Tracking error

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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[edit | edit source]

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 Position tracking error thresholdFPT and Velocity tracking error thresholdFVT parameters.

Fault countermeasures[edit | edit source]

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 Invert feedback directionFBI setting.
    • If motor type is AC/BLDC, then feedback resolution Invert feedback directionFBI and pole count Pole countMPC 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 Pole countMPC and Feedback device resolutionFBR. If unsure, contact support with attached feedback device and motor data sheet.
  • Too low fault tolerance levels → Increase Position tracking error thresholdFPT, Velocity tracking error thresholdFVT and/or Goal faults filter timeFFT 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 Acceleration limitCAL OR increase motor current limits, especially Peak current limitMMC
    • Too fast velocity → reduce velocity limit Velocity limitCVL. 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)

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