maxon motor control Technology − short and to the point
Controllers The maxon motor control program contains servo amplifiers for controlling the fast reacting maxon DC and EC motors. Special characteristics: − built-in additional inductance for operation with low-inductance motors. − high PWM frequencies (>50 kHz) − high efficiency The zub machine controllers are program- mable master controllers for sophisticated multi-axis systems − EtherCAT and/or CANopen master (and/or slave) − Highly dynamic drive synchronization − Curve interpolation (camming) Set value specification Servo controllers (speed and current control- lers) are usually designed for analog specifica- tion of set values. Alternatively, PWM signals or fixed set values are also possible. maxon positioning controllers (EPOS) require a higher-level master, which takes care of pro- cess control and sends individual commands to the positioning controller and to other slave modules in the system via the bus system (RS232, USB, CANopen, EtherCAT). Typically, the master reads the parameters of the slave modules (e.g., the current position or the status of an input), and uses them to generate new commands (e.g., a new target position or set- ting of an output). The master runs an applica- tion specific program. Possible master systems − zub motion control − PLC − Microcontroller − PC
Program − DEC module: 1-Q speed controller (closed loop) for brushless (maxon EC) motors − ESCON: 4-Q speed and current controller for DC and EC motors − EPOS: Position controller for DC and EC motors − MACS5, MiniMACS, MasterMACS: Programmable multi-axis masters
Motor type − maxon DC motor − maxon EC motor Control variables − Speed − Position − Current Feedback − Encoder − DC Tacho − IxR compensation − Hall sensors Set value specification − Analog voltage − Digitally via field bus with or without sensor
Controlled variables Speed control
Feedback sensors Digital encoder control
The function of the speed servo amplifier is to keep the prescribed motor speed constant and independent of load changes. To achieve this, the set value (desired speed) is continuously compared with the actual value (actual speed) in the control electronics of the servo amplifier. The controller regulates the power stage of the servo amplifier to eliminate this difference as much as possible. The control loop is closed. Position control The position controller ensures that the currently measured position matches a set position, by sending appropriate correction values to the power stage, just like the speed controller. The required position information is usually received from a digital encoder. Current control The current control provides the motor with a current proportional to the set value. Accor- dingly, the motor torque changes proportionally to the set value. The current controller improves the dynamics of a higher-level position or speed control loop.
The motor is equipped with a digital encoder that provides a certain number of pulses per revolution. Incremental or absolute encoders can be used (cf. p. 74: Encoder signals). − Digital encoders are often found in positioning controls, in order to derive and measure the travel or angle. − Digital encoders are not subject to mecha- nical wear. − If an EC motor's Hall sensor signals are used for control, then the result is similar to using an incremental encoder with a low resolu- tion.
Principle of a control circuit
Set value
System deviation Con- troller
USB
Motor
Power stage (actuator)
Actual value
Sensor
76 Technology – short and to the point
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