Auto guide vehicle

An auto guide vehicle (20) that conveys a cart (10), wherein the auto guide vehicle (20) is provided with: a fluid pressure cylinder (22) that is able to be extended and retracted vertically, and that applies an upward pressing force to the floor surface of the cart (10); a fluid pressure supply device (70) that supplies a fluid to the fluid pressure cylinder (22); pressure regulating means (50) that regulates the fluid pressure of the fluid supplied from the fluid pressure supply device (70) to the fluid pressure cylinder (22); a control board (40) that outputs a fluid pressure command value to the pressure regulating means (50); and a pressure sensor (100) that detects the fluid pressure of the fluid supplied to the fluid pressure cylinder (22); wherein the control board (40) computes derivatives of the fluid pressure detected by the pressure sensor (100), estimates a timing at which the cart begins to leave the ground based on a pattern of the computed derivatives, and computes the command value by multiplying a coefficient less than one by the fluid pressure detected by the pressure sensor (100) at the estimated timing.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the National Stage entry of PCT/JP2018/017112, filed on Apr. 27, 2018, which claims priority to Japan Application Number 2017-087864, filed on Apr. 27, 2017, which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention relates to an auto guide vehicle. Specifically, the present invention relates to an auto guide vehicle that can stably transport a cart.

BACKGROUND ART

Patent Document 1 discloses a towing system in which a cart is coupled by pin-coupling to and towed by an auto guide vehicle (hereinafter abbreviated to AGV) that moves autonomously along guide paths provided on the floor surface of an assembly factory in order to transport components to assembly lines in the factory. In other words, this towing system involves providing coupling grooves in the bottom surface of a cart, and with the AGV ensconced under the floor of the cart, having the AGV couple with the cart by inserting coupling pins into the coupling grooves in the cart. Similar technologies are also disclosed in Patent Documents 2 and 3.

Patent Document 4 discloses technology in which an AGV is ensconced underneath a wagon and the wagon is completely lifted up with a lift device provided in the AGV. The lifted wagon is in a state in which the wheels have left the floor surface.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

As described in Patent Documents 1, 2, and 3, a towing system involves modifying the bottom surfaces of carts to provide coupling grooves, thus increasing costs. Such cost increases are particularly significant in factories and product distribution centers in which there is a need to modify large numbers of carts. Additionally, in the case of towing systems, there was a need to make the AGV bodies heavy to keep the drive wheels from slipping.

In technologies in which the cart is completely lifted by a lift device provided in the AGV, as in Patent Document 4, the wheels of the cart leave the floor surface, so there was a risk of the cart tipping over if the cargo in the cart was unbalanced.

Therefore, the present inventors have proposed a related application (Japanese Patent Application No. 2015-255945).

In this related application, the weight balance remains unknown until the cart is completely lifted by approximately 20 mm and an upper-end limit switch of an air cylinder switches on.

For this reason, unless the air cylinder is moved so that a receiving plate that contacts the cart is made horizontal, there is a possibility that the cart will lean considerably, or the cargo on the cart will collapse.

Additionally, even if the weight is unbalanced, the air cylinder must be lifted to the maximum stroke, so there is a need to select the maximum load that can be expected to be applied to a single air cylinder and the pressure to be supplied to the air cylinder in order to lift the maximum load.

Solution to Problem

An auto guide vehicle according to claim1of the present invention, which solves the abovementioned problem, is an auto guide vehicle that conveys a cart by being ensconced in a standard space formed between a floor surface and a bottom surface of the cart, wherein the auto guide vehicle is provided with: a fluid pressure cylinder that is able to be extended and retracted vertically, and that applies an upward pressing force to the floor surface of the cart; a fluid pressure supply device that supplies a fluid to the fluid pressure cylinder; pressure regulating means that regulates the fluid pressure of the fluid supplied from the fluid pressure supply device to the fluid pressure cylinder; a control board that outputs a fluid pressure command value to the pressure regulating means; and a pressure sensor that detects the fluid pressure of the fluid supplied to the fluid pressure cylinder; wherein the control board comprises a differentiation circuit that computes derivatives of the fluid pressure detected by the pressure sensor; an estimation circuit that, based on a pattern of the derivatives computed by the differentiation circuit, estimates a timing at which the cart begins to leave the ground; and a coefficient multiplication circuit that computes the command value by multiplying a coefficient less than one by the fluid pressure detected by the pressure sensor at the timing estimated by the estimation circuit.

An auto guide vehicle according to claim2of the present invention, which solves the abovementioned problem, is an auto guide vehicle as in claim1, wherein: the fluid pressure cylinder is formed by inserting a piston into a cylinder body so as to be able to move vertically, a receiving plate that contacts the bottom surface of the cart is provided on an upper end of a piston rod connected to the piston, and a proximity switch that switches on upon approaching to within a certain distance from the floor surface of the cart is provided on the receiving plate; and the estimation circuit estimates the timing at which the cart begins to leave the ground as being a time at which, with the proximity switch switched on, the derivative computed by the differentiation circuit has risen to a first prescribed value or higher, then fallen to a second prescribed value or lower.

An auto guide vehicle according to claim3of the present invention, which solves the abovementioned problem, is an auto guide vehicle as in claim1, wherein the estimation circuit estimates the timing at which the cart begins to leave the ground as being a time at which, after a certain period of time has elapsed since the fluid pressure cylinder began to extend, the derivative computed by the differentiation circuit has risen to a first prescribed value or higher, then fallen to a second prescribed value or lower.

An auto guide vehicle according to claim4of the present invention, which solves the abovementioned problem, is an auto guide vehicle as in claim1, wherein the estimation circuit estimates the timing at which the cart begins to leave the ground as being a time at which the derivative computed by the differentiation circuit becomes approximately zero.

An auto guide vehicle according to claim5of the present invention, which solves the abovementioned problem, is an auto guide vehicle as in claim1, wherein, when there are multiple fluid pressure cylinders, the pressure regulating means and the pressure sensor are respectively provided on respective fluid pressure cylinders; and the coefficient multiplication circuit respectively outputs, to the respective pressure regulating means, command values corresponding to the pressures detected by the respective pressure sensors.

Advantageous Effects of Invention

In the auto guide vehicle of the present invention, the fluid pressure of a fluid supplied to a fluid pressure cylinder is detected by a pressure sensor, the derivative of the detected fluid pressure is computed by a differentiation circuit, the timing at which a cart begins to leave the ground is estimated by an estimation circuit based on the pattern of derivatives computed by the differentiation circuit, a coefficient less than one is multiplied, by a coefficient multiplication circuit, with the fluid pressure detected by the pressure sensor at the timing estimated by the estimation circuit, and the resulting value is output as a command value from a control board to a pressure regulating means. Thus, a fluid having a fluid pressure regulated by the pressure regulating means is supplied from a fluid pressure supply device to a fluid pressure cylinder, so that the total weight of the cart and the cargo loaded on the cart is distributed and supported not only by the wheels of the auto guide vehicle, but also by the wheels on the cart, thus allowing the cart to be stably transported.

DESCRIPTION OF EMBODIMENTS

Hereinbelow, the present invention will be explained in detail with reference to the embodiments shown in the drawings.

The AGV according to the first embodiment of the present invention is illustrated inFIGS. 1 to 4.

As illustrated inFIGS. 1 and 2, an AGV20according to the present embodiment transports a cart10having multiple cargo items30on the upper surface thereof by being ensconced in a space underneath the bottom surface of the cart10. The cart10has a standard space between a floor surface1and a bottom surface2, and is provided with casters11as wheels at the four corners.

In the AGV20, two drive wheels23having a turning function and two driven wheels24are provided on a vehicle body21that is lower than the space in the cart10. Furthermore, air cylinders22that apply an upward pressing force to the bottom surface2of the cart10are installed at four locations to the left, right, front and rear.

The air cylinders22are able to be extended and retracted vertically, and horizontal receiving plates25are installed on the upper ends of front and rear air cylinders22. In other words, two receiving plates25are provided, to the left and the right.

Therefore, when the air cylinders22are extended, the receiving plates25come into contact with the cart10, and an upward pressing force is applied to the bottom surface2of the cart10by the receiving plates25.

With the AGV20of the present embodiment, as long as the weight is within a set upper-limit carrying weight, if the air cylinders22are raised to the upper ends, the casters11of the cart10will leave the floor surface. On the other hand, if the air cylinders22are lowered to the lower ends, the casters11of the cart10will be grounded on the floor surface.

A compressed air supply device for supplying compressed air (air) to the air cylinders22and pressure regulating means for regulating the pressure of the compressed air supplied to the air cylinders22will be explained with reference toFIG. 3.FIG. 3relates to the two front air cylinders22. The two rear air cylinders22are similarly configured, so their explanations will be omitted.

As illustrated inFIG. 3, an air cylinder22is formed by inserting a piston222into a cylinder body221so as to be able to move vertically, and providing a stopper223for stopping the rising of the piston222at the upper end of the cylinder body221. Furthermore, a piston222is connected to the lower end of the piston rod224, which penetrates through the stopper223. A receiving plate25for contacting the bottom surface of the cart10is installed on the upper end of the piston rod224.

A proximity sensor225is provided on the upper surface of the receiving plate25. The proximity sensor225switches on upon approaching close enough to the bottom surface of the cart10to come into contact therewith, and switches off upon withdrawing to a certain distance from the bottom surface of the cart10. The on-off signals from the proximity sensor25are input, as sensor outputs, to a control board40, as indicated by the dashed lines.

The cylinder body221is divided into two air chambers A, B by the piston222(in the drawing, A refers to the lower air chamber and B refers to the upper air chamber). An electropneumatic regulator50, an air tank60, and an air compressor70are connected, in this order, to the air chamber A, and a depressurization valve80and a solenoid valve90are connected, in this order, to the air chamber B.

Additionally, a pressure sensor100is attached between the air chamber A and the electropneumatic regulator50. The pressure sensor100detects the pressure of compressed air supplied from the electropneumatic regulator50to the air chamber A (hereinafter referred to as the pressure in the air cylinder22). The pressure detected by the pressure sensor100is input, as a sensor output, to the control board40.

The air tank60and the air compressor70are compressed-air supply devices. The air compressor70generates compressed air and the air tank60stores the compressed air that has been generated.

The electropneumatic regulator50is a pressure regulating means that regulates the pressure of the compressed air supplied to the air chamber A in the air cylinder22based on a command value by an output signal from the control board40. InFIG. 3, during the process of raising the piston222, compressed air flows as indicated by the black arrows in the drawing, and during the process of lowering the piston222, compressed air flows as indicated by the white arrows in the drawing.

The depressurization valve80, based on a command by an output signal (command value) from the control board40, reduces the pressure in the air chamber B of the air cylinder22, and a solenoid valve90, based on the output signal from the control board40, releases the compressed air to the atmosphere.

Output signals are sent from the control board40to the electropneumatic regulator50, the depressurization valve80, and the solenoid valve90, and input signals are sent from the electropneumatic regulator50to the control board40. These electrical signals are indicated by dashed lines inFIG. 3.

The electropneumatic regulator50, as illustrated inFIG. 4, is composed of a control circuit501, an air-supplying electromagnetic valve502, an air-discharging electromagnetic valve503, a pressure sensor504, and a branched pipe505.

The branched pipe505is provided with a pipe line505aconnected to the air cylinder22, a pipe line505bconnected to the air tank60, and a pipe line505cconnected to an air discharge system. The air-supplying electromagnetic valve502is provided between the pipe line505aand the pipe line505b. The air-discharging electromagnetic valve503is provided between the pipe line505aand the pipe line505c.

Therefore, when the air-supplying electromagnetic valve502is opened by the control circuit501, the pipe line505aand the pipe line505bare connected, and compressed air flows from the air tank60to the air chamber A in the air cylinder22. As a result thereof, the pressure in the air chamber A in the air cylinder22increases and the piston222rises.

Additionally, when the air-discharging electromagnetic valve503is opened by the control circuit501, the pipe line505aand the pipe line505care connected, and compressed air flows from the air cylinder22to an air discharge system. As a result thereof, the pressure in the air chamber A in the air cylinder22is reduced and the piston222lowers.

The pressure sensor504is connected to the pipe line505aand detects the pressure of the compressed air supplied to the air chamber A in the air cylinder22. The pressure detected by the pressure sensor504is converted to an output signal by the control circuit501and sent, as an input signal, to the control board40.

As an input signal, the control circuit501is supplied with an output signal from the control board40, and based on the pressure detected by the pressure sensor504, regulates the pressure of the compressed air supplied to the air chamber A in the air cylinder22by opening and closing the air-supplying electromagnetic valve502and the air-discharging electromagnetic valve503.

The control board40is a device that outputs, as an output signal to the electropneumatic regulator22, which is a pressure regulating means, a command value for the pressure of the compressed air. The control board40is provided with a differentiation circuit41, an estimation circuit42, and a coefficient multiplication circuit43.

The differentiation circuit41is a circuit for computing the derivative of the pressure in the air cylinder22detected by the pressure sensor100.

The estimation circuit42is a circuit for estimating the timing at which the cart10begins to leave the ground based on the pattern of the derivatives computed by the differentiation circuit41. The kinds of derivative patterns that are used for the estimate will be described below.

In this case, the timing at which the cart10begins to leave the ground refers to the timing at which the casters11on the cart10leave the floor surface and the total weight, which is the sum of the weight of the cart10and the weight of the cargo30loaded onto the cart10, is supported solely by the air cylinders22of the AGV20.

For example, inFIG. 6, it refers to the tail regions where the height of the cart10rises comparatively gradually before rising suddenly.

The coefficient multiplication circuit43is a circuit that computes a command value to the electropneumatic regulator22by multiplying a coefficient less than one by the pressure detected by the pressure sensor100at the timing estimated by the estimation circuit42.

When the command value computed in this way is output from the control board40to the electropneumatic regulator22, the total weight, which is the sum of the weight of the cart10and the weight of the cargo30loaded on the cart10, is not supported solely by the air cylinders22, but is also supported by the casters11on the cart10, which are grounded on the floor surface.

As a result thereof, the total weight of the cart10and the cargo30is distributed and supported not only by the two drive wheels23and the two driven wheels24on the AGV20, but also by the four casters11on the cart10. Thus, the cart10can be stably transported.

The pressure control of the electropneumatic regulator50by the control board40will be explained below.

When an input signal to the electropneumatic regulator50is supplied from the control board40in the form of a ramp function, the pressure in the lifting side (air chamber A) of the air cylinders22supporting the receiving plates25becomes greater, and the receiving plates25begin to rise. The pressure inside the air cylinders22remains approximately constant from the time at which the receiving plates25rise until they come into contact with the cart10.

Furthermore, when the receiving plates25approach close enough to contact the cart10, the proximity sensor225switches on. Thereafter, when the receiving plates25come into contact with the cart10, the pressure in the air cylinders22gradually increases, and when the pressure in the air cylinders22rises further, the cart10begins to leave the ground. Furthermore, when the cart10is in a state in which it has gradually begun to leave the ground, the derivative of the pressure in the air cylinder22becomes small. In other words, the pressure is approximately constant.

As one example, the relationship between the pressure P in an air cylinder22and the cart lift height H is shown inFIG. 6.

As shown inFIG. 6, when the input signal is supplied to the electropneumatic regulator50, the pressure P on the lifting side of the air cylinders22rises from the time t0to the time t1at which the receiving plates25begin to rise.

Furthermore, when the receiving plates25begin to rise at the time t1, the pressure P inside the air cylinders22becomes approximately constant from the time t1until the receiving plates25come into contact with the cart10.

Thereafter, when the receiving plates25approach near enough to come into contact with the cart10, the proximity sensor225switches on. When the receiving plates25come into contact with the cart10, the pressure P inside the air cylinders22gradually increases, and when the pressure P inside the air cylinders22further increases, the cart10begins to leave the ground at the time t2. Thereafter, the lift height H of the cart10gradually increases from zero, and at the timing at which the cart10begins to leave the ground, the pressure P in the air cylinders22becomes approximately constant. For this reason, at the time t3, which is some time after the cart10begins to leave the ground, the derivative of the pressure P in the air cylinders22becomes approximately zero.

When the derivative of the pressure P in the air cylinders22becomes approximately zero, even if the cart10is not lifted very much by the air cylinders22, the total weight, which is the sum of the weight of the cart10and the weight of the cargo30loaded onto the cart10, is supported solely by the air cylinders22.

Thereafter, inFIG. 6, when the air cylinders22are lifted up to the maximum stroke, the pressure P inside the air cylinders22resumes increasing and the lift height H of the cart10suddenly rises and reaches the maximum value. In this state, some of the pressure P in the air cylinders22is applied to the stoppers223.

From the above steps, the estimation circuit42estimates that the timing at which the cart10begins leaving the ground has been reached when the following conditions (1) to (3) are met:

(2) the derivative of the pressure in the air cylinders22has risen to a first prescribed value (such as 0.03 MPa/s) or higher; and

(3) the derivative of the pressure in the air cylinders22has fallen to a second prescribed value (such as 0.05 MPa/s) or lower.

However, condition (3) must be met after condition (2) has been met. In other words, for conditions (1) to (3) to be met, with the proximity sensor225switched on, the derivative of the pressure in the air cylinders22must have risen to the first prescribed value or higher, then fallen to the second prescribed value or lower. It is necessary for the derivative pattern to at least satisfy conditions (2) and (3).

When such conditions (1) to (3) are met, the coefficient multiplication circuit43computes a command value by multiplying a coefficient less than one (such as 0.9) by the pressure value at the time of condition (3) above. The computed command value is output from the control board40to the electropneumatic regulator50. Compressed air of a constant pressure is supplied from the electropneumatic regulator50to the air cylinder22, thereby allowing the cart10to be supported with an appropriate pressure without the casters11of the cart10leaving the floor surface.

In other words, when the pressure applied from the electropneumatic regulator50to the air cylinders22is 0.9 times the pressure value at the time of condition (3) above, approximately 90% of the total weight of the cart10and the cargo is supported by the air cylinders22, and the remaining approximately 10% is supported by the cart10.

An even more optimal pressure can be obtained by changing the coefficient multiplied by the pressure value depending on the pressure value obtained at the timing of condition (3) above.

For example, when the pressure measurement value (MPa)<0.3 (MPa), the coefficient is set to 0.9, and when the pressure measurement value (MPa)>0.3 (MPa), the coefficient is set to 0.7.

In the abovementioned operation, it is also possible to omit the proximity sensor225. For example, it is possible to determine the minimum pressure (for example, the pressure P in the air cylinders22at the abovementioned time t1) for supporting the receiving plates25beforehand, and to have the estimation circuit42estimate that the timing at which the cart10begins leaving the ground has been reached on the basis of only the abovementioned conditions (2) and (3) if the pressure in the air cylinders22gradually increases for a certain period of time (a few seconds) after the minimum pressure has been applied to the air cylinders22.

Furthermore, it is possible to estimate the timing at which the cart10begins leaving the ground based only on the derivative pattern.

For example, as shown inFIG. 6, there are two times at which the derivative of the pressure P in the air cylinders22becomes approximately zero.

First, between the time t1and the time t2, there is a timing at which the derivative of the pressure P in the air cylinders22becomes zero, but at this stage, the cart10has not begun to leave the ground.

Furthermore, at the time t2, the cart10begins to leave the ground, and after the time t2, there is a timing at which the pressure P in the air cylinders22becomes constant, in other words, the derivative thereof becomes zero.

Therefore, the estimation circuit42estimates that the timing at which the cart10begins leaving the ground has been reached at the timing at which the derivative of the pressure P in the air cylinders22becomes zero for the second time.

The pressure value obtained for condition (3) above allows the wheels of the cart10to always remain grounded on the floor surface and the pressure necessary for transport to be applied, regardless of whether there is an unbalanced load on the cart10. Thus, it is possible for the cart10to move, regardless of the manner in which the cargo has been loaded into the cart10, the position of the center of gravity, or the weight.

In the present embodiment, the two front and the two rear air cylinders22are respectively controlled by a single electropneumatic regulator50. However, the four air cylinders22may each be controlled by a single electropneumatic regulator50. By controlling a single air cylinder22with a single electropneumatic regulator50, it is possible to apply pressure in a complicated manner and to increase the robustness with respect to unbalanced loads.

When the drive wheels23are positioned towards the front as in the present embodiment, there is a risk that the drive wheels23will slip if the pressure in the rear air cylinders22is higher (if the load supporting the cart10is greater) than that in the front air cylinders22.

For this reason, after the pressure values in the front air cylinders22have been determined in (3) above, if the pressure in the rear air cylinders22becomes a certain value (such as 0.2 MPa) or more greater than the values in the rear cylinders22, a value obtained by adding a certain value to the pressure values in the front air cylinders22may be used as the pressure command values for the rear air cylinders22so as to keep the drive wheels23from slipping.

When each air cylinder22is lifted up by a pressure of 50% to 100% of the load from the cart10, even if it is assumed that the maximum pressure that can be applied to the air cylinders22is 0.7 MPa, the pressure becomes 0.7×100(%)/50(%)=1.4 MPa. If the coefficient applied to the pressure when the wheels of the cart10have not left the ground is set to one, as mentioned above, it is possible to transport up to twice (1.4 MPa relative to 0.7 MPa) the pressure that can be applied to the air cylinders22. Thus, the pressure of the air cylinders22can be determined even if the wheels of the cart10do not leave the ground.

The AGV according to the second embodiment of the present invention will be explained with reference toFIG. 5.

In comparison to the first embodiment, the present embodiment is characterized in that an electropneumatic regulator (not illustrated) and a pressure sensor (not illustrated) are each provided for regulating the pressure of the compressed air in each air cylinder22a,22b,22c, and22dprovided at the front, rear, left, and right of the AGV20. The remaining structures are the same as those in the aforementioned embodiment, so the same reference signs will be used and the explanations will be omitted.

The present embodiment, as illustrated inFIG. 5, is favorable for cases in which the center-of-gravity position G of the cart10including cargo is not at the center, in other words, an unbalanced load for the cart10including cargo.

When the center-of-gravity position G of the total weight of the cart10including the cargo is not at the center of the cart10, as illustrated inFIG. 5, the total weight is not evenly shared by the four air cylinders22a,22b,22c, and22d. Instead, the proportional share becomes higher as the center-of-gravity position G becomes closer. For example, in the example inFIG. 5, as the sizes of the circles indicating the air cylinders22a,22b,22c, and22dbecome larger, this indicates that a higher proportion of the load is carried.

In the case of such an unbalanced load, the closer the air cylinders22a,22b,22c, and22dare to the center-of-gravity position G, the higher the proportion of the total load that is carried, as a result of which the pressure values detected by the respective pressure sensors provided in the respective air cylinders22a,22b,22c, and22dbecome higher.

The derivative of the pressure in each air cylinder22a,22b,22c, and22ddetected by each pressure sensor is computed by a differentiation circuit (not illustrated), and based on each computed derivative pattern, the timing at which the cart10begins to leave the ground is estimated by the estimation circuit (not illustrated).

In this case, it is assumed that the cart10is kept in a horizontal state, and the estimated timing at which the cart10begins to leave the ground is the same based on any of the derivative patterns.

Then, command values are computed, in the coefficient multiplication circuit (not illustrated), by multiplying a coefficient (all the same) that is less than one by the respective pressures, in the air cylinders22a,22b,22c, and22d, detected by the pressure sensors at the same estimated timing, and these command values are respectively output from the control board (not illustrated) to the respective electropneumatic regulators.

The pressures in the air cylinders22a,22b,22c, and22dregulated by the respective electropneumatic regulators to which the command values have been respectively output in this way correspond to the proportions of the total weight that is to be carried by the respective air cylinders22a,22b,22c, and22d. In other words, the pressure becomes higher as the proportional share in the load becomes higher.

For this reason, even if the total weight of the cart10including the cargo is an unbalanced load, the weight is distributed and supported not only by the two drive wheels (not illustrated) and the two driven wheels (not illustrated) on the AGV20, but also by the four casters (not illustrated) on the cart10. Thus, the cart10can be stably transported while being kept horizontal.

In other words, the present embodiment has the advantage that, even if the cart10including the cargo is an unbalanced load, the cart10can be stably transported while being kept horizontal.

INDUSTRIAL APPLICABILITY

The present invention is widely applicable to industry as an auto guide vehicle that can stably transport a cart.

REFERENCE SIGNS LIST