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Servo motor control ways

    Speed control and torque control are using analog control. Pulse to control the position control is through the hair. Specific controlled by what way according to the requirements of customers, meet what kind of movement function to choose.

    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 torque model is not very convenient, with better speed or position mode. If the host 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 is not high demands for upper controller.

    In the context of 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.

    Have a higher request for dynamic performance of the need to adjust motor in real time. So if the controller itself operation speed slow (such as PLC, or the low end of the motion controller), with the position control method. If the controller operation speed is faster, you can use speed, the position loop from the driver moved to the controller, reduce the workload of the drive, improve efficiency, such as in the most high-end motion controller); If there is a better host controller, can also use the torque mode control, the speed loop also remove in the drive, it generally only high-end dedicated controller to do that, and then completely don't need to use servo motor.

    General said the drive control is good, both each manufacturer to do the best, but now there is a more intuitive way of comparing the response bandwidth. When the torque control or speed control by pulse generator to give him 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 70.7% said is out of step, the frequency of high and low, who can show the products of cattle, the general current loop can be above 1000 hz, and speed loop can be dozens of Hertz.

In a more professional:

1. the 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 shaft when the load is lower than 2.5 Nm is turn, external load is equal to 2.5 Nm motor does not turn, greater than 2.5 Nm when 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.

Applied mainly in has strict requirements on the stress of the material of winding and rolling device, such as spare line device or optical devices, 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: by means of analog input or pulse frequency can control the rotation speed, in the outer ring with superior control devices 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 by directly to the ultimate load to provides a detection device, this advantage can reduce the middle in the process of transmission error, increase the positioning accuracy of the whole system. about 3 ring, servo is commonly three loop control, the so-called third ring is 3 a 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 loop through the detection of 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 actually is working on current (torque) control in order to achieve 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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