Servo Motor Advice

[graemeian 2]

I need advice on choosing a servo motor. I need the following parameters. If one coupled a disk to the end of a servo motor with an inertial load of the disk to be 0.01 kg m2. I want to start at a position, call it 0 degrees, spin the motor shaft 180 degrees, then reverse it back to 0 degrees. Call each single motion a cycle. What is the fastest cycle rate one can perform? I need something in excess of 10 Hz. What motor would be best? Now, what if each cycle is a different angle always less than 180 degrees. I need a controller that can give the motor these commands. I am leaning towards an AC motor. It will require about 5 Hp. Any suggestions? Thank you.

[Leitmotif 0]

I do not think your problem will be in the motor but in the sensing. What is your tolerance for teh 0 and 180 positions? Does the motor have to hold that position - any drift allowed? In other words how precisely must you stop the motor at a position? If you tolerance was say + - 10 degrees then you could possibly do it with off shelf VFD motor and encoder?? Dan Bentler

[paulengr 44]

Have you decided on a torque profile? A simple trapezoidal profile or even triangular profile makes it very easy to calculate your torque and speed requirements. Without those it is difficult to specify a motor by itself. Given that you are asking to make a move of 360 degrees 10 times per second, this corresponds to 10 rotations/sec. Even if the motor spends twice that long speeding up and slowing down, that is 20 rotations/sec, or 1200 RPM. This is very much within the requirements of most motors, AC or otherwise. If you are following a triangular torque profile and you've already specified the inertia, it should be easy to calculate the torque requirement (which is a constant), and hence the required motor HP (or kw if you prefer those units). There may be more torque required if you need holding functions and such. Beyon this it's a matter of picking a motion controller and amplifier (aka servo drive) that supports the type of motor you desire. Some PLC's (if you are using one) can run servo systems directly, and vice versa, some servo controllers also include PLC functions. So don't forget to include these parameters in your design. Note that "AC" is somewhat confusing in terms of terminology. A standard squirrel cage induction motor is of course "AC" but if you use one of these, you'd need external cooling for temperature control. There are also brushless servo motors which can be AC or DC. Permanent magnet DC motors (aka "universal" motors) can have advantages at times so don't count out the slightly higher maintenance cost with them. You might even be able to use a simple stepper motor, or if you think in terms of linear vs. rotary motion, you might be able to achieve the required motion with just a linear actuator instead. In terms of how fast you can jerk back and forth in an oscillating motion, lasers often use a very specialized motor called a "galvanometer scanner" which is effectively just a solenoid (galvanometer) pressed into service as a motor but the rotational range is very restricted (1 or 2 degrees at most). Coupling two of these together creates an XY scanner...a laser projector which can be steered anywhere in a rectangular area. Adding a special electrooptical prism creates color control.