MATERIAL HANDLING VEHICLE AND METHOD FOR CALCULATING A POSITION OF A CENTRE OF GRAVITY

Abstract

 Material handling vehicle (1), wherein the vehicle comprises, a control unit (2), a load surface comprising a first and a second section (4, 5), a first, second and third sensor device, wherein the material handling vehicle (1) is able to detect the position of the centre of gravity in a predetermined z-direction. The disclosure is also related to a method of determining a position of the centre of gravity of a load (9), in a predetermined z-direction, and a computer software.

Description

[0001] The present invention is related to a material handling vehicle and a method of calculating a position of the centre of gravity according to the appended claims.

BACKGROUND

[0002] It is known to transport loads with automated guided vehicles. One document describing such an arrangement is WO201791596A1, which describes a mobile drive unit. The mobile drive unit is able to take measures in order to provide an improved stability of the mobile unit by shifting position of an inventory holder of the vehicle.

SHORT DESCRIPTION OF THE INVENTION

[0003] There is a problem with the prior art when transporting goods. The mobile unit seeks to shift the position of an inventory holder in order to improve the stability. Also dampers is used for this. However the system requires that complex mechanics is applied. Thus, there is an objective technical problem to improve existing material handling vehicles such that a simple construction is achieved that does not need a complex damping system.

[0004] In order to solve at least one of the above problems it is suggested a material handling vehicle, wherein the vehicle comprises, a control unit. The vehicle also comprises a load surface. The load surface is also comprising a first section and a second section. The sections are separated by a predetermined length. The vehicle also comprises a first and a second sensor device for determining a force in a predetermined z-direction on the respective first and second section in a respective point of the first and second sections. It is preferred that the z-direction is the vertical direction. The vehicle also comprises a third sensor device for determining the acceleration of the material handling vehicle in a predetermined x-direction. The first sensor device is arranged such as to detect a first force in the z-direction at a point of the first section of the load surface. The second sensor device is arranged such as to detect a second force in the z-direction at point of the second section of the load surface. The control unit is arranged such that it is able to receive input from the first sensor device, the second sensor device and the third sensor device. The control unit further is arranged to determine a first state when the material handling vehicle is not in an accelerated state by receiving a sensor input from the third sensor device indicating a non-accelerated state.

[0005] The first state determines first values of the first force and the second force. The control unit further is arranged to determine a second state, when the material handling vehicle is in an accelerated state. The control unit performs this by receiving an input from the third sensor that indicates acceleration value. The second state determines second values of the first force and the second force in acceleration. The sum of the forces in a non-accelerated state, gives a value of the mass of a load carried on the respective first and second sections. Or the mass is a predetermined value that is given as an input value to the control unit. The control unit is arranged to use the difference in forces of the first forces, the second forces in respective state. The mass m of the load and the predetermined length, to determine the position in the z-direction of the centre of gravity of a load that is carried by the first section and the second section on said load surface. This is when the load is supported by said first section and said second section. It is preferred that the high point of the vehicle itself is the first and second section of the load surface. As an alternative the first and second sensors themselves constitute the high point of the vehicle.

[0006] The advantage of the above vehicle is that the safety of the vehicle can be improved. By determining the position of the centre of gravity in a predetermined direction, the drive properties of the combination of the vehicle and the load can be adapted. The vehicle can have its velocity optimized in for example turns and also in terms of brake distances. Also it will be possible to provide warnings or a general lower velocity if the position of the centre of gravity is not within a predetermined safety range. If as an alternative the mass of the load is given as a predetermined value, calculation can be further simplified, and faster.

[0007] As an alternative aspect there is suggested a material handling vehicle according to the above wherein the determination of the position of the centre of gravity in the predetermined direction is based on the formula,

[0008] Zpos is the position of the centre of gravity in the said z-direction of a load carried on the first section and the second section.

[0009] ΔR is the difference in values between non-accelerated and accelerated states of the first and second forces.

[0010] I is the length between the detected position of the first and second forces in the x-direction.

[0011] m is the mass of a load positioned on the first and second section of the load carrier surface.

[0012] a is the detected acceleration of the third sensor.

[0013] The advantage of performing the calculation according to the formula is that a very simple and fast calculation can be performed. A higher precision in the calculation is achieved. Also by the mathematical expression as simplified, very few variables are required in the calculation.

[0014] As an alternative aspect there is suggested a material handling vehicle the first sensor and the second sensor comprise strain gauges.

[0015] Strain gauges are simple and reliable. Also for a material handling vehicle operating in a very controlled environment of a warehouse, where the temperature is keep relatively constant, a strain gauge need not be recalibrated due to temperature variations. Also the strain gauge is rugged to its nature and will not be worn out by shocks and vibrations.

[0016] As an alternative aspect there is suggested a material handling vehicle said third sensor device comprise a first rotation sensor arranged to detect the rotation data of a wheel of the material handling vehicle. The first rotation sensor is arranged to send the first rotation data to the control unit wherein the first rotation data is used to determine acceleration of the material handling vehicle. Optionally the said wheel is a drive wheel.

[0017] By using a rotation sensor for determining the acceleration, no further sensor needs to be added to the vehicle. That is the rotation sensor is in general incorporated for other purposes in the material handling vehicle. Thus, a very efficient determination of the acceleration is achieved. The drive wheel is a wheel that comprises further mechanical equipment, and thus it is good position for a rotation sensor to be incorporated.

[0018] As an alternative aspect there is suggested a material handling vehicle according to the above, wherein the vehicle further comprises a second drive wheel. The third sensor device comprises a second rotation sensor that is arranged to detect a second rotation data of the second drive wheel and send the second rotation data to the control unit. The second rotation data is used to determine acceleration of the material handling vehicle in cooperation with first rotation data from said first rotation sensor. Optionally the vehicle comprises two drive motors that are individually controlled for allowing the two drive wheels of the material handling vehicle to steer the vehicle and change its direction in a horizontal plane.

[0019] With a second drive wheel the material handling vehicle is able to manoeuvre by running the drive wheels in different directions, and thus not requiring a steered wheel. Also a second rotation sensor is easily incorporated, in particular for a very precise determination of the acceleration.

[0020] As an alternative aspect there is suggested a material handling vehicle according to the above wherein the control unit is arranged to use rotation data from the rotation sensor or sensors to determine if the vehicle is turning, moving in a straight line or performing a turn.

[0021] By using input for determining the direction of movement of the material handling vehicle the precision in of movement of the vehicle can be improved.

[0022] As an alternative aspect there is suggested a material handling vehicle according to the above wherein the first and the second sections are provided with a lift device. Thus a load applied over both the first and the second sections is able to be lifted in vertical direction. Optionally the lift device is at least one hydraulic cylinder acting on the first and second sections. The lift device can comprise is at least one screw device acting on the first and second sections. The lift device may be a first lift device and a second lift device, applied to the respective first and second sections.

[0023] With a lift device the material handling vehicle can be use be operated by running under a load and then lifting the load from the ground. Thus, the vehicle can operate as a small pallet itself and transport loads in a warehouse. I can also enter into narrow spaces with low height.

[0024] As an alternative aspect there is suggested a material handling vehicle according the above wherein the lift device or lift devices is arranged to be used as the first and second sensors.

[0025] By using the lift device or devices as a way of detecting the reaction forces for the load, the material handling vehicle is very much simplified and sensors only for force detection is not required..

[0026] As an alternative aspect there is suggested a material handling vehicle according the above wherein the material handling vehicle is an automated guided vehicle with no forks as load surface.

[0027] An automated guided vehicle is different from a manually operated vehicle and can perform operations in a warehouse by itself. The automated guided vehicle comprises equipment for manoeuvring, without interaction from an operator. This provides for savings in terms of required operation personal and also the vehicle can operate without breaks. The advantages of the above is not achieved if forks constitutes the load surface.

[0028] As an alternative aspect there is suggested a material handling vehicle according to the above wherein further comprised is a further sensor device for detecting a further force in the predetermined direction. The further force is detected at a position separated from where the first and the second forces. This is done such that the three detected forces in the first state are corresponding to the mass of the load. The control unit is arranged to compare the forces of the respective sensor in the first and second state. Thus, the control unit is able to determine the position of the centre of gravity of the load also in three dimensions.

[0029] By incorporation of a further sensor the material handling vehicle can determine with precision the position for the centre of gravity of a load in all dimensions. Thus, achieving a very good base for further improving the operation of the material handling vehicle and preventing it from turning over.

[0030] As an alternative aspect there is suggested a material handling vehicle according the above a further sensor device is comprised for detecting a further force in the predetermined direction. The further force is detected at a position separated from where the first, the second forces and third forces. This is performed such that the four detected forces in the first state are corresponding to the mass of the load. The control unit is arranged to compare the forces of the respective sensor in the first and second state. Thus, the control unit is able to determine the position of the centre of gravity of the load also in three dimensions.

[0031] With a further force sensor the load can be positioned more freely and the accuracy is augmented in working conditions. The three dimensional accuracy determining of the centre of gravity is improved.

[0032] As an alternative aspect there is suggested a material handling vehicle according to wherein the third sensor device comprises an accelerometer.

[0033] By using an accelerometer as sensor for determining the acceleration, there is possible achieve a good determination of the acceleration without needing to consider for example slipping of the drive wheels to the support surface of the material handling vehicle.

[0034] There is also suggested a method for determining the position of the centre of gravity of a load carried by a material handling vehicle. The method comprising the step to position a load such that it is carried by a first and second section of a load surface of the material handling vehicle. The method comprises the step to determine that the material handling vehicle is in a non-accelerated state. The method further comprises the step to measure a first force of the first section of a load surface of the vehicle. The method further comprises the step to measure a first force of the second section of a load surface of the vehicle. The method further comprise the step to determine that the material handling vehicle is in an accelerated state. The method further comprises the steps to measure a second force of the first section of a load surface of the vehicle and to measure a second force of the second section of a load surface of the vehicle. The method further comprises the step to predetermine a length between the first and second section, i.e. the distance between the point where the first and second sensors engages the first and second sensors. The method also comprises the step to determine the mass of the load, or to use the mass of the load as a predetermined mass. The method also determine the acceleration of the vehicle in the accelerated state. The method also comprises the step to use the measured forces, acceleration and mass of the load to determine the position of the centre of gravity in a predetermined z-direction.

[0035] Optionally the method also comprises the step to perform a calculation using the predetermined length I between the first section and the second section of the load surface with the following formula,

wherein Zpos is the position of the centre of gravity in the said z-direction of a load carried on the first section and the second section of the load surface 3, wherein "ΔR" is the difference between first and second values of the first and second forces, wherein "a" is the detected acceleration, wherein "m" is the mass of the load.

[0036] The method provides for a simple and fast way for determining the position of the centre of gravity of a load on a material handling vehicle.

[0037] The advantage of using the formula has been described above.

[0038] As an alternative aspect there is suggested a method according to the above wherein the method further comprises the step to detect a third force at a position separated to the position of the detection of the first and second forces, wherein the measurement is performed at the first state and the second state. The method optionally further comprises the step to determine predetermined length between the first, second and third forces. The method further comprises the step to use the determined forces in a calculation where the horizontal position of a centre of gravity of the load is determined.

[0039] By a method as the above the precise position of the centre of gravity can be determined.

[0040] There is also disclosed a computer software according to claim 15.

[0041] The software allows for simple and efficient incorporation of the method into an existing material handling vehicle.

LIST OF DRAWINGS

[0042] 

Figure 1 discloses a material handling vehicle of the disclosure in a non-accelerated state, carrying a load.

Figure 2 discloses the vehicle of figure 1 from above with the load removed.

Figure 3 discloses a material handling vehicle of figure 1 in an accelerated state.

Figure 4 discloses the material handling vehicle of the previous figures, but with a further sensor for detection of the centre of gravity in three dimensions, the vehicle is in a non-accelerated state.

Figure 5 discloses the vehicle of Fig. 4 but in an accelerated state.

Figure 6 discloses a vehicle where an even further sensor is added for redundancy in measurement of forces.

Figure 7 discloses the vehicle of Fig. 6.

Figure 8 discloses a load and the centre of gravity and its position in three dimensions.

Figure 9 discloses a flow chart of the method according to the disclosure.

Figure 10, setting up a torque equation.

DETAILED DESCRIPTION

[0043] The present disclosure is related to a material handling vehicle. The material handling vehicle is in general an electric vehicle that is operating indoors, for example in a warehouse. The material handling vehicle may in particular an automated guided vehicle, also named AGV. The vehicle in general has a load surface. With load surface is meant a surface on which a load can be carried. In general the load surface may be an essentially flat surface, for example the top surface of a material handling vehicle. The present disclosure is not related to a fork-lift having a pair of forks as the load surface. The disclosure is also related to a material handling vehicle comprising at least two sensors. The sensors being able to determine the force of a load that has been positioned on a load surface. Force is meant the reaction force of the mass of a load. The load surface in general is divided into at least one first section and one second section. In general the first and second section can be flat with the load surface, or the first and second section can protrude above the load surface. The first and second sections are arranged such that a load carried on the vehicle will always cover the first and the second section. It should also be understood with the regard to the sections that these sections could also be one or several points. This means that the sensors could be one or two or more points, together defined as a section. If the section is an element it should in turn be carried on points where the sensors carry the section. It should also be understood that the first and second section can be a single element, carried by two or more sensors in points. Thus, the sections are not defined as being separate elements per se only. When discussion the length between the sections it should be understood that the definition of where the length begins and ends are the position of where force sensors detect in point like manner forces on the sections. With point is meant a limited area in the shape of a circle or the like. The circle can be of variating size, for example 1-20 mm in size.

[0044] In the below there is discussed for all aspects a passion for a centre of gravity of a load. The position should be understood to mean a point inside the load, where the centre of gravity is positioned. For some aspects there is not a point, but a position on a plane or e on a line. Thus, the position may be determined as a measurable distance to a plane in which plane the centre of gravity is positioned. It may also be on a line on which the centre of gravity may be positioned. It may also be a point that is determined in from all directions. The present disclosure does not determine the position in terms of centimetres, millimetres or meters, it is within the common knowledge of the skilled person to make this determination if needed.

[0045] Fig. 1 discloses a material handling vehicle 1 according to the disclosure. The material handling vehicle 1 is disclosed with a load 9 positioned on the vehicle 1. The vehicle 1 has a basic flat shape with a load surface 3. The vehicle 1 also comprises a wheel 11. The wheel 11 is a drive wheel. A further drive wheel 17 is also comprised on the other side of the vehicle 1, see Fig. 2. The drive wheels 11, 17 are powered wheels, that is they may be powered by a drive motor, preferably one for each drive wheel. The drive wheels 11, 17 may thus be powered by a respective drive motor 12, 18, in general an electric motor. The drive motors 12, 18 are individually controllable by the control unit 2, in this way the material handling vehicle 1 can manoeuvre, by for example inducing a turn through applying different rotation velocities to the respective drive wheel 11, 17. It should be understood that it is possible to have only one centrally positioned drive wheel, with one drive motor. This mono drive wheel could be steerable. In this case one rotation sensor is applicable. There is also disclosed a swivel wheel 14a in Fig. 1. There can be more than one swivel wheel, see fig 1, 14b.

[0046] A control unit 2, Fig.1 and Fig. 3, is comprised on the material handling vehicle 1. The control unit 2 is to be understood as being a main computer on the material handling vehicle 1. The control unit 2 thus comprises processors and memory for the vehicle. The control unit 2 has thus the ability to store and execute software stored on the memory of the control unit 2. The control unit 2 is arranged to be able to receive sensor input, in particular from the first, second and third sensors as discussed below. The control unit 2 may be composed by several sub-control units with different specific locations on the vehicle 1.

[0047] The load surface 3 is basically the upper side of the vehicle as seen in Fig.2 and 3. The material handling vehicle 1 is thus arrange for carrying a load on its "back". The load surface 3 is provided with a first section 4 and a second section 5. The first and second sections 4, 5 are positioned at a distance I from each other. The load 9 is supported by the first section 4 and the second section 5. The sections are disclosed in Fig. 2 as being two bar like section of the load surface 3. It should be understood that the first and second sections 4, 5 may have any appropriate shape. It is thinkable to that the first and second section is constituted by a respective half of the load surface 3, i.e. a load surface 3 divided by the middle in a front and back section, for example. The first section 4 and the second section 5 are separated by a distance "I". The distance "I" is predetermined, i.e. the distance is stored in the memory of the control unit 2. The distance "I" is disclosed in Fig. 2 as the distance between the centre of the first section 4 and the centre of second section 5. It is preferred that the first and the second sections 4, and 5 protrude a small bit above the other parts of the load surface 3. This allows for better determination of the forces Ra, Rb etc. as discussed below. It should be understood that that for the disclosure the distance "I" fully correspond to the engagement points for the load mass. That is in these points the full mass of the load is carried.

[0048] With regard to the present disclosure the material handling vehicle 1 is defined in relation to a predetermined z-direction. As a general definition the z-direction is the primary predetermined direction. The z-direction is meant to be a vertical direction. In general this is thus perpendicular to the load surface 3. It should be understood that smaller deviations from the vertical direction is possible for the predetermined z-direction.

[0049] There are also a predetermined x-direction, which correspond to the direction in longitudinal direction of the material handling vehicle 1. This can be seen in Fig. 2 as being from left to right in the Figure. This means that the longitudinal direction, the predetermined x-direction is the same as the direction from left to right also in Fig. 1 and Fig. 3.

[0050] The predetermined y-direction is to be construed as the transversal direction of the material handling vehicle 1. In Fig. 2 this is the direction from the bottom to the top of Fig.2. This is also disclosed in Fig. 8, view 32.

[0051] The material handling vehicle 1 also comprises a first sensor device 6. The first sensor device 6 may be a strain gauge. It may also be any other force sensor type. The first sensor device 6 is arrange to detect a force Ra, i.e. corresponding to a portion of the mass of a load 9, that is positioned on the first section. The force Ra is detected in a z-direction, that is the force Ra is thus a reaction force of a portion of the mass of a load 9 that is positioned on the first 4 and the second sections. The z-direction is as disclosed in Fig. 1 the vertical direction. The first sensor device 6 is arranged in association with the first section 4, in order to measure the force Ra on the first section in z-direction. The first sensor 6 thus engages the full mass of the load on the first section, in a point. Thus, the load mass applied to the first section is entirely carried on the first sensor 6.

[0052] The material handling vehicle 1 also comprises a second sensor device 7. The second sensor device 7 may be also be a strain gauge. It may also be any other force sensor type. The second sensor device 7 is arrange to detect a reaction force Rb, corresponding to a part of a mass of a load 9 that is positioned on the second section 5. The force Rb is detected in a z-direction. The z-direction is as disclosed in Fig. 1 essentially the vertical direction. The second sensor device 7 is arranged in association with the second section 5, in order to measure the force Rb on the second section in z-direction. The first sensor 7 thus engages the full mass of the load on the second section, in a point. Thus, the load mass applied to the first section is entirely carried on the first sensor 7.

[0053] Thus, the distance "I" is to be understood to be between the engagement points of the first and second sensors 6, 7.

[0054] Fig. 1 discloses a first state of the material handling vehicle 1. The control unit 2 is arranged such that it can detect that the material handling vehicle 1 is in this first state. The first state means that the material handling vehicle 1 is not accelerating, i.e. it is either standing still or moving in a straight line with constant speed. The determination of the first state may be performed by using a rotation sensor 13 on the first drive wheels 11, see Fig. 1 and 2. There may also be a second rotation sensor 18 applied to a second drive wheel 17. If the first rotation sensor 13 detects no altering rotation it can be determined that the vehicle 1 is in the first state. An even better determination can be achieved if rotation data from both a first rotation sensor 13 and a second sensor 18. In this case thus, these rotation sensors 13, 18 detects the same rotation and no change in rotation between wheel 11 and 17 the first state can be determined. Thus, the first state also comprises the case where on or more of the rotation sensors 13, 18 do not detect any rotation. If the material handling vehicle 1 is provided with an accelerometer, the control unit 2 can address the accelerometer and determine that there is no ongoing acceleration for the moment, and thus no need for addressing rotation data is necessary and the data directly from the accelerometer may be used for determining that the vehicle 1 is in the first state.

[0055] It should be understood for the disclosure as a whole that the rotation sensor or sensors may be applied to other wheels than the drive wheels 11, 17. For example the mentioned swivel wheels 14a, b may have rotation sensors applied to them, or any other wheel that is applied to the material handling vehicle 1.

[0056] When the material handling vehicle 1 is in the first state the sum of forces Ra, and Rb corresponds to the mass of the load 9. It is of course so that if the material handling vehicle 1 is standing on a leaning support surface the Ra and Rb might be different. There is of course a prerequisite that the load 9 is only supported on the first section and the second section 4, 5, and thus not only supported on only one of these sections, i.e. that the load is only supported on the points where the first and second sensors 6, 7 is engaging the sections 6, 7. It is to be understood for the complete disclosure of any embodiment that the measuring of Ra, Rb can be controlled by the control unit 2, to be done when it is determined that the material handling vehicle 1 is in an essentially level, horizontal position. The determination of horizontal position may be performed in a known way by adding an angle sensor, or any other known way to the skilled person.

[0057] The control unit 2 is arranged to detect a second state. The second state of the material handling vehicle 1 is defined as when the vehicle is accelerating. The detection of the second state may be made by a third sensor as the detection of the first state. The third sensor is preferred to be the rotation sensor 13. The rotation sensor 13 may as said be applied to the wheel 11 as seen in Fig. 1, 2 or 3. The rotation sensor 13 thus is able to detect the rotation velocity of the wheel 11. The rotation sensor 13 determines rotation data that is sent to the control unit 2. By the detected rotation data the control unit 2 can for example determine angular velocity changes, which are transformed into an acceleration value. There may also be a second rotation sensor 18, Fig. 2. The second rotation sensor 18 has preferably the same detection ability as the first rotations sensor 13. By adding a second rotation sensor 18 it is possible to detect more precisely the acceleration of the material handling vehicle 1. For example the control unit 2 can compare the rotation data of the first and second 13, 18. The comparison is useful in determining that the material handling vehicle 1 is moving forward in a straight line, i.e. the predetermined x-direction. The second state is best determined when the material handling vehicle 1 is moving in and accelerated movement in parallel with the x-direction. In the second state the control unit determines the acceleration value "a" at the same time as the reaction forces Ra' and Rb'.

[0058] The control unit 2 is arranged to compare forces at the first section 4 in first and second state. A first force Ra in the first state is compared with a second force Ra' in the second state. I.e. the difference between Ra and Ra', ΔRa is determined. Likewise the control unit 2 is arranged to compare forces at the second section 5, i.e. a first force Rb and a second force Rb', i.e. ΔRb. The sum of the differences ΔRa is used in a calculation the determined mass m, and the determined acceleration in the second state and thus a value in z-direction of the position of the centre of gravity of the load 9, Fig. 1, may be determined. The position in z-direction can also be determined as the height of the centre of gravity as measured from the load surface 3, (i.e. the respective section 4 and 5). The calculation requires the length I between the first and the second sections, more precisely the position of the first and the second sensor device 6, 7. As state the load 9 most be supported by both the first 4 and second section 5 for this calculation to be correct.

[0059] It is preferred that the highest point for the material handling vehicle 1 is the first and second sections 4, 5. It is also possible that the first and second sections 4,5 are comprised in a plane that is common with the remaining part of the load surface 3. But for a general disclosure the load surface can be any surface which can carry a load.

[0060] It is also thinkable that the sensors 6, 7 and any further sensor are constituting the highest point.

[0061] The calculation of the z-position of the centre of gravity of a load 9, Fig. 1, Fig. 8, is preferred to be executed by the control unit 2 using the following formula:

[0062] The Zpos is thus the position of the centre of gravity in the z-direction. This can be translated as the distance from the load surface 3 to the centre of gravity, or the height of the centre of gravity over the load surface 3. ΔR is the already discussed force difference. "I" is the distance between the first section 4 and the second section 5, or more precisely the horizontal distance between the first sensor device 6 and the second sensor device 7. "m" is the mass of the load 9 as measured in the first state. Further "a" is the acceleration as measured in the second state.

[0063] The formula is taken from a torque calculation which is best seen in relation to Fig. 10. Wherein a torque calculation where the following calculation is made:
The First condition:

[0064] The Second condition

[0065] Which then can be reduced down to the formula 111 as disclosed above.

[0066] For the material handling vehicle 1 of Fig. 1-3 there are also a determination of position of the centre of the x-position of the load 9. As the difference between force Ra and Rb can be calculated and their sum is proportional to the total mass m. The position of the centre of gravity in x-direction may be determined. See also Fig. 8 ref no 30 and 32 which discloses a reference to the x-direction. Thus, both the position for a centre of gravity in in z-direction and x-direction may be determined with the material handling vehicle of Fig. 1-3. Thus, it can be seen as the position of the centre of gravity CG is determined to be on determined line extending in the transversal y-direction.

[0067] It should also be understood that even if TPx is related to the x-direction in Figs. 1, 4, 5, 6, 7 it is to be understood that if the sensor devices are positioned differently it is also possible to determine TPz. I.e. if TPy is determined, TPz can be determined, by a similar calculation as when using TPx, this calculation would require the distance between Ra and Rc in Fig. 4, 5, 6 which would be substituted for "I" in the above calculation.

[0068] For the above aspect there should be understood that the full mass of the load 9 is carried by the first and second sensor for determining the mass m of the load 9 in the first state. Or the mass of the load 9 is predetermined before the first state is determined, for example by weighing the load separately.

[0069] In a further development there can be incorporated a further sensor device 6c for detecting a force Rc, see Fig. 4. The position of the further sensor device 6c is preferred to be on the first section 4 i.e. but separated from the first sensor device 6 in the y-direction. But it should be understood that the further sensor device 6c may be positioned also on the second section 5, or even on an further third section (not shown). Thus, in this setup it is allowed for a more advanced calculation of the position of the centre of gravity of a load 9. By introducing a sensor device 6c that provides for a triangular relationship between force Ra, Rb and Rc, it is made possible to also determine the position of the centre of gravity of the load 9 in three dimensions. That is the position can be determined also in the y-direction. In order to perform this determination it is necessary to have the distance 25 between sensor device 6 and 6c, see Fig. 4 and 5. The distance y-coordinate of the centre of gravity may thus be calculated as with the calculation of TPz above but in the transversal direction, and where the distance 25 is given It should be understood that in order for this to function well the Rb sensor device 7, should not be too much off centre from a centre line of the vehicle in longitudinal direction (x-direction). E.g. if the sensor device 7 is positioned at a corner or close to the side 40 or 42 as seen in Fig 2, the load 9 risk to overturn or have parts if its mass to be carried by a point closer to the side 40 of the vehicle and thus the calculations would not be correct for the z-position, TPz of the load 9. If this condition is fulfilled the mass of the load 9 can be determined in a calculation of adding Ra, Rb and Rc together.

[0070] The material handling vehicle 1 may comprise a lift device 15, 16, Fig. 1, in general a first and second lift device, at the first and second sections 4, 5. The lift devices 15, 16 may in general be a hydraulic cylinder acting on the first and second sections 4, 5. The lift devices 15, 16 may be used for lifting a load 9 when a material handling vehicle 1 has entered under a load 9. The lift devices 15, 16 can also be a screw device or a hydraulic cylinder. The lift devices may thus life the load in a parallel manner in four points for example, thus giving a lifting situation and force distribution as disclosed in Figs. 6-7. In general there is a tandem function of the first section 4 and the second section 5, that is in lifting, i.e. the first section 4 is lifted at the same speed and height as the second section 5. In a further development the first and second lift devices 15, 16 may take the position as the first and second sensor 6, 7 device. I.e. the lift devices themselves functions as sensors for detecting the reaction forces Ra, Rb etc. of a load that is carried by the first and second sections, 4, 5.

[0071] The material handling vehicle 1 is preferred to be an AGV, an automated guided vehicle. This it is not operated manually by an operator.

[0072] Fig. 6 and Fig. 7 disclose a variant of the material handling vehicle 1 where an even further sensor 7d is applied. With four sensor 6, 6c, 7, 7d the load 9 the setup is static and the first state is fully determined. The position of the load 9 on the vehicle 1 can be varied as long as all four points, i.e. corresponding to the sensors fully carry the load 9. Thus, the load 9 does not risk to overturn. As the four points carry the load 9 the mass m of the load 9, if not being predetermined, can be determined in a simple calculation of adding the forces Ra, Rb, Rc and Rd together. Thus, there are four force sensors applied to the vehicle 1. The disclosed position are disclosed on the first and second sections 4, 5, but it is of course also possible to partition the load surface 3 into four individual sections on which a load 9 is to be positioned, or the vehicle has a single section, carried by all sensors Each of these individual sections should then have the same features and properties as the first and second sections 4, 5, i.e. each section having an own sensor 6, 6c, 7 and 7d. By having four sensors a redundancy can be introduced into the calculation of the position of the load's centre of gravity. Thus, the control unit 2 may compare two different calculations using a group of three sensors for example sensors 6, 6c, and 7 with a second group of sensors, such as 6, 7 and 7d. When determining the first state the system should be calibrated, such that the mass "m" is correctly determined. If there are further sections used, i.e. more than two, 4, 5 the sum of the detected forces of the individual sections must be added, in order to achieve a precise determination of the mass "m" of a load 9. Thus, this aspect will provide a redundant and more precise determination of the x, y, and z position of the centre of gravity of a load, see also Fig. 8.

[0073] The number of force sensors is not limited to four sensors, 6, 6c, 7, 7c. Any number of sensors could be used, but for the calculation the load must be carried by a detectable number of sensors. On number of force sensors could be six.

[0074] For all sensor devices both discussed above and below, it is mandatory that the load 9 is only carried by the sensor devices, either by direct point contact with the load itself, or in that the sensors are in contact with a plate, or the like, in a direct point contact, on which plate the load 9 is positioned. I.e. as the skilled person is aware of it is not possible to determine the mass m of the load 9 if a part of its mass m is carried by a further point that lacks a sensor. It is also thinkable that the mass m is given as input to the control unit (2) of the vehicle, where the mass m has been predetermined for example in a weighing station in a warehouse.

[0075] The disclosure is also related to a method for determining the position of the centre of gravity of a carried load 9 of a material handling vehicle 1, see Fig. 9. The method comprises the steps A-.:
Step A: position a load 9 such that it is carried by a first and second section 4, 5 of a load surface 3 of the material handling vehicle 1.

[0076] Step A is an important requirement as it will be difficult to perform the determination of the position of the centre of gravity if not both sections 4, 5 are supporting the load 9.

Step B: determine that the material handling vehicle 1 is in a non-accelerated state.

Step C: measure a first force Ra of the first section 4 of a load surface 3 of the vehicle.

Step D: measure a first force Rb of the second section 5 of a load surface 3 of the vehicle 1.

[0077] Steps B, C and D are a required in order to detect the mass m of a load 9.

Step E: determine that the material handling vehicle 1 is in an accelerated state.

Step F: measure a second force Ra' of the first section 4 of a load surface 3 of the vehicle.

Step G: measure a second force Rb' of the second section 5 of a load surface 3 of the vehicle 1.

[0078] In order to determine the position of a load's centre of gravity in the predetermined z-direction it is required to measure forces and acceleration in an accelerated state.

[0079] Step H: predetermine a length I between the first and second section 4, 5. I.e. distance between the point where the first and second sensors (6, 7) engages the first and second sensors (6, 7),

[0080] The length "I" is needed in the calculation of the position of the centre of gravity.

Step I: determine the mass m of the load 9.

Step J: determine the acceleration a of the vehicle 1 in the accelerated state.

Step K: use the measured forces, acceleration and mass of the load to determine the position of the centre of gravity in a predetermined z-direction.

[0081] Thus, a material handling vehicle 1 can be modified and thus used the above method steps A-K in order to perform the method.

[0082] The method can be improved applying further step L:
Step L: perform a calculation using the predetermined length I between the first section (4) and the second section (5) of the load surface (3) with the following formula,

wherein Zpos is the position of the centre of gravity in the said z-direction of a load carried on the first section (4) and the second section (5) of the load surface 3,

[0083] This formula is very easily to upload to a control unit 2 of a material handling vehicle 1.

[0084] It is also possible to improve the method by applying further steps. Thus, the method according to the above, wherein the method may comprises the steps M-O:
Step M: detect a third force Rc at a position separated to the position of the detection of the first and second forces Ra, Rb, wherein the measurement is performed at the first state and the second state.

[0085] Step M provides for a more precise determination of the position of centre of gravity of a load 9.

Step N: determine predetermined length between the first, second and third forces Ra, Rb, Rc.

Step O: use the determined forces Ra, Rb, Rc in a calculation where the horizontal position x, y of a centre of gravity of the load 9 is determined.

[0086] This determination is thus precisely determining the position of a centre of gravity of a load, see Fig. 8.

[0087] The disclosure is also related to a computer software that when stored on and executed on a control unit of a material handling vehicle performs the method according to the above. Thus, it is possible to modify an existing material handling vehicle if there are the required sensor data available, in a simple and efficient way.

Claims

1. Material handling vehicle (1), wherein the vehicle comprises,
a control unit (2),
a load surface (3) of the material handling vehicle (1) comprising a first section (4) and a second section (5), wherein the sections (4, 5) are separated by a predetermined length (I),
a first and a second sensor device (6, 7) for determining a force in a predetermined z-direction on the respective first and second section (4, 5) in a respective point of the first and second sections, preferably the z-direction is the vertical direction,
a third sensor device for determining the acceleration of the material handling vehicle (1) in a predetermined x-direction,
wherein the first sensor device (6) is arranged such as to detect a first force (Ra) in the z-direction at a point of the first section (4) of the load surface (3),
wherein the second sensor device (7) is arranged such as to detect a second force (Rb) in the z-direction at point of the second section (5) of the load surface (3),
wherein the control unit (2) is arranged such that it is able to receive input from the first sensor device (6), the second sensor device (7) and the third sensor device,
wherein the control unit (2) further is arranged to determine a first state when the material handling vehicle (1) is not in an accelerated state by receiving a sensor input from the third sensor device indicating a non-accelerated state,
wherein the first state determines first values of the first force (Ra) and the second force (Rb),
wherein the control unit (2) further is arranged to determine a second state when the material handling vehicle (1) is in an accelerated state by receiving an input from the third sensor that indicates acceleration value (a),
wherein the second state determines second values of the first force (Ra') and the second force (Rb') in acceleration,
wherein the sum of the forces (Ra, Rb) in a non-accelerated state, gives a value of the mass (m) of a load (9) carried on the respective first and second sections (4, 5) or the mass (m) is a predetermined value that is given as an input value to the control unit (2),
wherein the control unit (2) is arranged to use the difference in forces (ΔR) of the first forces (Ra; Ra'), the second forces (Rb; Rb') in respective state, the mass (m) of the load (9) and the predetermined length (I), to determine the position in the z-direction (z) of the centre of gravity (CG) of a load (9) that is carried by the first section (4) and the second section (5) on said load surface (3) and being supported by said first section (4) and said second section (5),
preferably the high point of the vehicle itself is the first and second section (4, 5) of the load surface (3) or the first and second sensors themselves constitute the high point of the vehicle (1).

2. Material handling vehicle (1) according to claim 1, wherein the determination of the position of the centre of gravity in the predetermined direction is based on the formula,

wherein Zpos is the position of the centre of gravity (CG) in the said z-direction of a load (9) carried on the first section (4) and the second section (5),

where ΔR is the difference in values between non-accelerated and accelerated states of the first and second forces (Ra, Rb; Ra', Rb'),

wherein I is the length between the detected position of the first and second forces (Ra, Rb) in the x-direction,

wherein m is the mass of a load positioned on the first and second section of the load carrier surface,

wherein a is the detected acceleration of the third sensor.

3. Material handling vehicle (1) according to claim 1 or 2, wherein the first sensor (6) and the second sensor (7) comprise strain gauges.

4. Material handling vehicle (1) according to any of the claims above, wherein said third sensor device comprise a first rotation sensor (13) arranged to detect the rotation data of a wheel (11) of the material handling vehicle (1), and the first rotation sensor (13) is arranged to send the first rotation data to the control unit (2) wherein the first rotation data is used to determine acceleration (a) of the material handling vehicle (1), preferably said wheel (11) is a drive wheel.

5. Material handling vehicle (1) according to claim 4, wherein the vehicle (1) further comprises a second drive wheel (17) and wherein the third sensor device comprises a second rotation sensor (19) that is arranged to detect a second rotation data of the second drive wheel (17) and send the second rotation data to the control unit (2), wherein the second rotation data is used to determine acceleration (a) of the material handling vehicle (1) in cooperation with first rotation data from said first rotation sensor (13), preferably vehicle (1) comprises two drive motors (12, 18) that are individually controlled for allowing the two drive wheels (11, 17) of the material handling vehicle (1) to steer the vehicle (1) and change its direction in a horizontal plane.

6. Material handling vehicle (1), according to any of the claims 4-5, wherein the control unit (2) is arranged to use rotation data from the rotation sensor (13) or sensors (19) to determine if the vehicle (1) is turning, moving in a straight line or performing a turn.

7. Material handling vehicle (1) according to any of the claims above, wherein the first and the second sections (4, 5) are provided with a lift device (15, 16), such that a load (9) applied over both the first and the second sections (4, 5) is able to be lifted in vertical direction, preferably the lift device (15, 16) is at least one hydraulic cylinder acting on the first and second sections and/or the lift device (15, 16) is at least one screw device acting on the first and second sections (4, 5) and/or the lift device (15, 16) is a first lift device (15) and a second lift device (16), applied to the respective first and second sections (4, 5).

8. Material handling vehicle (1) according to claim 7, wherein the lift device or lift devices (15, 16) is arranged to be used as the first and second sensors (6, 7).

9. Material handling vehicle (1) according to any of the claims above, wherein the material handling vehicle (1) is an automated guided vehicle with no forks as load surface.

10. Material handling vehicle (1) according to any of the claims above, wherein further comprised is a further sensor device (6c) for detecting a further force (Rc) in the predetermined direction (z), wherein the further force (Rc) is detected at a position separated from where the first and the second forces (Ra, Rb), such that the three detected forces in the first state (Ra, Rb and Rc) are corresponding to the mass (m) of the load (9), wherein the control unit (2) is arranged to compare the forces (Ra, Rb, Rc,) of the respective sensor in the first and second state, and thus the control unit (2) is able to determine the position of the centre of gravity of the load (9) also in three dimensions (x, y, z).

11. Material handling vehicle (1) according to claim 10, wherein a further sensor device (7d) is comprised for detecting a further force (Rd) in the predetermined direction (z), wherein the further force (Rd) is detected at a position separated from where the first, the second forces and third forces (Ra, Rb, Rc), such that the four detected forces in the first state (Ra, Rb, Rc and Rd) are corresponding to the mass (m) of the load (9), wherein the control unit (2) is arranged to compare the forces (Ra, Rb, Rc, Rd) of the respective sensor in the first and second state, and thus the control unit (2) is able to determine the position of the centre of gravity of the load (9) also in three dimensions (x, y, z).

12. Material handling vehicle of any of the claims 1-2 or 6-11, wherein the third sensor device comprises an accelerometer.

13. Method for determining the position of the centre of gravity of a carried load (9) of a material handling vehicle (1), comprising the steps of:

A: position a load (9) such that it is carried by a first and second section (4, 5) of an load surface (3) of the material handling vehicle (1),

B: determine that the material handling vehicle (1) is in a non-accelerated state,

C: measure a first force (Ra) of the first section (4) of a load surface (3) of the vehicle,

D: measure a first force (Rb) of the second section (5) of a load surface (3) of the vehicle (1),

E: determine that the material handling vehicle (1) is in an accelerated state,

F: measure a second force (Ra') of the first section (4) of a load surface (3) of the vehicle,

G: measure a second force (Rb') of the second section (5) of a load surface (3) of the vehicle (1),

H: predetermine a length (I) between the first and second section (4, 5), i.e. the distance between the point where the first and second sensors (6, 7) engages the first and second sensors (6, 7),

I: determine the mass (m) of the load (9) or the step of using the mass (m) as a predetermined value,

J: determine the acceleration (a) of the vehicle (1) in the accelerated state,

K: use the measured forces, acceleration and mass of the load to determine the position of the centre of gravity in a predetermined z-direction, preferably

the method comprises the step of:
L: perform a calculation using the predetermined length I between the first section (4) and the second section (5) of the load surface (3) with the following formula,

wherein Zpos is the position of the centre of gravity in the said z-direction of a load carried on the first section (4) and the second section (5) of the load surface 3,

wherein "ΔR" is the difference between first and second values (Ra, Rb; Ra', Rb') of the first and second forces,

wherein "a" is the detected acceleration,

wherein "m" is the mass of the load.

14. Method according to claim 13, wherein the method further comprises the steps of:

M: detect a third force (Rc) at a position separated to the position of the detection of the first and second forces (Ra, Rb), wherein the measurement is performed at the first state and the second state,

N: determine predetermined length between the first, second and third forces (Ra, Rb, Rc),

O: use the determined forces (Ra, Rb, Rc) in a calculation where the horizontal position (x, y) of a centre of gravity of the load (9) is determined.

15. Computer software that when stored on and executed on a control unit of a material handling vehicle performs the method according to any of the claims 13-14.

Drawing