Difference between revisions of "Tracking error"

Revision as of 11:40, 15 April 2015

Tracking error means the difference between the setpoint and measured actual output value. For example in a linear axis tracking error can be the distance between setpoint position and the position where axis really lies at the given moment.

Tracking error fault

In modern motor drives it's possible to define the permissible maximum value of tracking error which is allowed before drive enters in a fault state and stops. Tracking fault is useful for protecting the machine or users from damage if something is preventing mechanism from moving. In Granity this value is entered in FPT and FVT parameters.

Fault countermeasures

Tracking error fault is probably the most common fault in servo motor systems. Typical reasons and counter measures are:

• Wrong motor settings:
  • If motor jumps without command after start-up, the issue probably is wrong feedback counting direction → try changing FBI setting.
  • If motor type is AC/BLDC, then feedback resolution FBI and pole count MPC must be correctly entered. If not, then symptoms are that motion is limited to narrow range to both directions from starting location and going beyond certain point causes tracking error fault → Check MPC and FBR. If unsure, contact support with attached feedback device and motor data sheet.
• Too low fault tolerance levels → Increase FPT, FVT and/or FFT parameters
• Bad servo tuning → Adjust feedback gains, see Servo motor tuning guide
• Asking too much out of motor so motor can't keep up with motion:
  • Too fast acceleration → reduce acceleration rate CAL OR increase motor current limits, especially MMC
  • Too fast velocity → reduce velocity limit CVL. If motor can't reach it's full speed, reason may be too low drive supply voltage or partial loss of encoder signal (encoder not being able to operate at such speeds or interference/bad wiring is causing the error)