Method and system for a lift device control system

1. A scissors lift vehicle control system comprising:

a main computer comprising one or more processors and one or more memory devices communicatively coupled to said one or more processors;

a steer controller configured to receive commands from said main computer to control a plurality of independently steerable wheel assemblies, each wheel assembly comprising a steer angle sensor, a steer angle actuator, and a drive motor;

a scissors lift controller configured to control a hydraulic piston assembly comprising a hydraulic fluid reservoir internal to a piston rod assembly;

an interlock system comprising:

a tilt sensor configured to determine an angle of incline the scissors lift vehicle; and

a pothole proximity switch;

a variable-speed steer actuator configured to rotate a wheel assembly about a steer axis of rotation at a selectable rate;

a wheel comprising a respective drive axis of rotation; and

a variable-speed drive actuator configured to rotate said wheel about said respective drive axis of rotation at a selectable rate.

2. The scissors lift vehicle control system of claim 1 , wherein the plurality of independently steerable wheel assemblies includes a wheel assembly designated as a master wheel assembly and wherein said one or more processors are configured to:

receive a steer input from a user input device;

generate a steer actuator speed command signal based on the steer input; and

transmit the steer actuator speed command signal to the variable-speed steer actuator of the designated master wheel assembly.

3. The scissors lift vehicle control system of claim 1 , wherein said one or more processors are configured to receive a steer mode selection including a two-wheel steer mode, a four-wheel steer mode, and a crab steer mode.

4. The scissors lift vehicle control system of claim 1 , wherein said interlock system is configured to prevent operation of said scissors lift controller and said variable-speed drive actuator concurrently.

5. The scissors lift vehicle control system of claim 1 , wherein said one or more processors are further configured to prevent raising a scissors stack assembly when a tilt detected by said tilt sensor exceeds a predetermined amount.

6. The scissors lift vehicle control system of claim 1 , further comprising a single-axis joystick control configured to generate steering signals based on a manual input by a user.

7. The scissors lift vehicle control system of claim 1 , further comprising a dual-axis joystick control configured to generate left and right steering signals and forward and reverse drive signals based on a manual input by a user.

8. The scissors lift vehicle control system of claim 1 , wherein said one or more processors are configured to receive a steer angle input signal representative of an angle determined by a rotary sensor coupled to each of a plurality of independently steerable wheels.

9. The scissors lift vehicle control system of claim 1 , wherein said one or more processors are configured to:

receive a steer command from a user input device;

determine a first steering speed command for a first wheel assembly based on the steer command, the first wheel assembly independent of all other wheel assemblies; and

determine a target steering angle for a second wheel assembly, the determined target steering angle based on a current steering angle of the first wheel assembly.

10. The scissors lift vehicle control system of claim 9 , wherein said one or more processors are further configured to:

determine a second steering speed command for the second wheel assembly based on a difference between a current steering angle of the second wheel assembly and the determined target steering angle; and

alter a course of travel of the scissors lift vehicle using the first and second steering speed commands.

11. A method of controlling a scissors lift vehicle, the scissors lift vehicle including a plurality of independently steerable wheel assemblies, the method comprising:

receiving a steer command from a user input device;

determining a first steering speed command for a first wheel assembly of the plurality of wheel assemblies based on the steer command, the first wheel assembly independent of all other wheel assemblies with respect to a steering angle, a speed of rotation about a steer axis, and a drive speed;

determining a target steering angle for a second wheel assembly, the target steering angle based on a current steering angle of the first wheel assembly;

rotating the first wheel assembly about a first wheel assembly steer axis at a first steering speed to a first wheel assembly target steering angle based on the received steer command; and

rotating the second wheel assembly about a second wheel assembly steer axis at a second steering speed to the determined target steering angle, the second steering speed not intentionally constrained.

12. The method of claim 11 , further comprising:

determining a second steering speed command for the second wheel assembly based on a difference between a current steering angle of the second wheel assembly and the determined target steering angle; and

altering a course of travel of the scissors lift vehicle using the first and second steering speed commands.

13. The method of claim 11 , further comprising receiving a steer angle input signal representative of an angle determined by a rotary sensor coupled to each of a plurality of independently steerable wheels.

14. A scissors lift vehicle comprising:

a main computer comprising one or more processors and one or more memory devices communicatively coupled to said one or more processors;

a steer controller configured to receive commands from said main computer to control a plurality of independently steerable wheel assemblies, each wheel assembly comprising a steer angle sensor, a steer angle actuator, and a drive motor;

a scissors lift controller configured to control a hydraulic piston assembly comprising a hydraulic fluid reservoir internal to a piston rod assembly;

an interlock system comprising:

a tilt sensor configured to determine an angle of incline the scissors lift vehicle; and

a pothole proximity switch;

a variable-speed steer actuator configured to rotate a wheel assembly about a steer axis of rotation at a selectable rate;

a wheel comprising a respective drive axis of rotation; and

a variable-speed drive actuator configured to rotate said wheel about said respective drive axis of rotation at a selectable rate.

15. The scissors lift vehicle of claim 14 , wherein the plurality of independently steerable wheel assemblies includes a wheel assembly designated as a master wheel assembly and wherein said one or more processors are configured to:

receive a steer input from a user input device;

generate a steer actuator speed command signal based on the steer input; and

transmit the steer actuator speed command signal to the variable-speed steer actuator of the designated master wheel assembly.

16. The scissors lift vehicle of claim 14 , wherein said one or more processors are configured to receive a steer mode selection including a two-wheel steer mode, a four-wheel steer mode, and a crab steer mode.

17. The scissors lift vehicle of claim 14 , wherein said interlock system is configured to prevent operation of said scissors lift controller and said variable-speed drive actuator concurrently.

18. The scissors lift vehicle of claim 14 , wherein said one or more processors are further configured to prevent raising a scissors stack assembly when a tilt detected by said tilt sensor exceeds a predetermined amount.

19. The scissors lift vehicle of claim 14 , wherein said one or more processors are configured to:

receive a steer command from a user input device;

determine a first steering speed command for a first wheel assembly based on the steer command, the first wheel assembly independent of all other wheel assemblies; and

determine a target steering angle for a second wheel assembly, the determined target steering angle based on a current steering angle of the first wheel assembly.

20. The scissors lift vehicle of claim 19 , wherein said one or more processors are further configured to:

determine a second steering speed command for the second wheel assembly based on a difference between a current steering angle of the second wheel assembly and the determined target steering angle; and

alter a course of travel of the scissors lift vehicle using the first and second steering speed commands.