. The printer P may be of the shuttle type, in which a shuttle oscillates along the width of the paper and carries actuators for applying dots along a print line. Dot matrix shuttle-type printers of this type are well known in the art and further description thereof is believed unnecessary. Suffice to say that the paper 10 will be advanced incrementally one dot row at a time, 7-9 dot rows being necessary to form a line of print.

[0017] While a printer employing the paper drive mechanism of the present invention may use a single paper shaft with rollers to incrementally advance the paper, such arrangement lying within the scope of the present invention, a particular embodiment of the present invention employs a tractor assembly, generally designated 14, for advancing the paper, and illustrated in Figure 2. Tractor assembly 14 is conventional, except for the drive therefor, and includes a pair of end plates 16, coupled one to the other by a pair of support rods 18 and 20 mounting paper guides 22. Tractors 24 are also carried by support rod 18 and are driven by the drive shaft 26. Tractors 24 are conventional and include a plurality of pins 28 which engage through the paper feed holes along the margins of the paper. The pins are mounted on endless loops, not shown, which are driven by shaft 26. The paper is clamped between each tractor assembly and its pivoted covers 30. It will be appreciated that rotation of drive shaft 26 advances the pins 28 whereby the paper is incrementally advanced through the printer. Drive shaft 26, of course, may extend beyond the ends of end plates 16.

[0018] In accordance with the present invention, drive shaft 26 at each of its opposite ends is directly coupled to a stepper motor 32. This direct coupling is provided by a direct rigid clamping of the motor drive shaft and paper feed drive shaft 26. This can be accomplished in a variety of ways. Any standard type of clamp which directly transmits the rotary motion of the motor to the drive shaft may be used or the drive shaft 26 and motor shaft may be specifically formed to complement one another and thus afford a direct connection.

[0019] The stepping motors 32 per se are conventional. However, rather than the typical 200 steps per revolution characteristic of conventional stepper motors, the stepper motors hereof are designed for 180 steps per revolution. By half-stepping the motor, 1° of revolution may be obtained. Stepping motors 32 may be of the the manufactured by Superior Electric, Co., 383 Middle Street, Bristol, Connecticut, and identified as Model No. M062-BD-8501. As a consequence of the direct drive between the stepper motors and the drive shaft, it will be appreciated that the motors may be timed in-phase or out-of-phase to incrementally advance the drive shaft 26. In this manner also, electronic damping of the shaft may be applied to both ends of the shaft rather than to but one end, as in the prior art.

[0020] Referring now to Figure 3, an arrangement is illustrated wherein both motors are operated in series from a common power amplifier 40 and a power source 42. An appropriate timing signal can be supplied to the circuit, as well known to those of skill in this art, and is schematically illustrated at 44.

[0021] In Figure 4, the stepper motors 32 are driven in parallel through separate amplifiers 46 from a common power source 48. Timing signals may be provided the circuit as illustrated at 50. To provide asynchronous operation, a delay 52 may be provided and the delay may be variable, for example, by a variable delay control 54. Staggered or asynchronous operation of the stepper motors as illustrated in Figure 4 enables cancellation of the torsional fronts intermediate the ends of the shafts as the torsional fronts proceed from the stepper motors down the paper feed shaft.

[0022] Consequently, in each of the above-described embodiments, there is provided a servo-mechanism in a printer for advancing paper comprised of a long, slender shaft which is to be rotated in increments. In such shaft, torsional and acoustical effects become detrimental in response to high accelerations, particularly where the ratio of the shaft length to its diameter is at least 20 to 1. The present invention, therefore, couples each end of the shaft to a respective drive motor and energizes both motors to rotate the shaft through predetermined rotary increments to control the delay and response of one end of the shaft with respect to the other end. In this manner, the effects of torsional vibration in the shaft and consequent high acoustical noise levels, when employed in a printer, are effectively minimized or eliminated.

[0023] While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.

Claims

1. A servo mechanism having an elongate shaft (26), and including means (32) for rotating the shaft (26) incrementally, wherein the rotation means includes respective drive motors (32) coupled to each end of the shaft (26), and means for energising both said motors (32) to rotate said shaft (26) through predetermined rotary increments so as to control the delay in response of one end of said shaft (26) with respect to the other end.

2. A printer comprising a servo mechanism as claimed in Claim 1, wherein the elongate shaft (26) is a paper feed drive shaft (26) for the printer; wherein the printer comprises paper-engaging elements connected to and driven by said shaft (26); and wherein the pair of drive motors (32) are connected directly to the opposite ends of the drive shaft (26) for directly incrementing the drive shaft (26).

3. A printer comprising a paper feed drive shaft (26) for the printer; paper-engaging elements connected to and driven by said drive shaft (26); and a pair of drive motors (32) connected directly to the opposite ends of said drive shaft (26) for directly incrementing said drive shaft (26).

4. A printer according to Claim 2 or Claim 3, including means for operating said motors (32) in synchronization with one another.

5. A printer according to Claim 2 or Claim 3, including means for operating said motors (32) out of phase with one another.

6. A printer according to any one of Claims 2 to 5, wherein the operating means includes a circuit having an amplifier for each motor and means for generating a timing signal coupled to said circuit.

7. A printer according to any one of Claims 2 to 6, wherein each of said motors (32) advances said shaft (26) in increments of substantially 1° of rotation.

8. A printer according to any one of Claims 2 to 7, including a tractor assembly having paper-engaging elements, said drive shaft (26) being carried by said tractor assembly.

9. A method of operating a servo or a printer as claimed in any one of the preceding claims, including energizing both said motors (32) simultaneously, to rotate the shaft (26) through a single predetermined rotary increment.

10. A method of operating a servo or a printer as claimed in any one of the claims 1 to 8, including energizing both said motors (32) sequentially, to incrementally rotate the drive shaft (26).

Drawing