Three methods for PLC control of servo motors:
I. Torque Control
II. Position Control
III. Speed Mode
I. Torque Control
Torque control is achieved by setting the output torque of the motor shaft through external analog input or direct address assignment. For example, if 10V corresponds to 5Nm, the motor shaft output will be 2.5Nm when the external analog input is set to 5V. If the motor shaft load is less than 2.5Nm, the motor will rotate forward; if the external load is equal to 2.5Nm, the motor will not rotate; and if the load is greater than 2.5Nm, the motor will rotate in reverse (this usually occurs under gravity load).
The torque setting can be changed in real time by altering the analog quantity settings, or it can be achieved by changing the value of the corresponding address via communication.
II. Position Control
Position control mode typically determines the rotation speed by the frequency of externally input pulses and the rotation angle by the number of pulses. Some servos can also directly assign speed and displacement values via communication.
Because position mode allows for very strict control over both speed and position, it is generally used in positioning devices.
3. Speed Mode
Rotation speed can be controlled by analog input or pulse frequency. In the outer loop PID control with a host control device, speed mode can also be used for positioning, but the position signal of the motor or the position signal of the direct load must be fed back to the host for calculation.
Taking the SINAMICS V90 system as an example
SINAMICS V90 comes in two versions depending on the application:
1. Pulse sequence version (integrates pulse, analog signals, USS/MODBUS)
2. PROFINET communication version
The SINAMICS V90 pulse version can realize the internal positioning block function, and also has pulse position control, speed control and torque control modes.
The figure below shows the default interface definition in Pulse Train Instruction (PTI) mode, which conforms to standard application practices.
Only one pulse input channel is allowed to be used at a time. Other control signals can also be freely assigned to the digital input and output terminals. Please refer to the operation manual.
Digital input, supporting both NPN and PNP types. The 24V power supply in the wiring diagram is as follows:
(1) 24V power supply for SINAMICS V90. All PTO signals must be connected to a controller that uses the same 24V power supply, such as SINAMICS V90.
(2) Isolated digital input power supply, which can use the controller power supply.
(3) Isolated digital output power supply, which can use controller power supply.
SINAMICS V90 Servo Driver
Motor brake signal (for SINAMICS V90 200 V drive only). The SINAMICS V90 200 V drive requires an external relay to connect the motor brake.
System wiring diagram for SINAMICS V90 pulse sequence version
System wiring diagram for SINAMICS V90 PROFINET version
1. SIMOTICS S-1FL6 low inertia motors SH20, SH30 and SH40 use cable-type connectors.
2. The brake cable connection shown here is only applicable to the V90 400 V drive. The V90 200 V drive requires the use of an external relay to connect the motor brake cable.
3. The SINAMICS V90 PTI drive must be connected to the relay via the setpoint cable, while the SINAMICS V90 PROFINET drive is connected to the relay via the I/O cable.
4. I/O cables must be used to implement brake control driven by SINAMICS V90 PROFINET 200 V, and to implement applications that require additional DI/DO in addition to PROFINET communication.
