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Industrial Robots Programming - J. Norberto Pires Part 5

Tham khảo tài liệu 'industrial robots programming - j. norberto pires part 5', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Robot Manipulators and Control Systems 71 up to the base speed. After that it is still possible to increase the velocity by changing p but the motor enters the field-weakening mode and any increase in speed is done at the expense of the peak torque. Torque Base Speed Speed Figure 2.16 Torque-Speed characteristic of a sine wave motor The natural relations for the back-EMF E and for the torque T used for a DC square wave motor still hold for a sine wave motor i.e. T kt I E ke wm 2.95 . . kt a 3 but now with -m- 1. ke 2 The torque constant kt and the back-EMF constant ke can be measured using the following equations ke V-s rad wm 2.96 where ẽLL is the peak line-line voltage and wm is the mechanical angular velocity. kt Ị Nm 2.97 i where i is the peak line current when the motor is in normal operation measured using a current sensor connected to measure the phase current directly and then displayed in an oscilloscope. It is also possible to write 72 Industrial Robots Programming - ê a 3 - a 3 - I- T.wm kt ĩ - - èLL ĩ - V2 ERMS V2 IRMS ke 2 2 2.98 VĨ ERMS 1 MS Electrical - Mechanical Power Conversion and 3 erms rms 1. tT _ V _ 3 erms -------------------- Kt 1RMS Kt ---- Wm 27t v RPM 60 2.99 2.6.1 Motor Drive System In this section the main circuits necessary to drive a three-phase AC synchronous PM motor are briefly presented. As already mentioned a brushless AC PM motor requires alternating sine wave phase currents because the motor is designed to generate sinusoidal back-EMF. The power electronic control circuit is very simple and uses some control strategy12 to achieve torque smooth speed and accurate control keeping the current to a safe value. In order to obtain sine wave phase currents the power supply DC voltage must be switched on and off at high frequency under the control of a current regulator that forces the power transistors to switch on and off in a way that the average current is a sine wave. Basically the sine wave reference signals could just be applied