Motor controller

From Wikipedia, the free encyclopedia

A motor controller is a device or group of devices that serves to govern in some predetermined manner the performance of an electric motor. A motor controller might include a manual or automatic means for starting and stopping the motor, selecting forward or reverse rotation, selecting and regulating the speed, regulating or limiting the torque, and protecting against overloads and faults.

Contents

[edit] Scope of motor controller applications

The scope of motor control technology must be very wide to accommodate the wide variety of motor applications.

[edit] Domestic applications

Electric motors are used domestically in personal care products, small and large appliances, and residential heating and cooling equipment. In most domestic applications, the motor controller functions are built into the product. In some cases, such as bathroom ventilation fans, the motor is controlled by a switch on the wall. Some appliances have provisions for controlling the speed of the motor. Built-in circuit breakers protect some appliance motors, but most are unprotected except that the household fuse or circuit breaker panel disconnects the motor if it fails.

[edit] Office equipment, medical equipment etc.

There is a wide variety of motorized office equipment such as personal computers, computer peripherals, copy machines and fax machines as well as smaller items such as electric pencil sharpeners. Motor controllers for these types of equipment are built into the equipment. Some quite sophisticated motor controllers are used to control the motors in computer disc drives. Medical equipment may include very sophisticated motor controllers.

[edit] Commercial applications

Commercial buildings have larger heating ventilation and air conditioning (HVAC) equipment than that found in individual residences. In addition, motors are used for elevators, escalators and other applications. In commercial applications, the motor control functions are sometimes built into the motor-driven equipment and sometimes installed separately.

[edit] Industrial applications

Many industrial applications are dependent upon motors (or machines), which range from the size of your thumb to the size of a railroad locomotive. The motor controllers can be built into the driven equipment, installed separately, installed in an enclosure along with other machine control equipment or installed in motor control centers. Motor control centers are multi-compartment steel enclosures designed to enclose many motor controllers. It is also common for more than one motor controller to operate a number of motors in the same application. In this case the controllers communicate with each other so they can work the motors together as a team.

[edit] Vehicle applications

All types of engine-driven vehicles from automobiles, airplanes, aircraft carriers and agricultural equipment to zambonis may have electric motors to perform a variety of functions. In electric vehicles, diesel-electric vehicles, and hybrid vehicles, electric motors are used to propel the vehicle. The motor controllers in vehicle applications are integrated into the vehicle.

[edit] Power tools

Power tools such as drills, saws and sanders are widely used by home owners, hobbyists, construction and repair trades people, and industrial workers. Both portable and stationary power tools usually have built in motor controllers and often include an adjustable speed feature.

[edit] Hobby equipment

A variety of hobbies make use of specialized motorized equipment that is similar to domestic appliances or portable tools.

Radio controlled (R/C) models may include fairly sophisticated motor controllers. The motor controllers are ultimately built into the equipment, but the hobbyist may purchase the controller separately or construct it.

Robotics is another area in which the hobbyist may purchase a motor controller as a separate item or construct it.

[edit] Types of motor controllers

An electric motor controller can be classified by the type of motor it is to drive such as permanent magnet, servo, series, separately excited, and alternating current.

A motor controller is connected to a power source such as a battery pack or power supply, and control circuitry in the form of analog or digital input signals.

[edit] Specific motor controller descriptions

[edit] H-bridge

DC motors are typically controlled by using a transistor configuration called an "H-bridge". This consists of a minimum of four mechanical or solid-state switches, such as two NPN and two PNP transistors. One NPN and one PNP transistor are activated at a time. Both NPN or PNP transistors can be activated to cause a short across the motor terminals, which can be useful for slowing down the motor from the back EMF it creates.

[edit] Servo controllers

Most servos are controlled using pulse-width modulation (PWM). How long the pulse remains high (typically between 1 and 2 milliseconds) determines where the motor will try to position itself. The controller must know the motor's position in order to know how to move it. To find the position of the motor some designs use Hall effect sensors to directly measure the rotor's position. Others measure the back EMF in the undriven coils to infer the rotor position, eliminating the need for separate Hall effect sensors, and therefore are often called "sensorless" controllers. A variable resistor can also be used to determine the motor's position.

[edit] Stepper motor controllers

Stepper motors are moved by rotating which coil to apply electricity to in a circular manner. They are controlled by a timing circuit. This allows extremely accurate control by changing the clock speed for the next firing. Typically these are used in printers where precise positioning is necessary and must be done in the cheapest way possible.

[edit] References

[edit] Software

[edit] See also

Retrieved from "http://en.wikipedia.org../../../m/o/t/Motor_controller.html"