Master-servant structured synchronization scheme and its application in multi-pole table-lift

For the purpose of synchronization of three independent DC motors which were used to drive the supporting poles of a table-lift, a “master-servant” structured control scheme is introduced. By taking the master pole's output as reference signal and the servant pole's output as feedback signal, servant poles become the followers of the master pole. Hall sensors are employed to transmit the rotations of the motors as well as the upward or downward speeds of the supporting poles into pulse signals. These pulse signals are counted by a micro-processor and then processed numerically. Using a special counting method, the difference between the outputs of the master and servant poles creates an error signal. This way, the lengths of the registers for pulse counting are limited to 8 bits, no matter how many pulses reach the micro-processor. Two numerical arithmetic schemes for the pulse width modulation are used for even more precise control. Experimental results are also presented.