ECE5320 Mechatronics Assignment#01: Literature Survey on Sensors and Actuators Hybrid Stepper Motor

1. ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Hybrid Stepper Motor Prepared by: Randy Shirts 3/10/2006

2. Outline • Reference list • To probe further • Major applications • Basic working principle illustrated • A typical sample configuration in application (application notes) • Major specifications • Limitations • And many more relevant issues in applications (such as, how to choose, cost information, where to buy etc.) ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

3. Reference list • www.ams2000.com/stepping101.html • www.electricmotors.machinedesign.com/guiEdits/Content/bdeee4/bdeee4_1-3.aspx • zone.ni.com/devzone/conceptd.nsf • www.sapiensman.com/step_motor/#hb • www.devicelink.com/mem/archive/01/09/002.html# • http://www.netmotion.com/htm_files/adv_motors.htm#three • http://www.medicaldesign.com/articles/ID/529 ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

4. To explore further (survival pointers of web references etc) • www.solarbotics.net/library/pdflib/pdf/motorbas.pdf • users.pandora.be/educypedia/electronics/motorstep.htm • www.eio.com • www.cs.uiowa.edu/~jones/step/types.html ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

5. Major applications • Medium load • a simple and cost effective design • high reliability • maintenance free (no brushes) • open loop (no feed back device required) • known limit to the 'dynamic position error' • High precision positioning • X,Y,Z Positioning • Printer feeds • Machine parts positioning ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

6. Basic Working Principle Hybrid-Stepper Motor

7. Differences Between PM & Variable Reluctance Stepper Motors • The variable-reluctance motor does not use permanent magnets, so the field strength can be varied. The amount of torque for this type of motor is still small, so it is generally used for small positioning tables and other small positioning loads. Since this type of motor does not have permanent magnets, it cannot use the same type of stepper controller as other types of stepper motors. • The permanent magnet motor can have multiple rotor windings, which means that the shaft for this type of stepper motor will turn fewer degrees as each pulse of current is received at the stator. For example, if the rotor has 50 teeth and the stator has 8 poles with 5 teeth each (total of 40 teeth), the stepper motor is able to move 200 distinct steps to make one complete revolution. This means that shaft of the motor will turn 1.8° per step. The main feature of the permanent magnet motor is that a permanent magnet is used for the rotor, which means that no brushes are required. The drawback of this type of motor is that it has relatively low torque and must be used for low-speed applications. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

8. Hybrid is a Combination of VR and PM Motors • The hybrid step motor consists of two pieces of soft iron, as well as an axially magnetized, round permanent-magnet rotor. The term hybrid is derived from the fact that the motor is operated under the combined principles of the permanent magnet and variable-reluctance stepper motors. The stator core structure of a hybrid motor is essentially the same as its VR counterpart. The main difference is that in the VR motor, only one of the two coils of one phase is wound on one pole, while a typical hybrid motor will have coils of two different phases wound on one the same pole. The two coils at a pole are wound in a configuration known as abifilar connection. Each pole of a hybrid motor is covered with uniformly spaced teeth made of soft steel. The teeth on the two sections of each pole are misaligned with each other by a half-tooth pitch. Torque is created in the hybrid motor by the interaction of the magnetic field of the permanent magnet and the magnetic field produced by the stator. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

9. Step Rate • Stepper motors are rated in terms of the number of steps per second, the stepping angle, and load capacity in ounce-inches and the pound-inches of torque that the motor can overcome. The number of steps per second is also known as thestepping rate. The actual speed of a stepper motor is dependent on the step angle andstep rate and is found using the following equation: ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

10. Torque vs. Resolution • A plot of the relationship between pull-in torque versus pulses per second for a typical stepper motor. From this curve, it is apparent that torque is greatest at zero steps per second and decreases as the number of steps increases. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

11. Stepper Motor Drives • The direction of rotation is determined by applying the pulses to either the clockwise or counterclockwise drive circuits. Rotor displacement can be very accurately repeated with each succeeding pulse. Stepping motors are generally operated without feedback, which simplifies the control circuit considerably. One of the most common stepper motor drive circuits is thebipolar drive. This circuit uses bifilar windings and eight Darlington transistors to control the direction of rotation and the stepping rate of the motor. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

12. Stepper motor drivers are available in half-step or full-step configurations. Full-step drivers are the simplest in design and have a control sequence of two on-time periods followed by two off-time periods. The half-step mode of operation provides a smoother, quieter performance with higher speed capability and efficiency. The picture shows the switching sequence waveshapes of a typical stepper motor. Each stepper motor winding is energized one in every four input pulses. Consequently, the pulse train for each winding has a 25 percent duty cycle. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

13. Application Example ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

14. Peristalic Pumps • Peristaltic pumps provide hospitals and medical labs with accurate and repeatable pumping performance by the using microprocessor-controlled stepping motors with or without gearboxes. They are used to pump blood for heart-lung machines and kidney dialysis units. By varying the diameter of the tubing or the step rate of the motor, the pump volume and rate can be easily changed and controlled. Various fluids can be processed using the same pump by simply changing the tubes and reprogramming the pump parameters. Nothing but the tube touches the fluid, thus eliminating the risk of cross contamination between the pump and the fluid. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

15. More Applications ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

16. Stepper Motor Control • The indexer, or controller, provides step and direction outputs to the driver. Most applications require that the indexer manage other control functions as well, including acceleration, deceleration, steps per second and distance. The indexer can also interface to and control, many other external signals. • Integrated control means the indexer is embedded within the complete system and accepts commands from the host computer "on-line" throughout the entire motion process. Communication, operator interface and the I/O functions are designed as separate elements of the system. Control and management of the motion sequence is done by the host computer. In this case the indexer acts as an intelligent peripheral. CNC (computer numerical control) applications are well suited for integrated control because the data input is "dynamic", or changing frequently. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

17. Major Specifications • Holding torque is the maximum torque that the motor can produce with its shaft held firmly without movement, when the windings are energized. A motor's holding torque serves as a measure of relative merit in comparing one step motor with another. The relative value of a step motor can be judged by the torque delivered per unit volume. • Pull-in torque is the maximum torque a step motor can produce in a start-stop mode without stepping error. The torque produced depends greatly on the drive method. For this reason, the drive method should always be specified when calling out the pull-in torque—or, for that matter, any other type of torque. • Pull-out torque is the maximum torque a step motor can produce in a slewing mode, that is, without regard to starting and stopping. For any motor, the pull-out torque is always higher than the pull-in torque across the full range of speeds. • The pull-in (or start) speed range of a motor is its rotating-shaft speed range in pulses per second in a start-stop mode without step error. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

18. More Specifications • Slewing speed range is the rotating-shaft speed range of the motor expressed in pulses per second (PPS) without regard to starting and stopping. The speed in revolutions per minute (RPM) can be calculated from the PPS according to the formula PPS times 60 divided by the number of steps per revolution. For example, for a 1.8° hybrid step motor (200 steps per revolution), RPM = (PPS x 60)/200. • Rotor inertia is the property of the motor that signifies its ability to accelerate rapidly. It determines the torque needed to accelerate the motor to a specified speed within a specified time. The rotor inertia is often not negligible in comparison with the inertia of the load. It is therefore a very important specification in the load calculations. Commercial software that application engineers for good motor vendors can use is available to make the otherwise tedious load calculations easy. • Motor's maximum temperature limit If the motor is undersized for the application, it will get too warm and eventually burn up. Dialogue with the vendor's engineering department will ensure that load calculation is performed adequately and that the size of the motor chosen will be appropriate for the equipment. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

19. Stepping Motor Resolution and Step Angle • The resolution (number of steps) and step angle of a stepping motor is dependent on: • the number of rotor pole pairs • the number of motor phases • the drive mode (full or half step) The resolution can be calculated using the formula: • The step angle can then be calculated by dividing one rotation (360) by the number of steps. ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

20. Limitations • If speeds are more than 2000 rpm stepper may become bulky, also at high torque. • Use stepper motor if torque is lower than 500 oz-in, less than 2000 rpm, low to medium acceleration rates. • Preferred to be used in Open-Loop applications • Lose accuracy at high speeds ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

21. Choosing a Motor • Use a hybrid stepper motor if you are going to use a stepper motor • More torque than PM and VR stepper motors • Less acoustic noise • The only drawback is that hybrids cost more than PM and VR motors ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

22. When to Use a Stepper Motor • Positional accuracy is important • High torque and low speed applications • Low complexity is important • Open-loop control can be used • Easier to drive than servo motors ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

23. Selection Process ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

24. Cost Information • Actual prices for hybrid two-phase stepper motors at sanyo-denki online.com • The higher the required torque, the higher the price ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators

25. Where to get Hybrid Stepper Motors • Hurst Mfg.-www.myhurst.com/hurstmfg • Moons' Industries America, Inc.- http://www.moons.com.cn/english/index.htm • Oriental Motor U.S.A. Corp.- www.orientalmotor.com/products/ac/index.htm • Intelligent Motion Systems, Inc. -www.imshome.com/step_motors.htm • Danaher Motion/Pacific Scientific -www.danahermotion.com • Micromo Electronics, Inc.- www.micromo.com ECE5320 Mechatronics. Assignment#1 Survey on sensors and actuators