Multiple hoist synchronization apparatus and method

1. A material handling equipment synchronization apparatus for synchronizing positions of a first material handling device and a second material handling device, the first material handling device including a first driven motor connected to a first pulse encoder adapted to generate a first pulse signal, the second material handling device including a second driven motor connected to a second pulse encoder adapted to generate a second pulse signal, the apparatus comprising:

a master inverter adapted to monitor the first pulse signal and control the first driven motor; and

a slave inverter adapted to monitor the first pulse signal and the second pulse signal and control the second driven motor, the slave inverter further adapted to derive a position error from the first pulse signal and second pulse signal and adjust the second driven motor to compensate for the position errors.

2. The material handling equipment synchronization apparatus of claim 1 further adapted for synchronizing positions of the first material handling device and a second material handling device by means independent of timing control,

wherein, the slave inverter is further adapted to control the second driven slave motor based on the first pulse signal and the second pulse signal

wherein the controlling is done independently from a timing control.

3. The apparatus of claim 1 , wherein, the slave inverter is adapted to generate an output signal for controlling the second driven motor, and

wherein, the slave inverter is further adapted to compensate for the position errors by

adjusting the output signal to change the motor position to minimize the position error.

4. The apparatus of claim 1 , wherein alignment of the material handling devices is maintained by minimizing position error while both drives are running.

5. The apparatus of claim 1 , wherein the slave inverter possesses an automatic resynchronization feature to resynchronize the position of the material handling devices after either of the drives has been operated independently by reducing position error accumulated during the independent operation of the drives.

6. The apparatus of claim 5 , wherein selection of the automatic resynchronization feature is controlled by a parameter on the slave drive.

7. The apparatus of claim 1 , wherein both material handling devices have an associated position limit, and the position error is cleared when both material handling devices are moved to the position limit.

8. The apparatus of claim 1 , wherein the slave inverter further comprises an error clearing input for receiving an error clearing signal, the slave inverter adapted to clear the position error upon receipt of the error clearing signal.

9. The apparatus of claim 1 , wherein the slave inverter further comprises an electronic gearing control adapted to operate the second driven motor at a speed ratio of the first driven motor.

10. A hoist synchronization software method for operating a slave controller adapted to control a slave motor attached to a slave encoder in coordination with a master controller adapted to control a master motor attached to a master encoder which provides a pulse reference to the slave controller, the method comprising:

monitoring pulse feedback from both the master encoder and the slave encoder;

calculating a position error from the pulse feedback;

compensating for any position error by adjusting the slave motor output speed.

11. The method of claim 10 , wherein the slave controller comprises a microprocessor controlled inverter, and wherein, the master controller follows a master controller trajectory, the method further including the steps of:

receiving the master controller trajectory at the inverter; and

wherein the compensation step includes controlling the slave motor to follow the master drive trajectory.

12. The method of claim 10 , the method further comprising the steps of:

generating a master encoder signal indicative of the operation of the master motor;

calculating the speed of the master motor from the master encoder signal;

calculating an adjustment ratio;

adjusting the calculated speed in accordance with the adjustment ratio to generate an adjusted calculated speed;

modifying the calculated for proportional gain;

modifying the calculated for integral gain;

selecting from a standard drive reference and frequency reference;

regulating the speed of the slave motor in accordance with the selected signal; and

generating a slave encoder signal indicative of the operation of the slave motor.

13. The method of claim 10 , further comprising:

storing position error generated when either the master motor or the slave motor is run independently; and

correcting for the position error when both the master and the slave motor are commanded to operate at a later time.