Servomotors伺服电机的原理和应用

Figure 11-85 shows three types of voltage waveforms that can be used to power the brushless servomotor. Figure ll-85a shows a trapezoidal EMF (voltage) input and a square wave current input. Figure ll-85b shows a sinusoidal waveform for the input voltage and a square wave current waveform. Figure ll-85c shows a sinusoidal input waveform and a sinusoidal current waveform. The sinusoidal input and sinusoidal current waveform are the most popular voltage supplies for the brushless servomotor.

FIGURE 11-85 (a) Trap-ezoidal input voltage and square wave current wave-forms. (b) Sinusoidal in-put voltage and sinusoidal voltage and square wave output voltage wave-forms. (c) Sinusoidal in-put voltage and sinusoi-dal current waveforms. This has become the most popular type of brushless servomotor control.

Figure 11-86 shows three sets of transistors that are similar to the transistors in the output stage of the variable-frequency drive. In Fig. ll-86a the transistors are connected to the three windings of the motor in a similar manner as in the variable-frequency drive. In Fig. 1 l-86b the diagram of the waveforms for the output of the transistors is shown as three separate sinusoidal waves. The waveforms for the control circuit for the base of each transis-tor are shown in Fig. ll-86c. Figure ll-86d shows the back EMF for the drive waveforms.

FIGURE 11-86 (a) Tran-sistors connected to the three windings of the brushless servomotor. (b) Waveforms of the three separate voltages that are used to power the three motor wind-ings. (c) Waveforms of the signals used to control the transistor se-quence that provides the waveforms for the previous diagram, (d) Waveform of the overall back EMF.

Servomotor Controllers

Servomotor controllers have become more than just amplifiers for a servomotor. Today servomotor controllers must be able to make a number of decisions and provide a means to receive signals from external sensors and controls in the system, and send signals to host controllers and PLCs that may interface with the servo system. Figure 11-87 shows a picture of several servomotors and their amplifiers. The components in this picture look similar to a variety of other types of motors and controllers.

FIGURE 11-87 Example servomotors and ampli-fiers.

Figure 11-88 shows a diagram of the servomotor controller so that you can see some of the differences from other types of motor controllers. The controller in this diagram is for a DC servomotor. The controller has three ports that bring signals in or send signals out of the controller. The power supply, servomotor, and tachometer are connected to port P3 at the bottom of the controller. You can see that the supply voltage is 115-volt AC single phase. A main disconnect is connected in series with the LI wire. The LI and N lines supply power to an isolation step-down transformer. The secondary voltage of the trans-former can be any voltage between 20 and 85 volts. The controller is grounded at terminal 8. You should remember that the ground at this point is only used to provide protection against short circuits for all metal parts in the system.