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Servo commissioning & tuning
Commissioning a servo system: checklist, auto-tuning and homing
Running a servo axis for the first time is a matter of sequence: wiring checks, motor and encoder match, direction and limits, then tuning and homing. A skipped step comes back later as vibration and position error.
6 questions answered
Basics
Commissioning
Commissioning
01
In what order should I bring up a servo axis for the first time?
The safe order is: check the wiring before power (U/V/W order, PE, encoder, brake), power the drive and confirm it recognises the motor and encoder type, jog the motor at low speed before it is coupled to the mechanics, test the direction and the limit switches, then couple it and run auto-tuning and homing.
How is auto-tuning done, and why does the inertia ratio matter?
Auto-tuning is the drive moving the axis in short strokes, measuring the load inertia and choosing gains to match, so the axis must have its real load attached and room to move freely. The larger the ratio of load inertia to motor inertia, the softer and more resonance-prone the system becomes; on highly dynamic axes a gearbox or a higher-inertia motor keeps that ratio small.
Make sure there is nothing the axis can hit during tuning
If the result is not enough, raise the rigidity setting one step and retry
Tune from the inside out: the speed loop first, then the position loop. Raise the speed gain until vibration starts, then back off a little; shorten the integral time until the axis settles with no remaining error. Raise the position gain last, as far as it gives the fastest settling without overshoot.
Change one thing at a time and watch the drive's trace
Homing ties the axis's zero to a physical reference on the machine. The most precise method uses the encoder's first index (Z) pulse after a reference switch; running to a limit switch or to a hard stop with limited torque are simpler options. In CiA 402 the method is selected with object 0x6098. On axes with an absolute encoder, zero is set once and no homing is needed at every power-up.
What is the difference between absolute and incremental encoders? What is BiSS?
An incremental encoder only counts how far it has moved; after a power loss it does not know where it is, and homing is needed at every start. An absolute encoder reports the true position the moment it powers up, and multi-turn types also keep the revolution count. BiSS is an open encoder protocol that sends the absolute position to the drive digitally over a serial link. The SM motors come with BiSS and incremental encoder options.
The encoder cable must match the motor's encoder type (BiSS or incremental)
How do I set brake timing on a motor with a brake (vertical axis)?
A motor brake is a holding brake, not a stopping brake. At start the drive must energise the motor and build torque first, then release the brake; at stop it must apply the brake, wait for it to engage mechanically, then remove motor power. These delays are drive parameters, and if they are wrong a vertical axis drops a little.
Supply the brake coil through the drive's brake output or a relay
On a vertical axis, STO and the brake must be designed together from the risk assessment
