In our last posting we raised some questions about how the “position make up” made up for the steps that were removed.
Our last few postings talked about the “torque mode” operational theory that we added to our “Hybrid” drive. Prior to that we added “variable current mode” and “position makeup”
In our last posting we discussed how we made our “Hybrid Drive” act like a torque motor.
One issue that you do have be aware of is the fact that at some point in the stepper’s speed-torque curve the torque is going to begin to fall off as a function of speed just as it did with the AC torque motors.
In our last posting we discussed an application where we used our “Hybrid” drive in the “Torque Mode” to apply tension to a web.And we asked how does the “Hybrid” drive know what speed to operate at when the web velocity changes? It’s looking at its own rotor encoder information. If the encoder begins to move, then the control generates an appropriate number of steps at the appropriate frequency to keep pace with the web and keep the stator one full step ahead of the rotor.
In our last posting we introduced torque motors and posed the question about how we might be able to modify our new “Hybrid” drive to act like a torque motor.
Have you thought of a way to do it?
Our last few posting introduced a number of improvements to our original stepper drive so we renamed it a “Hybrid” drive. This “Hybrid” drive operates in all four quadrants without missing any steps and without stalling. Think about that for a minute. A stepper system that doesn’t stall, when’s the last time you heard that?
Our last posting introduced the idea of four quadrant drives. Four quadrant drives allow the motor to generate torque in the same direction or in the opposite direction that the shaft is spinning. If the motor is operating in the first or third quadrant the rotor will lag the stator’s magnetic field. If the motor is operating in the second or fourth quadrant, then the rotor is leading the stator’s magnetic field. In either case, the maximum torque that a stepper can generate is when it’s lagging or leading the stator’s commanded position by one full step.
Our last posting we introduced the idea of “position make up.”
The idea is that we’re using the 1.1 full step rotor-stator lag information and making a choice as to whether or not the drive will send all the steps it has received to the stator.
We left off last time with a new “Hybrid” drive that controls the magnitude of the motor’s current based on how large the rotor lagged behind the commanded step position.The larger the lag the more current is pumped into the winding to try to keep it from lagging more. It’s a linear relationship. If the rotor lags by ¼ of a full step then the winding current is approximately ¼ of 2 amps or ½ an amp. If it lags by ½ of a full step then the current is 1.0 amp.
In our last blog I was about to call my local garage and make an appointment to have the 100,000 mile checkup which includes an oil change and replacement of the timing belt, among other things.