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Cross Coupled Gantry w/ Single Encoder and Hall


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Would there be any problems using the Power Pmac X coupled gantry servo algorithm with a single encoder and hall sensor for both motors, assuming the gantry is sufficiently stiff?


The single encoder is used for commutation and position/velocity feedback on both motors and the hall sensor to establish phasing upon power up. Both motors are the same size linear motor.


In theory it seems possible, but I want to make sure that I'm not missing something here.






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The cross coupled gantry is only useful if each motor has its encoder and using the difference between the data from each encoder the cross coupled gantry algorithm will determine the correction in force/DAC output to each motor. Having one encoder is not sufficient for cross coupled since there is no secondary encoder, meaning there is no difference which results in zero cross coupled gantry output.


However, what you can do is to use Power PMAC's leader/follower scheme to accomplish this:


- Setup each motor as if they are independent.

- Set the Motor[x].ServoCtrl for follower motor to 8.

- Set Motor[x].CmdMotor for the follower motor x to motor number of leader motor.

- Define the leader motor with proper axis definition statement or kinematic routine in a coordinate system.

- Assign the follower motor to 0 in the same coordinate system where leader is defined. (a.e. #x->0)


Now the motors are in leader/follower mode.



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