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Kinematics – Actuation of Machines: Part I – Electrical Actuation

written by: naveenagrawal • edited by: Swagatam • updated: 7/28/2009

Every machine is made to perform and produce some useful work. To make any machine work or to give output it needs to be actuated. Actuation of a mechanism or machine means to input mechanical work into it which is in turn transformed into the desired useful work output by the machine.

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    Actuation of Machines

    A machine is an integration of different mechanisms designed and assembled such that they can perform required work. The linkages and mechanisms inside the machine transfer the input mechanical work from the input point or generating site to the point where a useful effect is produced. Actuation means providing that required mechanical work for input. An actuator is a device, mechanical or electrical, which generates the required mechanical work in controlled manner.

    Machines for printing and packaging, which perform the same task repeatedly at very high production rates, are generally powered by single motor called a prime mover and all the sub-functions are carried out by various linkages. This prime mover can be a large electric motor, an internal combustion engine, a steam engine or a turbine.

    Advancements in actuator technology have resulted in a number of compact and precisely controllable actuating devices. The most commonly used actuators are:

    • Electrical Actuators
    • Hydraulic Actuators
    • Pneumatic Actuators

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    Electrical Actuators

    Today a wide variety of electrical actuators are available using new advanced power switching technologies which have resulted in greatly enhanced performance. Commonly used electrical actuators:

    Electric motors: Electric motors have a rotating shaft which produces angular rotation and torque. Electric motors can operate at very high speeds which can be reduced to get proportional increase in torque by means of a mechanical gear assembly or transmission. There are basically three types of electric motors.

    1. DC Motors or Commuted Motors.

      They operate on Direct Current and have commutators to switch the current carrying coils so that the rotation of the shaft is in same direction.

      2. AC Motors or Non-commuted Motors.

        They operate on Alternating Current and do not need commutators for operation.

        3. Stepper or Stepping Motors.

          These motors have equally spaced discrete movements called as steps. Stepper motors are turned by feeding voltage pulses to it which can be controlled by stepper motor controller to determine the step size or amount of rotation for each pulse.

          Electric motors when used as actuators can be assisted by a feedback controller to keep track of the position and make necessary corrections in input accordingly.

          Solenoid: Solenoid has a cylindrical winding and a ferromagnetic core in and along the axis of this cylindrical winding. When this winding is supplied with direct current the ferromagnetic core is pulled inside the cylindrical winding. Thus, a solenoid is a two-state actuator.

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          Electrical Actuator Control

          Electrical Actuators can be controlled to get optimum performance by using solid-state power-switching devices. Earlier methods for control of DC motors had inherent energy loss as they use potentiometers. Modern control devices such as pulse-width modulators and phase-controlled rectifiers can control DC motors without energy losses. The new control devices has made actuators more compact but at the same time the control unit may even cost more than the actuator itself.