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Reliability / Failure Management

System reliability, safety and failure management are important details when products are designed. No matter the operating condition or environment, the product should implement technology to maintain stable operation. In case of unavoidable faults, failure management should implement functions with highest regards to the safety of personnel, machine, and product. Many advanced features to quickly detect and safely react to these situations are designed into DMM products.

1. Absolute Encoder CRC Code
By using the security code in the new ABS-16 series absolute encoder feedback package, the servo drive will declare and trigger the encoder or encoder connection failure alarm after a certain amount of security code errors.

If the received packet data or CRC is not correct, the servo drive has unique algorithm to still allow reliable, uninterrupted operation. Within 2.5ms, the servo will be stopped if an irresolvable number of errors is detected. Very high encoder feedback reliability is maintained after checking the CRC code.

2. DIPM Hardware Over-Current Detection
DIPM has dedicated hardware control logic circuit for over-current monitor to detect internal or external abnormal/short circuit. Once abnormal current is detected, the hardware logic circuit will disable the module within 10µs. Response is faster for sharper rise of collector pulse current (short circuit case).

This dedicated hardware circuit responds independently from servo control software to achieve highest priority to safely shut down DIPM as fast as possible. The drive, motor and external components are protected from possible damage, shock or other hazards.

3. DYN Servo Over-Power / Over-Heat
By calculating the power transferred to motor by the servo drive over a continuous period of time, then evaluating whether the output power exceeds the rated power, we prevent motor and drive from over-power and over heat-failures.

An advanced output power monitor does not interfere with instantaneous peak output of servo motor, which can be up to 3 times rated output. It balances short, high spikes with long continuous draw to maintain continuous operation, while still allowing servo motor to operate in peak torque region.

4. Servo Motor Following Error
The integrator in the servo maintains the following error to be zero, for almost all times. If any abnormally large external disturbance, or any other reason causes motor position error to be too large, the servo algorithm detects and assert alarm.

If, over a certain period of time, the difference between command position and real motor position is over 90deg, the "lost follow" failure will be asserted in the servo drive and a corresponding "lost phase" alarm will be triggered by servo drive.

5. Regenerative Energy Dissipation
During motor deceleration, mechanical energy will become electrical energy. In the DYN4 servo drive, this boosts the internal DC bus voltage. If the internal DC power voltage exceeds threshold DC level (~380VDC), the external regenerative resistor circuit is turned on and extra energy is dissipated. If the internal voltage level is over ~420VDC for a specific period of time, servo drive alarms over-voltage and shuts down.

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