Difference between revisions of "Drive fault handling"

Revision as of 00:08, 1 August 2015

All Granite Devices drives share similar fault handling and recovery from faults. This page describes how faults are triggered and handled.

Types of faults

A fault can be a condition measured by drive that exceeds user set, or fixed threshold, such as:

• Operating condition out of allowed bounds, such as under voltage, over voltage, over temperature
• Drive has measured excessive current at motor outputs, can be either
  • User adjustable over current limit (this is typically 10-100% above motor maximum current parameter MMC). The tolerance level is adjusted by parameter FOC.
  • Short circuit (fixed limit defined by hardware, typically several times higher than drive's maximum current rating)
• Goal faults, such as tracking error, over speed or travel beyond allowed boundaries (limit switch hit)
• Etc

Faults are indicated by device LED blinking sequence as well as configuration tool status dialog. In Granity, it's recommended to look at Testing tab status bits and Fault location to identify the source of error.

Reaction to fault

In most fault cases drive will enter in fault state which will:

• Disable motor control
• Brake motor if possible (dynamically and with mechanical brake)

The purpose of reaction is to protect damage from happening to machine operator, drive or machine. All fault stops are latching, meaning that drive will wait for recovery command after fault before attempt of recovering.

Recovery from fault

Drive will start recovering from fault after clear faults command:

• Digital signal to clear faults input (drive dependent). Sometimes this may be combined to enable signal, which meaning that rising or falling edge of enable signal will clear fault state.
• Software command (via SimpleMotion interface). Can be triggered from configuration tool or user application.

After clear faults, drive resets the fault state and attempts to recover to the original state. This means re-enabling motor control and a new attempt to follow the actual setpoint. Fault recovery depends on control modes being used:

Torque mode

Drive attempts to continue producing torque as defined by current setpoint

Velocity mode

Drive attempts to accelerate to the target velocity as defined by current setpoint

Position mode

Drive attempts to move back to the commanded position (setpoint). Motion happens at user defined error recovery velocity CRV, which is usually set lower than than the maximum velocity limit CVL. If no recovery motion is desired (drive should stay at position where it faulted), then set CRV parameter to zero.

Drive will continue listening the change of setpoint during fault stop state. I.e. if drive is in step/direction mode and step pulses arrive during the fault, drive will resume to the position defined by the latest setpoint.

Managing faults from controller

Controller should:

• Monitor state of drive either by monitoring the fault output signal (digital output) or polling status register of drive (through SimpleMotion)
• When fault state is active, cease changing setpoint or set it to a value that is desired after recovery
• Issue the clear faults command through digital input or SimpleMotion command

Troubleshooting

1. If drive will stay infinitely or too long in error recovery mode (can be identified by LEDs and configuration tool status info), it is typically caused by constantly changing setpoint value. In such case drive is chasing the varying setpoint but never reaches it (typical especially with analog or PWM setpoint mode where noise can alter the setpoint, or when controller do not cease sending new setpoint values until drive is recovered). As countermeasure try increasing CRV value or stabilize the setpoint.