Steer control system for material handling vehicles

An apparatus for adjusting a steer center position for an AGV, the apparatus comprising:

• a central processing unit;
• a distance from wire detector electrically coupled to the central processing unit;
• a drive traction feedback encoder electrically coupled to the central processing unit;
• a steer feedback encoder electrically coupled to the central processing unit;
• a read only memory component electrically coupled to the central processing unit, the read only memory component storing data correlating distance from wire to steer center position adjust data;
• and
• a nonvolatile random access memory component electrically coupled to the central processing unit, the nonvolatile random access memory component storing a steer center position value, wherein the central processing unit is programmed to:
• retrieve the steer center position value from the nonvolatile random access memory;
• monitor an output signal from the drive traction encoder to determine an instantaneous travel position of the AGV and a total travel distance;
• monitor an output signal from the distance from wire detector to determine an instantaneous distance from wire value at a plurality of travel positions;
• monitor an output signal from the steer feedback encoder:
• calculate an average distance from wire over the total travel distance;
• retrieve a steer center position adjust value correlated to the average distance from wire from the read only memory;
• and
• adjust the output signal from the steer feedback encoder by the steer center position adjust value.

An automatic guided vehicle (AGV) of the type that follows a wire, the AGV comprising:

• a steering assembly including a steer motor and a steer feedback encoder;
• a traction assembly including a drive motor, a drive motor encoder, and a drive tire, the traction assembly being coupled to a tractor chassis of the AGV to provide a motive force to the AGV;
• a control system, electrically coupled to the steer motor, the steer feedback encoder, the drive motor, and the drive motor encoder;
• and
• a distance from wire detector electrically coupled to the control system, wherein the control system is programmed to:
• receive a feedback position signal from the drive motor encoder, a distance from wire signal from the distance from wire detector, and steer encoder feedback data from the steer feedback encoder;
• calculate an average distance from wire over a predetermined distance;
• calculate an adjustment of a steer center position based on the average distance from wire;
• calculate an adjusted steer encoder feedback as the sum of the steer feedback encoder data and the adjustment of the steer center position.
• calculate a command to the steer motor based on feedback from the distance from wire detection and the adjusted steer encoder feedback.

A method for tuning a steer center position of an automatic guided vehicle of the type which travels along a guide wire, the method comprising the following steps:

• slewing a motor to trip a home switch;
• storing an initial steer center position correlating to the position at which the home switch is tripped;
• monitoring a distance traveled by the automatic guided vehicle;
• establishing a plurality of predetermined travel increments in a predetermined total distance;
• determining a distance from wire value for the automatic guided vehicle at each predetermined travel increment;
• calculating an average distance from wire over the number of predetermined travel increments in the predetermined total travel distance;
• and
• adjusting the initial steer center position to account for differences between the initial steer center position and the steer center position, wherein the adjustment is a function of the average distance from wire.