HK1195930A - Vehicle with solicited carriage descent - Google Patents

Description

Vehicle with requested carriage descent

Cross Reference to Related Applications

Not applicable.

Statement regarding federally sponsored research

Not applicable.

Background

The material handling truck includes a carriage that is movable up and down along the mast and a hydraulic cylinder for moving the carriage. The hydraulic pump pumps hydraulic fluid into the hydraulic cylinder to propel the piston within the hydraulic cylinder and lift the carriage along the mast. When the carriage is lowered, hydraulic fluid is allowed to drain out of the hydraulic cylinder. The hydraulic cylinder includes a flow restriction valve that only allows hydraulic fluid to flow into and out of the hydraulic cylinder up to a flow limit. The flow restriction valve ensures that the lowering speed of the carriage is limited when an unsolicited lowering of the carriage occurs. Unfortunately, the flow restriction valve also limits the rate of descent of the carriage when the operator requests that the carriage be raised or lowered. In a warehouse storage environment, the production rate of material handling vehicles is based in part on how many pallets can be raised or lowered from a rack per hour. Thus, limiting the speed of the carriage requested to be lowered limits the productivity of the material handling vehicle.

Therefore, there is a need for a system that limits only the carriage descent speed when an unsolicited carriage is descending.

Disclosure of Invention

The present invention provides a vehicle including a frame, a vertical mast coupled to the frame, and a carriage movably mounted to the mast for raising and lowering along the mast. The vehicle also includes one or more hydraulic cylinders that move the carriage along the mast, a hydraulic pump that pumps hydraulic fluid into the hydraulic cylinders, and a flow valve that controls the flow of hydraulic fluid between the hydraulic pump and the hydraulic cylinders. The vehicle also includes a sensor that senses an actual descent speed of the carriage and a controller that controls the flow valve to allow the carriage to descend at a requested descent speed. The controller controls the flow valve to limit descent of the carriage to an unsolicited descent speed limit if a difference between the actual descent speed and the demanded descent speed exceeds a threshold.

It is a general object of the present invention to control the rate of descent of a carriage along a mast mounted to a vehicle frame. This object is achieved by determining a requested lowering speed of the carriage, sensing an actual lowering speed of the carriage, and comparing the requested lowering speed and the actual lowering speed to determine a difference. The object is also achieved by comparing the difference with a threshold value and limiting the actual descent speed to an unclaimed descent speed limit if the difference is greater than the threshold value.

The foregoing and other objects and advantages of the invention will be apparent from the following detailed description. In the description, reference is made to the accompanying drawings that show preferred embodiments of the invention.

Drawings

FIG. 1 is a rear perspective view of a vehicle according to one embodiment of the present invention.

FIG. 2 is another rear perspective view of the vehicle of FIG. 1.

FIG. 3 is a communication flow diagram of components of the vehicle of FIG. 1.

FIG. 4 is a partial view of a hydraulic system for use with the vehicle of FIG. 1.

FIG. 5 is a flow chart of example initialization and calibration operations of components of the vehicle of FIG. 1.

Detailed Description

Conventional material handling vehicles limit the maximum lowering speed at which the carriage can move vertically along the mast to about 118 feet per minute. Advantageously, the vehicle described herein in connection with the present invention may achieve a descent speed greater than a standard maximum descent speed while limiting the descent speed to an unsolicited descent speed limit during an unsolicited carriage descent. In one embodiment, a vehicle controller controlling the carriage distinguishes a requested carriage descent from an unsolicited carriage descent by comparing the actual speed of the carriage sensed by the sensor to the descent speed requested by the operator, as described further below.

Referring to fig. 1 and 2, the material handling vehicle 10 includes a frame 12, a mast 14 coupled to the frame 12, and a carriage 16 movable along the mast 14. As shown in fig. 3 and 4, the hydraulic system 18 is mounted on the vehicle 10 and raises and lowers the carriage 16 along the mast 14 in response to input from an operator. For example, fig. 1 shows the carriage 16 in a lowered position, while fig. 2 shows the carriage 16 in a raised position. The hydraulic system 18 is requested by a vehicle controller 20, which receives operator input as well as other input from a sensor 22 that senses the vertical raising or lowering speed of the carriage 16. In the embodiment disclosed herein, the operator controls the hydraulic system 18 via an operator input control 24 that is in communication with the vehicle controller 20, thereby controlling the raising and lowering of the carriage 16 along the mast 14. Exemplary vehicles that can incorporate the present invention include Reach-Fork or Swing-Reach trucks, manufactured by Redmond, Inc. of Green, N.Y.

The hydraulic system 18 of the vehicle 10 includes one or more hydraulic cylinders 30, as shown in FIG. 4, a hydraulic pump 32, a pump motor controller 34, as shown in FIG. 3, and one or more flow valves 36. The hydraulic pump 32 is requested (e.g., communicated to and requested by the vehicle controller 20) by a pump motor controller 34 to deliver hydraulic fluid into and out of the hydraulic cylinder 30. More specifically, hydraulic fluid flows through the hydraulic pump 32 into the hydraulic cylinder 30 (i.e., causing the piston 37 to move upward within the hydraulic cylinder 30) to raise the carriage 16 and back out of the hydraulic cylinder 32 through the hydraulic pump 32 (i.e., causing the piston 37 to move downward) to control the carriage's descent and provide regenerative energy to the vehicle 10.

The pump motor controller 34 may operate the hydraulic cylinders 32 at different speeds to control the amount of fluid flowing into the hydraulic cylinders 30, which in turn controls the speed of raising or lowering the carriage 16. For example, assuming that the diameter of each hydraulic cylinder 30 is fixed and the hydraulic pump 32 has a fixed fluid discharge per revolution, the speed of movement of the carriage 16 is always a function of the pump speed (e.g., measured in revolutions per minute, or RPM, of the motor of the pump 32) and the direction of rotation of the pump 32. Thus, under appropriate operating conditions, the following relationship is suitable for converting the carrier speed to pump speed: carriage speed = K × RPM, where RPM <0 on descent, RPM >0 on ascent, and K is a constant.

In addition to the pump motor controller 34, the flow valve 36 also controls the amount of fluid flowing to the hydraulic cylinder 30 and, therefore, also the speed of ascent or descent of the carriage 16. Flow valves 36 are positioned in the fluid path between hydraulic pump 32 and hydraulic cylinder 30 to selectively allow or restrict flow between hydraulic pump 32 and hydraulic cylinder 30. Each flow valve 36 communicates with the vehicle controller 20 such that the operating state of the flow valve 36 is dependent upon input from the vehicle controller 20. For example, if power is received from the vehicle controller 20, the flow valve 36 remains in a fully open state (i.e., a bypass state) to allow unrestricted fluid flow between the hydraulic pump 32 and the hydraulic cylinder 30. If no power is received from the vehicle controller 20, the flow valve 36 is partially closed to act as a conventional flow restriction valve (i.e., in a throttled or flow-restricted state) and prevent fluid from flowing beyond a maximum flow value, thereby preventing the descent speed from exceeding an unsolicited descent speed limit (e.g., approximately 118 feet per minute).

Thus, in the throttled state, the flow valve 36 restricts fluid flow and must receive electrical power by the vehicle controller 20 in order to change the operating state of the flow valve 36 to the bypass state. To accomplish this, each flow valve 36 includes a solenoid 38, as shown in FIG. 3. When the vehicle controller 20 provides power to the solenoid 38, the solenoid 38 maintains the flow valve 36 open in the bypass state. Thus, when unrestricted flow is permitted, the solenoid 38 receives power from the vehicle controller 20 and bypasses normal mechanical operation of the flow valve, which limits flow above a flow value corresponding to an unsolicited descent speed limit of the carriage. Without power, the solenoid 38 will not hold the flow valve 36 open and the flow will be limited to a flow value corresponding to the drop speed limit for which the carriage is not requested. In some embodiments, solenoid 38 and flow valve 36 may be integrated with hydraulic cylinder 30 or mounted to hydraulic cylinder 30. Further, other embodiments of the invention may include other combinations of mechanical and/or electrical components to repeat the above-described functions of the flow restriction valve, which may be bypassed by the application of electrical power.

During normal vehicle operation when the operator requests carriage lowering and raising, the flow valve 36 is in a bypass state and the vehicle controller 20 provides power to the solenoid 38 to allow unrestricted flow into and out of the hydraulic cylinder 30. Upon the occurrence of an unsolicited descent, the vehicle controller 20 cuts off power to the solenoid 38 to restrict flow. To determine the unsolicited descent, the actual carriage speed is detected by sensor 22 shown in FIG. 3. Preferably, the sensor 22 is mounted to the carriage 16 and includes a solid state micro-electromechanical (MEM) accelerometer 26. The MEM accelerometer allows the sensor 22 to measure the vertical velocity of the carriage 16 (i.e., along its respective Z axis, as shown in fig. 1) regardless of the motion of the vehicle 10 along its respective x and y axes or the tilt of the mast 14 while the carriage 16 is being raised or lowered. Preferably, the sensor 22 includes an electrical connection to the negative power supply line of the vehicle, as well as an electrical connection to the vehicle controller 20. Through the electrical connection of the vehicle controller 20, the sensor 22 receives electrical power and transmits a carriage speed signal. The sensor 22 also includes a microcontroller 28 for interpreting accelerometer measurements and communicating with the vehicle controller 20.

In some embodiments, other velocity sensing devices may be used in place of MEM accelerometer 26. In one example, a magnetic sensor may be used to detect the passage of a hole or protrusion along the mast 14 over a period of time to obtain the descent speed. In another example, optical, microwave, or ultrasonic sensors may measure the distance from the floor to the carriage 16, and the distance measurements may be differentiated to obtain the descent speed.

As described above, the vehicle controller 20 is mounted on the frame 12, and controls the flow valve 36 by supplying power to the solenoid 38 or cutting off power to the solenoid 38, as shown in fig. 2. The vehicle controller 20 also performs other functions associated with the vehicle 10, including receiving operator input to raise or lower the carriage 16 and controlling the raising or lowering of the carriage 16 in accordance with the operator input. More specifically, with respect to carriage descent, the vehicle controller 20 receives a requested descent speed input from the operator input control 24 and determines the hydraulic pump rotational speed necessary to achieve the requested carriage descent speed (e.g., using the above-described conversion equation). The vehicle controller 20 then provides a speed control signal to the pump motor controller 34 to operate the hydraulic pump 32 at the determined pump motor speed. The vehicle controller 20 also receives feedback from the pump motor controller 34 indicating the actual rotational speed of the pump 32. Using the actual rotational speed of the pump 32, the vehicle controller 20 then determines the calculated descent speed (e.g., by applying a conversion equation). Further, in some vehicles, carrier descent is only subject to operator-controlled throttle actuation, as opposed to the pump 32 operating in the opposite (i.e., negative RPM) direction. In such an example, the desired rate of descent is determined directly by an operator input control, such as an operator input control position or control signal generated by the operator input control, or by a control signal to the throttle valve generated by a controller that receives the control signal from the operator input control.

The vehicle controller 20 also communicates with a sensor 22 that measures the actual speed of movement ("CSPEED") of the carriage 16. The vehicle controller 20 receives the CSPEED signal from the sensor 22 and compares it to the desired descent speed as described above. The vehicle controller 20 uses the requested descent speed or the calculated descent speed received by the operator input control 24 as the requested descent speed for the comparison. The vehicle controller 20 then calculates the difference between the actual descent speed and the requested descent speed, "DELTA," e.g., feet per minute, (e.g., DELTA-CSPEED-requested descent speed). A negative DELTA value indicates that the carriage 16 is dropping slower than indicated by the pump speed. Likewise, a positive DELTA value indicates that the carriage descent speed is higher than the pump speed indication. Since the requested carriage speed is based on operator input, any difference between the requested carriage speed and the actual carriage speed may indicate an unsolicited carriage movement.

As described above, the flow valve 36 throttles fluid flow unless the vehicle controller 20 transmits power to the solenoid 38 (i.e., energizes the solenoid 38) to keep the flow valve 36 open. When the absolute value of DELTA exceeds the threshold, the vehicle controller 20 determines that carriage movement is not requested and cuts power to the solenoid 38 (i.e., de-energizes the solenoid 38), placing the control valve in a throttled state to limit the rate of descent of the carriage 16 to the unsolicited rate of descent limit.

If the absolute value of DELTA remains below the threshold, the vehicle controller 20 determines that carriage movement is requested and continues to power the solenoid 38, and thus, allows the descent speed to be above the unsolicited descent speed limit. This allows the carriage descent speed to be above the unsolicited descent speed limit only if carriage movement is requested by the operator. Advantageously, if the vehicle controller 20 itself experiences a fault, the sensor 22 experiences a fault, or if communication between the solenoid 38 and the vehicle controller 20 or between the sensor 22 and the vehicle controller 20 is somehow impeded, the solenoid 38 will cease receiving power and will not be able to maintain the flow valve 36 in the bypass state, thus limiting the carriage descent speed to an unsolicited descent speed limit.

In addition to transmitting the CSPEED signal, as described above, the sensors 22 and the vehicle controller 20 also communicate to perform one or more calibration procedures to maintain the accuracy of the sensors 22 over time and under various operating conditions. For example, FIG. 5 illustrates the steps performed by the sensor microcontroller 28 (processing blocks 40-50) and the vehicle controller 20 (processing blocks 52-64) to calibrate the zero acceleration signal (AZERO) and the zero pump speed signal (ZRPM) in one embodiment, which may remove drift in the measurements that typically occurs due to temperature and/or long time error accumulation. Communication between the operation of the sensor microcontroller 28 and the operation of the vehicle controller 20 is shown in dashed lines in fig. 5.

As shown in fig. 5, the sensor microcontroller 28 and the vehicle controller 20 perform an initialization function when power is supplied to the vehicle 10 (i.e., ON KEY), and periodically perform a calibration function to eliminate errors when the carriage 16 is not moving. These operations both improve the accuracy of the sensor speed signal and allow for fail-safe operation between the two components (e.g., so that the unsolicited movement of the carriage 16 is properly detected and results in the descent speed of the carriage being limited to an unsolicited descent speed limit). Referring to FIG. 5, at KEYON (processing block 40), the sensor microcontroller 28 determines the current output of the accelerometer 26 and records this value as a zero acceleration value, AZERO. Further, at KEY ON (processing block 52), the vehicle controller 20 ensures that power is not provided to the solenoid 38.

With further reference to the functionality of the sensor microcontroller 28 of fig. 5, immediately after KEY ON, the sensor microcontroller 28 updates its clock (processing block 42) and then determines whether a zero pump speed signal, ZRPM, has been received by the vehicle controller 20, indicating that the carriage 16 is not moving (processing block 44). For example, the ZRPM signal may be generated when the hydraulic pump 32 has not rotated (i.e., pump revolutions per minute equals zero) for at least about 100 milliseconds. If the ZRPM signal has been received, the sensor microcontroller 28 resets the carrier speed signal CSPEED to zero (processing block 46) and sends an updated speed signal CSPEED to the vehicle controller 20 (processing block 50). If the ZRPM signal has not been received, the sensor microcontroller 28 updates the CSPEED by adding the currently stored CSPEED value to the product of the acceleration signal from the MEM accelerometer and the CLOCK duration from the CLOCK (i.e., CSPEED = CSPEED + A × CLOCK) (processing block 48), and sends the updated CSPEED signal to the vehicle controller 20 (processing block 50). After sending the updated CSPEED signal to the vehicle controller 20, the sensor microcontroller 28 repeats process blocks 42-50.

Once the zero acceleration signal is calibrated at least once, immediately after KEY ON in the embodiment shown in FIG. 5, the vehicle controller 20 determines whether the hydraulic pump speed has reached at least 100 milliseconds at zero RPM (processing block 54). If the RPM of the pump 32 is zero for at least 100 milliseconds, the vehicle controller 20 sends a ZRPM signal to the sensor microcontroller 28 (processing block 56). If the RPM of the pump 32 is not zero for at least 100 milliseconds, the vehicle controller 20 calculates the requested carrier speed (i.e., carrier speed K RPM) using the pump RPM received from the motor controller 34 and the above conversion equation (i.e., carrier speed = K RPM), and then calculates the difference, DELTA, between the calculated speed and the final CSPEED value received from the sensor microcontroller 28 (process block 58). The vehicle controller 20 then determines whether the absolute value of DELTA is greater than or less than a threshold (process block 60). If less than the threshold, the vehicle controller 20 considers carrier movement to be requested and powers the solenoid 38 to allow unrestricted flow through the flow valve 36 (process block 62). If greater than the threshold, the vehicle controller 20 considers the carriage movement to be unsolicited and turns off power to the solenoid 38 so that flow through the flow valve 36 is prevented, thereby limiting the carriage descent speed to an unsolicited descent speed limit (process block 64). The vehicle controller 20 then repeats process blocks 54-64.

In some embodiments, the processing of the vehicle controller 20 (i.e., processing blocks 54-64) and the sensor microcontroller 28 (i.e., processing blocks 42-50) is repeated fifty or more times per second. Further, in one embodiment, the sensor microcontroller processing shown in FIG. 5 is the only function performed by the sensor microcontroller 28.

As described above, communication between the sensor microcontroller 28 and the vehicle controller 20 is transmitted in both directions. The bidirectional communication is realized by a single communication line through Power Line Communication (PLC) or other similar methods. In one embodiment, the vehicle controller 20 provides a fixed 5 volt power supply through a 100 ohm resistor or a 500 ohm resistor through an electrical connection between the vehicle controller 20 and the sensor microcontroller 28. For example, vehicle controller 20 typically applies 5 volts across a 100 ohm resistor and sensor microcontroller 28 sinks with even a current from about 4 milliamps (mA) to about 20 milliamps (mA) to represent the CSPEED value, as well as the signals to vehicle controller 20 that sensor 22 is still connected and operating. Also, the vehicle controller 20 switches from a resistance of 100 ohms to a resistance of 500 ohms to indicate that the pump 32 is not rotating (i.e., transmitting the ZRPM signal).

It is an object of the present invention to maintain all of the desirable characteristics of an unsolicited descent speed limit when an unsolicited operation occurs and to allow the speed to be reduced beyond the unsolicited descent speed limit during a requested operation. Achieving a faster descent speed can increase productivity and thus save labor costs. Further, when using the hydraulic pump 32 as a generator, the faster descent speed may also contribute to energy regeneration of the vehicle 10. By continually determining whether the carriage 16 is in a requested descent or an unsolicited descent, the present invention provides a reliable method of returning the unsolicited carriage descent to the industry standard descent speed limit. This unsolicited carriage drop can be accurately and timely detected by constant calibration between the sensor 22 and the vehicle controller 20.

Furthermore, the system and method of the present invention can be used for different vehicle designs. For example, the vehicle 10 without a reproducible descent may not include the hydraulic pump 32, which rotates backward during the descent of the carriage. Such a vehicle 10 optionally includes additional pressure sensors and/or flow measurement devices (not shown) to determine a desired carrier velocity value for comparison with sensor measurements. Further, such a vehicle 10 uses vacuum or pressure assistance between a hydraulic pump 32 and a double acting hydraulic cylinder 30 to control carriage descent. Other design changes according to the present invention include a large diameter pipe between hydraulic pump 32 and hydraulic cylinder 30 to allow a higher flow rate back through hydraulic pump 32.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined by the appended claims.

Claims (20)

1. A vehicle, comprising:

a frame;

a vertical mast coupled to the frame;

a carriage movably mounted to the mast for raising and lowering along the mast;

at least one hydraulic cylinder for moving said carriage along said mast;

a hydraulic pump that pumps hydraulic fluid into the at least one hydraulic cylinder;

a flow valve controlling a flow of hydraulic fluid between the hydraulic pump and the at least one hydraulic cylinder;

a sensor that senses an actual lowering speed of the carriage; and

a controller controlling the flow valve to allow the carriage to descend at a requested descent speed, the controller controlling the flow valve to limit descent of the carriage to an unsolicited descent speed limit if a difference between the actual descent speed and the requested descent speed exceeds a threshold.

2. The vehicle of claim 1, characterized in that if the difference between the actual descent speed and the requested descent speed is less than the threshold value, the controller controls the flow valve to allow the descent of the carrier to be greater than the unsolicited descent speed limit.

3. The vehicle of claim 2, characterized in that the flow valve limits the flow of hydraulic fluid to limit the descent of the carriage to the unsolicited descent speed limit, and the flow valve allows unrestricted flow of hydraulic fluid to allow the descent of the carriage above the unsolicited descent speed limit.

4. The vehicle of claim 3, characterized in that the flow valve is normally in a flow restricting operating state to restrict the flow of hydraulic fluid, wherein the controller opens the flow valve to allow unrestricted flow of hydraulic fluid.

5. The vehicle of claim 4, comprising a solenoid coupled to the flow valve and requested by the controller, wherein the flow valve is open when the solenoid is energized by the controller and the flow valve is in the flow-restricting operating state when the solenoid is de-energized.

6. The vehicle of claim 1, wherein the controller determines the requested descent speed by measuring a rotational speed of the hydraulic pump.

7. The vehicle of claim 1, characterized in that the sensor is a micro-electromechanical accelerometer.

8. The vehicle of claim 1, characterized in that the controller is in communication with the sensor and receives the actual descent speed from the sensor.

9. The vehicle of claim 8, wherein the sensor comprises a sensor microcontroller in communication with the controller, wherein the actual descent speed is zeroed by the sensor microcontroller when the controller determines that the rotational speed of the hydraulic pump is equal to zero, the sensor microcontroller and the controller periodically executing a calibration routine.

10. The vehicle of claim 9, characterized in that the sensor microcontroller executes an initialization routine when power is initially received by zeroing the actual descent speed.

11. The vehicle of claim 1, wherein the unsolicited descent speed limit is approximately 118 feet per minute.

12. The vehicle of claim 1, wherein the controller determines the requested descent speed directly from one of an operator control input signal, an operator control position, and a throttle control signal.

13. A method of controlling the rate of descent of a carriage along a mast mounted to a vehicle frame, the method comprising:

determining a required lowering speed of the carriage directly from a control signal;

sensing an actual lowering speed of the carriage;

comparing the requested descent speed and the actual descent speed to determine a difference;

comparing the difference to a threshold; and

limiting the actual descent speed to an unsolicited descent speed limit if the difference is greater than the threshold.

14. The method of claim 13, comprising sensing the actual rate of descent of the carriage using a sensor comprising a micro-electromechanical accelerometer.

15. The method of claim 14, comprising calibrating the sensor while the carriage is stationary to ensure that sensing the actual descent speed is accurate while the carriage is moving.

16. The method of claim 13, wherein the method comprises: if the difference is less than the threshold, the actual descent speed is allowed to reach above the unrequested descent speed limit.

17. The method of claim 13, comprising limiting the actual descent speed by limiting a flow of hydraulic fluid through a hydraulic system that controls movement of the carriage.

18. The method of claim 17, comprising restricting the flow of hydraulic fluid using a flow valve of a requested solenoid.

19. The method of claim 13, comprising determining the requested rate of descent from one of an operator control input signal and a throttle control signal.

20. The method of claim 13, wherein the unsolicited descent speed limit is approximately 118 feet per minute.