Several installation positions of encoder in motion control

The encoder at the end of the motor first feeds back signals to the motor driver.

The encoder at the end of the variable frequency motor provides speed closed loop feedback to the inverter.

The encoder at the end of the servo motor provides closed-loop position feedback to the servo drive. The advantage of installing an encoder at the end of a variable frequency motor is that it directly reflects the dynamic performance of the motor speed, as a closed loop for phase frequency current torque acceleration motor drive speed regulation vector control.

The encoder at the end of the variable frequency motor is the speed closed loop of the frequency converter speed regulation. If the inverter does have a PG card, it is only a closed loop of speed regulation, the position loop of the upper computer (PLC, etc.) depends on the speed on the time axis. complete.

If the PG card of the position control card is added to the inverter, the closed-loop control of the motor position can be realized directly on the inverter. However, variable frequency motors rely on mechanical transmission to drive the load side. This kind of closed-loop motor position is only reflected in the position value when the motor rotates at a high speed, the actual position of the low-speed load end after the transmission is decelerated. This closed loop position is called a semi-closed loop. Due to the use of variable frequency motor decelerating transmission device, this closed loop error is relatively large.

Therefore, the end encoder of the variable frequency motor (including the asynchronous servo motor with servo function) is basically based on the speed closed loop the incremental encoder.

Encoder on servo motor: Servo is a natural position closed loop. The design of the servo motor is a closed loop of position, speed current torque. The encoder synchronously feeds back the position of the motor rotor differentiates it with the speed loop on the time axis. Therefore, regardless of whether the speed loop priority position loop priority control strategy is adopted, the original information feedback the encoder to the servo controller is the position loop.

This kind of closed loop is a closed loop for the motor. It truly reflects the speed phase of the motor on the speed. It is helpful for the transmission to quickly adjust the transmission according to the feedback, but the terminal position control after the transmission is semi-closed. The mechanical transmission Is detached:

1 The uncertainty of the multi-stage mechanical transmission gap error the uncertainty of the transmission "elasticity" caused by load changes;

2 Transmission mechanical abrasion debugging running-in period are long, there is no feedback on the mechanical damage that may occur to the transmission, resulting in uncertain safety. Due to the inevitable positioning error due to the above-mentioned uncertainty, the parameter debugging during the debugging process is uncertain, the technical personnel need to adjust the parameters again after the trial operation, which greatly increases the labor cost of the debugging.

three. The origin position is lost. At present, most of the servo motor tail encoders are incremental encoders single-turn absolute encoders. Mechanical absolute multi-turn encoders are large in size, with a range of 4096 revolutions, which is often enough for actual motors. Number of revolutions. At present, the absolute value mechanical multi-turn encoder is rarely installed directly at the tail of the servo motor. At present, the incremental encoder at the end of the servo motor relies on the addition of an origin switch at the mechanical end, the single-turn absolute encoder relies on a multi-turn counter to store the accumulated value, uses various methods to store data after power failure. This includes Wiegand coils that use batteries, super capacitors weak self-generated electricity. But in fact, these are true absolute multi-turn codes. Once they are disturbed during the counting of accumulated turns, when weak low-power operation is detected after power failure, they will be disturbed when monitoring the change of turns (encoder power-off low-power operation), when the signal is very weak , The probability of interference increases). Once disturbed, the number of revolutions is incorrectly added, it is impossible to judge. This will cause a loss of origin error. Therefore, using a single-turn absolute value as a multi-turn encoder loses the meaning of “absolute value” because there is still the possibility of losing the origin. But compared with incremental encoder, the probability of losing the origin is greatly reduced.