I. IntroductionII. General motorIII. Stepper MotorIV. Stepper motor Block DiagramsV. Stepper motor Control aspectsVI. Closing the LoopVII. Servo MotorsVIII. Speed ControlIX. Advantages of servo compared TO STEPPERS motorsX. PID Controllers Effect on PerformanceXI. Additional AdvantagesXII. ApplicationsXIII. ConclusionXIV. AcknowledgmentXV. References[4] D.W. Jones, Control of Stepping Motors. (2004 Nov) [Online] http://www.cs.uiowa.edu/~jones/step/XVI. BiographyAbstract—Automation and control systems have becomean increasingly important aspect of industry. Thesesystems allow for machines to run automaticallyminimizing human involvement in their operation. Motorsare often a critical component of these machines. Twospecific types of motors will be discussed further in thispaper. The first is a stepper motor and the second is aservo motor. These motors have many unique benefitsover tradition electric motors. This paper will seek tofurther discuss the control system that is found in each ofthese systems and describe advantages to each. Index Terms—Proportional controlServo motorsStepper motorsClosed loop systemsOpen loop systemsPulse width modulationI. INTRODUCTIONElectric motors have become increasingly useful as oursociety has become more technologically advanced. As asociety we are constantly seeking to produce products that arecheaper and more efficient. The most common way that thisis done is through the development of machines. At the heartof these machines one will often find some form of an electricmotor. As machines grow in complexity motors must evolveto provide the necessary performance the industry requires.The automation industry has become increasing interested inrepeatable position control. Or in other words, being able toprecisely position some component of a machine using amotor was very important to furthering automationdevelopment. To satisfy these needs two types of motors weredeveloped. This paper will further discuss two unique typesof motors: stepper and servo and there role in the automationindustry. II. GENERAL MOTOR A traditional electric motor uses electrical energy to turn ashaft creating movement. A motor is made up of three basiccomponents large magnets, the coils and the armature. Themagnets are attached to the shaft. A series coils surround theshaft. These coils are used to create a magnetic field. Thisfield repels the magnets on the shaft creating torque andcausing it to turn. By turning on and off the coils in aparticular sequence will cause the shaft to spin. Traditionalmotors are able to spin a smooth speed because the power iscontinuous shifting between the coils. III. STEPPER MOTORA stepper motor takes this concept further. By adding acontroller to the motor one is able to control the inputs to thecoils. A controller sends specific pulses to the motor windingcausing the shaft to turn. This process can control the shaftwith a high degree of accuracy. An example of this can beseen in Figure 1. This example uses four coils for simplicityto control the position of the shaft. Fig. 1 By turning on the coils in sequence will cause the shaft to rotate a specificamount. [1]Figure 1 illustrates one complete rotation of a steppermotor. At position 1, we can see that the rotor is beginning atthe upper electromagnet, which is currently active (hasvoltage applied to it). To move the rotor clockwise (CW), theupper electromagnet is deactivated and the rightelectromagnet is activated, causing the rotor to move 90degrees CW, aligning itself with the active magnet. Thisprocess is repeated in the same manner at the south and westelectromagnets until we once again reach the startingposition. However this example is extremely over simplified.An actual stepper motor would utilize 200 coils that could becontrolled in sequence. This would allow for the shaft to bepositioned in 1.8 deg increments. This stepper motor’s shaftwould turn a full circle after it had made 200 discrete steps of1.8 degrees. [2] This is the most basic movement by which astepper motor is controlled. This type of step is termed a fullstep by motor terminology. There are two other steps that canbe made using this type of motor. The first is a half step. This is done by turning on twoadjacent coils at the same time. This causes the magnets onthe shaft to position themselves half way between the twoA Detailed Study of Stepper and Servo MotorControlsJason Flietstra, Student of Calvin College, Enrolled in Engr. 315 Control Systems1coils creating a half step. Further explanation of the shaftmovement can be seen in Figure 2.Fig. 2 The figure above describes how the shaft will move one half step as twoadjacent coils are turned on together. [1]As you can see in figure 2, in the first position only the upperelectromagnet is active, and the rotor is drawn completely toit. In position 2, both the top and right electromagnets areactive, causing the rotor to position itself between the twoactive poles. Finally, in position 3, the top magnet isdeactivated and the rotor is drawn all the way right. Thisprocess can then be repeated for the entire rotation. Makingusing of this technology typical motors controls are actuateto .9 degrees using 400 half-steps. Sometimes extreme situations call for very accurateposition control. When the position of the shaft must beaccurate to less than .9 degrees motors controllers will use aprocess call microstepping. This process is achieved similarlyto half stepping. Two adjacent coils are given power causingthe shaft to rotate in between them. However, in the case ofmicrostepping the unequal amount of current applied to eachcoil will cause the shaft to stop at a distance between theshafts proportional to the difference in the current applied tothe shaft. Using this technique motor manufactures claimthat their motors can have 256 unique positions between eachof the coils. This means that for a motor with 200 coils it willhave over 52000 unique positions within one turn of the shaft.[2]
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