PLC engineer will know - three servo motor control way

Servo motor speed control and torque control is done with analog control, position control is through the pulse to control. What specific USES control mode according to the customer's requirements and to select meet what kind of movement function.

next, to introduce the servo motor of three kinds of control mode.

if you didn't ask for motor speed, position, as long as a constant torque output, of course is to use the torque mode.

if the position and velocity accuracy to a certain extent, and the real-time torque is not very care about, with better speed or position mode.

if the upper controller has better closed-loop control functions, with a speed control effect will be better. If the request is not high, or almost no real time request, in position control mode has no high demands on upper controller.

it seems to the response speed of the servo driver: computation of minimum torque mode, drive the fastest response to control signals; Location model computation, drive the slowest response to control signals.

the dynamic performance of sports have higher requirements, the need to adjust motor in real time.

if the controller itself operation speed slow ( Such as PLC controller, or low end of the motion controller) Way, use the position control.

if the controller operation speed is faster, you can use the speed, the position loop from the driver moved to the controller, reduce the workload of the drive, improve efficiency;

if you have a better host controller, can also use the torque mode control, the speed loop also remove in the drive, this generally only high-end dedicated controller to do so.

drive control is good or bad, is said to have a more intuitive way of comparison, called response bandwidth.

when the torque control and speed control, through the pulse generator to give it a square wave signal, make the motor continuously forward, reverse, constantly by high frequency, the oscilloscope display on a frequency sweep signal, when the envelope peak to peak in 70. 7%, says it has out of step, the frequency of high and low, can show the stand or fall of control, general current loop can do more than 1000 hz, and speed loop can be dozens of Hertz.

1。 Torque control

torque control way is through external analog input or directly address assignment to set the size of the output torque of the motor shaft foreign, embodied in 10 v corresponds to 5 nm, for example, when the external analog set to 5 v motor output shaft is 2. 5 nm: if the motor axle load is lower than 2. 5 nm motor forward, external load is equal to 2. 5 nm motor does not turn, greater than 2. 5 nm motor reversal ( Usually in a gravity load conditions) 。 Can through instant change analog set to change the torque size set, also can through the communication way to change the address of the corresponding numerical values.

applications mainly in has strict requirements on the stress of the material of winding and rolling device, such as spare line or pull fiber optic equipment, the torque of the set according to the change of the radius of the change to ensure that the stress of the material will not change with the change of the winding radius.

2。 Position control

position control mode is generally through the external input pulse frequency to determine the size of the rotational speed, by the number of pulses to determine the rotation Angle, there are some servo may directly by way of communication for assignment speed and displacement. Due to the location mode can have very strict control on speed and position, so generally used in the positioning device.

applications such as nc machine tools, printing machinery, etc.

3。 Speed mode

through analog input or pulse frequency can control the rotation speed, in outer ring with superior control device can also locate speed when the PID control model, but it must be the position signal of the motor or load position signal directly to the upper feedback to do operation.

location model also supports direct load position detection signal, then to the motor shaft encoder only detect motor speed, position signal is directly by the ultimate load of the detection device to provide, this advantage can reduce the middle in the process of transmission error, increase the positioning accuracy of the whole system.

4。 Talk about 3 ring

servo motor is commonly three loop control, the so-called third ring is three closed-loop feedback PID control system. Within the PID loop is current loop, the ring is completely inside the servo drive, drive to the motor with hall device test the output current of each phase, negative feedback to the current set of PID adjustment, so as to achieve the output current is equal to the set current, getting as close as current loop is to control the motor torque, so the minimum drive torque mode of operation, fast dynamic response.

2 ring is speed ring, by detecting the motor encoder signal for negative feedback PID adjustment, its loop PID output is directly within the current ring set, so the speed loop control contains the speed loop and current loop, in other words, any model must be using current loop, current loop is the fundamental control, and at the same time of speed and position control system in the current actual ( Torque) In order to achieve the control of the corresponding control of speed and position.

3 ring is the position loop, it is the outer ring, can be build between the drive and motor encoder can also in the external building between controller and motor encoder or ultimate load, according to the actual situation to decide. Position control loop due to the internal output is the set speed loop, position control mode system for the operation of all the three ring, at this time of system computation, the largest dynamic response speed is the slowest.

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