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DC & AC Brushless Motors

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TRM is now supplying a great new range of motors to it's customers at great value prices. Optimised to run at their peak performance with TRM's Drives and Control systems.

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DC & AC Brushless Motors

TRM is a specialist in the design and manufacture of Motion Control products and associated equipment for industrial machine and robot control.

TRM Servo Control System

DC brushless servo motors are in reality a type AC servo motor. There are two basic types of AC servo motor depending upon the type of feedback system. These are the hall effect type where the motor is fitted with three hall effect devices that measure the magnetic field strength to determine the exact position of the armature and resolver or encoder feed back type. The resolver type is the most expensive but offers the best performance since the exact position of the armature can be determined. Hall effect type without encoder feed back are typically used in applications such as fans or for conveyor control. Where an encoder is used, the Z pulse (once precise pulse per revolution) is needed to determine the precise position of the armature. Since both the motion controller and the driver need to know the precise position of the armature the encoder signals are fed to both the motion controller and the drive.

Motors fitted with a resolver provide sine and cosine information to the driver which uses this information for internal control purposes and to provide a simulated encoder pulse stream for the motion controller.

Motor

AC servo motors have one major advantage over DC brushed types in that it is possible to induce more current into the armature than is possible with bushed types. It is also possible to reduce the revolving mass of the motor which results in better performance due to better acceleration/de-acceleration. AC servos are often used because they have no brushes to wear out, but often it is the bearing life that is as important as the brush wear. Brushed servo motors offer the lowest "cogging", which is the vibration or movement error around the command position making them ideal for low speed precision applications such as grinding. Of the AC servo motor types resolver with a sinusoidal drive offers to lowest cogging as the armature position is exactly known. At start up hall effect and encoder feedback types often need to move so that the armature position can be determined. The resolver type can resolve the armature position to 1 in 65,536 per revolution (at low speed) but using conventional encoders the position can only be determined to 1 in 10,000. Most servo motor can during acceleration exert as mush as 400% of their rated torque, however the total cycle torque must not exceed the motors rating. Careful design is required to ensure that the motor is not over stressed which can cause the motor to overheat and damage the motor. AC servo motors need to be controlled by the application of three phases using a 6 transistor bridge. Typically the bridges are of MOS-FET or IGBT types. The best quality servo drives produce synthesized sinusoidal 3 phase. The sinusoidal wave form is simulated by the application of Pulse Width Modulation ( PWM ). The frequency of the PWM is normally from 10KHZ to 50KHZ. Transistor and IGBT types need to be run at lower frequencies due to limits imposed by bi-polar transistors. The other common type of drive is the lower cost trapezoidal type. This type produces a trapezoidal wave form which is easier to produce and needs the use of lower PWM frequencies.

The disadvantage with this technique is that it is less precise, more prone to cogging and poor wave shape decreases the motor efficiency and therefore causes the motor to heat. Some drives even use the application of square waves and make no attempt to assimilate the correct sinusoidal wave form. Control of any AC motor is complicated as there is the need to produce three phase sinusoidal wave form and to vary the relation of the phases to control direction of rotation. In contrast Brushed motors do not need a microprocessor or DSP to control them and the drives have only 4 output transistors the relative simplicity is therefore more reliable.

The TRM Motion Controllers are a complete solution:

Controller Mounted in POD Case

Motion Control of 1 to 4 interpolated axes. Man-machine interface. with 16 digital Inputs / 8 digital outputs, expansion capability. Full PLC capabilities. General Motion programme “MAP” included. Easy to program.

PROCUT is a backguage controller for industrial paper guillotines. A PMC2C is used to control the distance that the paper is to be cut at, color display, memory for 100 programs, easy to program, quick cut, push back paper, manual or automatic operation among other facilities.

TRM distributes PROCUT on behalf of Interneational Control Solutions Ltd (ICS). PRO-CUT is the latest innovation in the guillotine backguage control market. Usually supplied as a complete kit which includes a Control Panel, Electrical Cabinet, Cables, Sensors, Software, Motor, Pulleys, Belts, Motor and Sensor Bracket. For durther infomation please see here.

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