Difference between revisions of "Essential Basics"

Revision as of 10:00, 27 July 2018

These basics are the most fundamental steps to get a motor running in order for an application to work properly.

1. Motor supply voltage (HV) can be higher than nominal motor voltage
   • Digital servo drives are practically sophisticated switching step-down voltage regulators, and the torque controller takes care that the current to the motor (and thus the voltage) is correct.
   • The HV can be at least five times the nominal motor voltage without any issues and reduced performance.
2. The maximum current to the motor is not the maximum current rating of the PSU
   • Considered as a step-down regulator, the digital servo drive transfers power, not current to the motor. Because of this, the PSU's current rating affects maximum power that can be driven into a motor, not maximum current.
   • In ideal world, e.g. 48 V PSU with 10 A current rating can output 480 W power. If the required voltage to a motor to drive 24 A current is 20 V, the transferred power is the same what the PSU can supply.
3. Encoder must be attached directly to the motor shaft
   • In practice, all gears and other such mechanics have non-idelities such as play, torsion, and/or possibility of slipping.
   • Play and torsion will introduce delay to the feedback loop, and will cause oscillation due to which the tuning is impossible to get precise.
   • Slipping encoder will give false data, which will cause the motor to either stall or run loose.
   • Encoder resolution must be exact for each rotation. Rounded data will also cause the known magnetic angle to be lost, and the motor will stall or run loose after few turns.
4. Phasing
   • If hall sensors or absolute encoder are not used, the motor needs to be rotated/moved to find a known magnetic angle. Only after this the encoder can give reliable information of the motor position so that it can be controlled properly.
   • If phasing is not done correctly in free motion, the motor can not be controller properly.
5. STO (Safe Torque Off) and Enable
   • If SimpleMotion is not used, STO and Enable must be wired physically
   • In Granity 1.14.0 and later, both can be ignored for tuning.
6. Torque tuning must be done properly
   • Poor torque tuning will result in excessive current spikes and at worst mechanical oscillation.
7. Testing motor and encoder wiring in torque mode
   • Before velocity or position tuning, the system must be tested without any load in torque mode to ensure proper functionality.
   • Follow the instructions here: Servo motor torque mode test.