DOCSLIB.ORG

Stepper Motor Basics

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Stepper Motor Basics Industrial Circuits Application Note Stepper Motor Basics A stepper motor is an electromechanical Disadvantages device which converts electrical pulses into 15° discrete mechanical movements. The shaft 1. Resonances can occur if not A or spindle of a stepper motor rotates in properly controlled. D' discrete step increments when electrical 2. Not easy to operate at extremely B command pulses are applied to it in the high speeds. 1 proper sequence. The motors rotation has 6 several direct relationships to these applied 2 C' C input pulses. The sequence of the applied Open Loop Operation 5 pulses is directly related to the direction of One of the most significant advantages 3 motor shafts rotation. The speed of the of a stepper motor is its ability to be 4 B' motor shafts rotation is directly related to accurately controlled in an open loop D the frequency of the input pulses and the system. Open loop control means no length of rotation is directly related to the feedback information about position is A' number of input pulses applied. needed. This type of control eliminates the need for expensive Figure 1. Cross-section of a variable- sensing and feedback devices such as reluctance (VR) motor. Stepper Motor Advantages optical encoders. Your position is and Disadvantages known simply by keeping track of the input step pulses. Advantages 1. The rotation angle of the motor is Stepper Motor Types proportional to the input pulse. There are three basic stepper motor types. They are : 2. The motor has full torque at stand- N N S N S N still (if the windings are energized) • Variable-reluctance 3. Precise positioning and repeat- • Permanent-magnet ability of movement since good S N stepper motors have an accuracy of • Hybrid 3 – 5% of a step and this error is non cumulative from one step to Variable-reluctance (VR) S the next. This type of stepper motor has been 4. Excellent response to starting/ around for a long time. It is probably stopping/reversing. the easiest to understand from a structural point of view. Figure 1 Figure 2. Principle of a PM or tin-can 5. Very reliable since there are no con- shows a cross section of a typical V.R. stepper motor. tact brushes in the motor. stepper motor. This type of motor Therefore the life of the motor is consists of a soft iron multi-toothed simply dependant on the life of the rotor and a wound stator. When the S bearing. stator windings are energized with DC 6. The motors response to digital current the poles become magnetized. input pulses provides open-loop Rotation occurs when the rotor teeth N control, making the motor simpler are attracted to the energized stator N N and less costly to control. poles. 7. It is possible to achieve very low Permanent Magnet (PM) speed synchronous rotation with a Often referred to as a “tin can” or load that is directly coupled to the “canstock” motor the permanent S shaft. magnet step motor is a low cost and 8. A wide range of rotational speeds low resolution type motor with typical step angles of 7.5° to 15°. (48 – 24 Figure 3. Cross-section of a hybrid stepper can be realized as the speed is motor. proportional to the frequency of the steps/revolution) PM motors as the input pulses. 1 has some advantages such as very low in many different applications. Some inertia and a optimized magnetic flow of these include printers, plotters, path with no coupling between the highend office equipment, hard disk two stator windings. These qualities drives, medical equipment, fax are essential in some applications. N machines, automotive and many more. S N S N S N Size and Power The Rotating Magnetic Field In addition to being classified by their Figure 4. Principle of a disc magnet motor When a phase winding of a stepper step angle stepper motors are also developed by Portescap. motor is energized with current a classified according to frame sizes magnetic flux is developed in the name implies have permanent which correspond to the diameter of stator. The direction of this flux is magnets added to the motor structure. the body of the motor. For instance a determined by the “Right Hand The rotor no longer has teeth as with size 11 stepper motor has a body di- Rule” which states: the VR motor. Instead the rotor is ameter of approximately 1.1 inches. “If the coil is grasped in the right magnetized with alternating north Likewise a size 23 stepper motor has a hand with the fingers pointing in the and south poles situated in a straight body diameter of 2.3 inches (58 mm), direction of the current in the winding line parallel to the rotor shaft. These etc. The body length may however, (the thumb is extended at a 90° angle magnetized rotor poles provide an vary from motor to motor within the to the fingers), then the thumb will increased magnetic flux intensity and same frame size classification. As a point in the direction of the magnetic because of this the PM motor exhibits general rule the available torque out- field.” improved torque characteristics when put from a motor of a particular frame Figure 5 shows the magnetic flux compared with the VR type. size will increase with increased body path developed when phase B is ener- length. gized with winding current in the Hybrid (HB) Power levels for IC-driven stepper direction shown. The rotor then aligns The hybrid stepper motor is more motors typically range from below a itself so that the flux opposition is expensive than the PM stepper motor watt for very small motors up to 10 – minimized. In this case the motor but provides better performance with 20 watts for larger motors. The maxi- would rotate clockwise so that its respect to step resolution, torque and mum power dissipation level or south pole aligns with the north pole speed. Typical step angles for the HB thermal limits of the motor are seldom of the stator B at position 2 and its stepper motor range from 3.6° to 0.9° clearly stated in the motor manu- north pole aligns with the south pole (100 – 400 steps per revolution). The facturers data. To determine this we of stator B at position 6. To get the hybrid stepper motor combines the must apply the relationship P␣ =V ×␣I. motor to rotate we can now see that best features of both the PM and VR For example, a size 23 step motor may we must provide a sequence of type stepper motors. The rotor is be rated at 6V and 1A per phase. energizing the stator windings in such multi-toothed like the VR motor and Therefore, with two phases energized a fashion that provides a rotating contains an axially magnetized con- the motor has a rated power dissipa- magnetic flux field which the rotor centric magnet around its shaft. The tion of 12 watts. It is normal practice follows due to magnetic attraction. teeth on the rotor provide an even to rate a stepper motor at the power better path which helps guide the dissipation level where the motor case magnetic flux to preferred locations in rises 65°C above the ambient in still Torque Generation the airgap. This further increases the air. Therefore, if the motor can be The torque produced by a stepper detent, holding and dynamic torque mounted to a heatsink it is often motor depends on several factors. characteristics of the motor when com- possible to increase the allowable • The step rate pared with both the VR and PM power dissipation level. This is types. important as the motor is designed to • The drive current in the windings The two most commonly used types be and should be used at its maximum • The drive design or type of stepper motors are the permanent power dissipation ,to be efficient from magnet and the hybrid types. If a a size/output power/cost point of view. In a stepper motor a torque is devel- designer is not sure which type will oped when the magnetic fluxes of the best fit his applications requirements rotor and stator are displaced from he should first evaluate the PM type as When to Use a Stepper each other. The stator is made up of a it is normally several times less expen- Motor high permeability magnetic material. sive. If not then the hybrid motor may A stepper motor can be a good choice The presence of this high permeability be the right choice. whenever controlled movement is material causes the magnetic flux to required. They can be used to advan- be confined for the most part to the There also excist some special tage in applications where you need to paths defined by the stator structure stepper motor designs. One is the disc control rotation angle, speed, position in the same fashion that currents are magnet motor. Here the rotor is and synchronism. Because of the in- confined to the conductors of an elec- designed sa a disc with rare earth herent advantages listed previously, tronic circuit. This serves to concen- magnets, See fig. 5 . This motor type stepper motors have found their place trate the flux at the stator poles. The 2 torque output produced by the motor increase the number of steps per is proportional to the intensity of the revolution of the motor, or in other magnetic flux generated when the words to provide a smaller basic (full 8 1 winding is energized.
Load more

Recommended publications
  • Stepper Motor Or Servo Motor: Which Should It Be?
    Stepper Motor or Servo Motor: Which Should It Be? Engineer the Exceptional ENGINEER THE EXCEPTIONAL ENGINEER THE EXCEPTIONAL Stepper Motor or Servo Motor: Which Should It Be? Engineer the Exceptional ENGINEER THE EXCEPTIONAL Each technology has its niche, and since the selection of either stepper or servo ENGINEER THE EXCEPTIONAL technology affects the likelihood of success, it is important that the machine designer consider the technical advantages and disadvantages of both to select the best motor-drive system for an application. Machine designers should not limit utilization of steppers or servos This article presents an overview of stepper according to a fixed mindset or comfort level, but should learn where and servo capabilities to serve as selection each technology works best for controlling a specific mechanism and criteria between the two technologies. process to be performed. A thorough understanding of these technologies will help you achieve optimum Today’s digital stepper motor drives provide enhanced drive features, mechatronic designs to bring out the full option flexibility and communication protocols using advanced capabilities of your machine. integrated circuits and simplified programming techniques. The same is true of servo motor systems, while higher torque density, improved electronics, advanced algorithms and higher feedback resolution have resulted in higher system bandwidth capabilities as well as lower initial and overall operating costs for many applications. STEPPER MOTOR SYSTEM OVERVIEW Stepper motors have several major advantages over servo systems. They typically cost less, have common NEMA mountings, offer lower-torque options, require less-costly cabling, and their open-loop motion control simplifies machine integration and operation.
    [Show full text]
  • Stepping Motors Fundamentals
    AN907 Stepping Motors Fundamentals Author: Reston Condit TYPES OF STEPPING MOTORS Microchip Technology Inc. There are three basic types of stepping motors: Dr. Douglas W. Jones permanent magnet, variable reluctance and hybrid. University of Iowa This application note covers all three types. Permanent magnet motors have a magnetized rotor, while variable reluctance motors have toothed soft-iron rotors. Hybrid INTRODUCTION stepping motors combine aspects of both permanent Stepping motors fill a unique niche in the motor control magnet and variable reluctance technology. world. These motors are commonly used in measure- The stator, or stationary part of the stepping motor ment and control applications. Sample applications holds multiple windings. The arrangement of these include ink jet printers, CNC machines and volumetric windings is the primary factor that distinguishes pumps. Several features common to all stepper motors different types of stepping motors from an electrical make them ideally suited for these types of point of view. From the electrical and control system applications. These features are as follows: perspective, variable reluctance motors are distant 1. Brushless – Stepper motors are brushless. The from the other types. Both permanent magnet and commutator and brushes of conventional hybrid motors may be wound using either unipolar motors are some of the most failure-prone windings, bipolar windings or bifilar windings. Each of components, and they create electrical arcs that these is described in the sections below. are undesirable or dangerous in some environments. Variable Reluctance Motors 2. Load Independent – Stepper motors will turn at Variable Reluctance Motors (also called variable a set speed regardless of load as long as the switched reluctance motors) have three to five load does not exceed the torque rating for the windings connected to a common terminal.
    [Show full text]
  • Difference Between Bipolar Drives and Unipolar Drives for Stepper Motors
    WHITE PAPER DIFFERENCE BETWEEN BIPOLAR DRIVES AND UNIPOLAR DRIVES FOR STEPPER MOTORS orking on a motorized development requires some knowledge about motors and controllers. This article Wis focused on the stepper motors which is a type of brushless DC motor with a high number of poles. This technology is generally driven in open loop without any feedback sensor, meaning the current is typically applied on the phases without knowing the rotor position. The rotor moves to be aligned with the stator magnetic flux, then the current can be supplied to the next phase. We will consider two ways to supply current in the coil: bipolar way and unipolar way. In this article, we will explain the differences of bipolar and unipolar motors and driving methods. We will show the advantages and limits of both technologies. Let’s take an example of a four step, permanent magnet stepper motor (see figure 1). The rotor is made with a one pole pair magnet, and the stator is composed of two phases, Phase A and Phase B. • In unipolar: the current always flows in the same direction. Each coil is dedicated to one current direction, meaning either the coil A+ or the coil A- is powered. The coils A+ and A- are never powered together. • In bipolar: the current can flow in both directions in all coils. The phases A+ and A- are powered together. A bipolar motor requires one coil minimum per phase and unipolar motor Figure 1. 4-Step Stepper Motor requires two coils minimum per phase. Let’s review both options in more detail.
    [Show full text]
  • Motor Actuators Basics
    Motor Actuators Basics - 1 - Note: All specifications and other information are not guaranteed and are subject to change without notice. Prior to any new usage of JE motor actuators it is recommended to contact Johnson Electric. All information below and content of links are subject to the disclaimer of the Johnson Electric website - 2 - Contents Overview ....................................................................................................................................................................... 4 Classification ............................................................................................................................................................. 5 DC Motors ................................................................................................................................................................. 6 Universal Motors ....................................................................................................................................................... 7 BLDC Motors ............................................................................................................................................................. 8 Synchronous Motors ................................................................................................................................................. 9 Stepper Motors ........................................................................................................................................................ 10 Shaded
    [Show full text]
  • Stepper Motor
    STEPPER MOTOR Stepper motors are used in a wide variety of applications, including computer peripherals like printers, scanners, CD drives, camera lenses, etc. In this first article, in a series of articles on stepper motors, we will introduce the reader to the theory behind the working and control of a stepper motor. Stepper Motor Basics A Stepper Motor just like any other motor, converts electrical energy into mechanical energy. A stepper motor consists of the following parts: Stator The stationary part of the motor. In a stepper motor, the stator is a set of electromagnets. Rotor The non-stationary part of the motor. In a stepper motor, the rotor is a permanent magnet. The arrangement of the electromagnets and the permanent magnets in a simple stepper motor is shown in the following diagram. Stepper Motor Construction Stepper Motor Operation Stepper Motor Operation When each of the electromagnet pairs is energized successively, the permanent magnet is attracted to the electromagnet, and aligns with it. This results in rotation of the permanent magnet. This is illustrated in “Stepper Motor Operation” diagram. The stepper motor gets its name from the fact that the rotor rotates in discrete step increments. The simple stepper motor has a step angle of 90 degrees. More complex stepper motors can have step angles as low as 3.6 degrees. These stepper motors have more no. of poles in the rotor. A complex stepper motor is shown in below diagram. The dark grey areas on the rotor are South poles and light grey areas on the rotor are North poles.
    [Show full text]
  • Stepper Motors
    Stepper Motors By Brian Tomiuk, Jack Good, Matthew Edwards, Isaac Snellgrove November 14th, 2018 1 What is a Stepper Motor? ● A motor whose movement is divided into discrete “steps” ○ “Turn 10 steps clockwise” ● Holds its position without additional control ○ No sensor or feedback loop 2 Parts of a Stepper Motor Stator - Stays Static Rotor - Rotates the motor shaft https://phidgets.files.wordpress.com/2014/06/stepper_back_web.jpg 3 Different Types of Torque Holding torque - How much load can the motor hold in place when the coils are energized Detent torque - The torque the motor produces when the windings are not energized, sometimes call residual torque 4 Advantages of Stepper Motors ● Has high holding torque (maintains its position) ● Moves in discrete amounts ● Inexpensive ● Brushless (can last longer than brushed motors) 5 Disadvantages of Stepper Motors ● Uses the same amount of power regardless of load ○ Lower power efficiency ● Torque decreases rapidly as speed increases ● No internal feedback ○ Cannot tell when a step was missed ○ Must step slowly to ensure accuracy ● Low torque to inertia ○ Cannot accelerate loads very rapidly 6 How Stepper Motors Work 7 How a Stepper Motor Works Unpowered Electromagnets Bar with magnetic ends A basic stepper motor consists of a series of electromagnets surrounding a magnetically charged bar 8 How a Stepper Motor Works S Powering a pair of the electromagnets causes the middle bar to align with the electromagnets S 9 How a Stepper Motor Works Changing which electromagnets are powered and unpowered
    [Show full text]
  • Piezoelectric Inertia Motors—A Critical Review of History, Concepts, Design, Applications, and Perspectives
    Review Piezoelectric Inertia Motors—A Critical Review of History, Concepts, Design, Applications, and Perspectives Matthias Hunstig Grube 14, 33098 Paderborn, Germany; [email protected] Academic Editor: Delbert Tesar Received: 26 November 2016; Accepted: 18 January 2017; Published: 6 February 2017 Abstract: Piezoelectric inertia motors—also known as stick-slip motors or (smooth) impact drives—use the inertia of a body to drive it in small steps by means of an uninterrupted friction contact. In addition to the typical advantages of piezoelectric motors, they are especially suited for miniaturisation due to their simple structure and inherent fine-positioning capability. Originally developed for positioning in microscopy in the 1980s, they have nowadays also found application in mass-produced consumer goods. Recent research results are likely to enable more applications of piezoelectric inertia motors in the future. This contribution gives a critical overview of their historical development, functional principles, and related terminology. The most relevant aspects regarding their design—i.e., friction contact, solid state actuator, and electrical excitation—are discussed, including aspects of control and simulation. The article closes with an outlook on possible future developments and research perspectives. Keywords: inertia motor; stick-slip motor; smooth impact drive; piezeoelectric motor; review 1. Introduction Piezoelectric actuators have long been used in diverse applications, especially because of their short response time and high resolution. The major drawback of these solid state actuators in positioning applications is their small stroke: actuators made of state-of-the-art lead zirconate titanate (PZT) ceramics only reach strains up to 2 . A typical piezoelectric actuator with 10 mm length thus reaches a maximum stroke of only 20 µm.h Bending actuator designs [1] and other mechanisms [2] can increase the stroke at the expense of stiffness and actuation force ([3]; [4] (pp.
    [Show full text]
  • Simple Torque Control Method for Hybrid Stepper Motors Implemented in FPGA
    electronics Article Simple Torque Control Method for Hybrid Stepper Motors Implemented in FPGA Stefano Ricci * and Valentino Meacci Information Engineering Department (DINFO), University of Florence, 50139 Florence, Italy; valentino.meacci@unifi.it * Correspondence: stefano.ricci@unifi.it; Tel.: +39-0552758585 Received: 12 September 2018; Accepted: 4 October 2018; Published: 7 October 2018 Abstract: Stepper motors are employed in a wide range of consumer and industrial applications. Their use is simple: a digital device generates pulse-bursts and a direction bit towards a power driver that produces the 2-phase currents feeding the motor windings. Despite its simplicity, this open-loop approach fails if the torque load exceeds the motor capacity, so the motor and driver should be oversized at the expense of efficiency and cost. Field-Oriented closed-loop Control (FOC) solves the problem, and the recent availability of low cost electronics devices like Digital Signal Processors, Field Programmable Gate Arrays (FPGA), or even Microcontrollers with dedicated peripherals, fostered the investigation and implementation of several variants of the FOC method. In this paper, a simple and economic FOC torque control method for hybrid stepper motors is presented. The load angle is corrected accordingly to the actual shaft position through pulse-bursts and direction commands issued towards a commercial stepper driver, which manages the 2-phase winding currents. Thanks to the FPGA implementation, the control loop updates the electrical position every 50 µs only, thus allowing a load angle accuracy of −1/100 rad for a rotor velocity up to 750 rev/min, as shown in the reported experiments. Keywords: stepper motor; torque control; closed-loop control; Field Programmable Gate Array (FPGA) 1.
    [Show full text]
  • Electrical Engineering
    DEPARTMENT OF ELECTRICAL ENGINEERING Syllabus for M. Tech. Power Electronics & Drives MEE-101 Advance Microprocessors and Applications Max. Marks: 100 (Credit=5) L T P 3 1 2 UNIT I (9 Lecture) Introduction to Microprocessors and Microcontrollers: Review of basics microprocessor,architecture and instruction set of a typical 8-bit microprocessor.Overview of 16 bit and 32 bit microprocessors, arithmetic and I/O coprocessors. Architecture, register details, operation, addressing modes and instruction set of 16 bit 8086 microprocessor, assembly language programming, introduction to multiprocessing, multi-user, multitasking operating system concepts, Pentium-1,2,3 and 4 processors, Motorola 68000 processor.Concepts of micro controller and microcomputer, microcontroller (8051/8751) based design, applications of microcomputer in on line real time control UNIT II (9 Lecture) Input/Output,Memory Interfacing: Parallel and series I/O, Interrupt driven I/O, single and multi-interrupt levels, use of software polling and interrupt controlling for multiplying interrupt levels, programmable interrupt controller, DMA controller, programmable timer/counter, programmable communication and peripheral interface, synchronous and asynchronous data transfer, standard serial interfaces like Rs.232. Types of Memory, RAM and ROM interfacing with timing considerations, DRAM interfacing UNIT III (9 Lecture) Programmable Support Chips: Functional schematic, operating modes, programming and interfacing of 8255, 8251, 8259 and 8253 with microprocessor UNIT IV (9 Lecture) Analog Input & Output: Microprocessor compatible ADC and DAC chips, interfacing of ADC and DAC with microprocessor, user of sample and hold circuit and multiplexer with ADC. Microprocessor Applications: Design methodology, examples of microprocessor applications. Lists of experiments 1. Simple arithmetic operations: Multi precision addition / subtraction / multiplication / division.
    [Show full text]
  • Motor Actuators Basics
    Motor Actuators Basics - 1 - Note: All specifications and other information are not guaranteed and are subject to change without notice. Prior to any new usage of JE motor actuators it is recommended to contact Johnson Electric. All information below and content of links are subject to the disclaimer of the Johnson Electric website - 2 - Contents Overview ....................................................................................................................................................................... 4 Classification ............................................................................................................................................................. 5 DC Motors ................................................................................................................................................................. 6 Universal Motors ....................................................................................................................................................... 7 BLDC Motors ............................................................................................................................................................. 8 Synchronous Motors ................................................................................................................................................. 9 Stepper Motors ........................................................................................................................................................ 10 Shaded
    [Show full text]
  • Simple Discussion on Stepper Motors for the Development of Electronic
    International Journal of Scientific & Engineering Research, Volume 5, Issue 1, January-2014 1089 ISSN 2229-5518 Simple Discussion on Stepper Motors for the Development of Electronic Device Tanu Shree Roy, Humayun Kabir, Md A. Mannan Chowdhury Abstract— This paper is designed and developed to have the general as well as basic knowledge about the modern electronic device named ‘Stepper motor’. A step motor can be viewed as a synchronous AC motor with the number of poles (on both rotor and stator) in- creased, taking care that they have no common denominator. Additionally, we have discussed about its characteristics, classification, oper- ation, advantages and electric magnetic effects. Index Terms— Electronic device, stepper motor, synchronous, rotor, stator, electric and magnetic effects. —————————— —————————— 1 INTRODUCTION Stepper motors can be viewed as electric motors without trol. Stepper systems are economical to implement, intuitive to commentators. Typically all windings in the motor are part control, and have good low speed torque, making them ideal of the stator and the rotor is permanent magnet or in the case for many low power, computer-controlled applications. They of variable reluctance motors, a toothed block of some magneti- can be for example interfaced to computer using few transistors cally soft material. All of the commutation must be handled and made to rotate using a small piece of software. Stepper mo- externally by the motor controller, and typically, the motors and tors provide good position repeatability. Stepper motors are controllers are designed so that the motor may be held in any used in robotics control and in computer accessories (disk fixed position as well as being rotated one way or the other [1, drives, printers, scanners etc.).
    [Show full text]
  • Introduction to Stepper Motors Part 1: Types of Stepper Motors
    Introduction to Stepper Motors Part 1: Types of Stepper Motors © 2007 Microchip Technology Incorporated. All Rights Reserved. Introduction to Stepper Motors Slide 1 Hello, my name is Marc McComb, I am a Technical Training Engineer here at Microchip Technology in the Security, Microcontroller and Technology Division. Thank you for downloading Introduction to Stepper Motors. This is Part 1 in a series of webseminars related to Stepper Motor Fundamentals. The following webseminar will focus on some of the stepper motors available for your applications. So let’s begin. 1 Agenda z Topics discussed in this WebSeminar: − Main components of a stepper motor − How do these components work together − Types of stepper motors © 2007 Microchip Technology Incorporated. All Rights Reserved. Introduction to Stepper Motors Slide 2 During this webseminar I will discuss the main components of a stepper motor and how these components work together to actually turn the rotor. We will also explore three types of stepping motors as well as two sub categories. 2 Stepper Motor Basics © 2007 Microchip Technology Incorporated. All Rights Reserved. Introduction to Stepper Motors Slide 3 So let’s start off with some stepper motor basics 3 What is a Stepper Motor? z Motor that moves one step at a time − A digital version of an electric motor − Each step is defined by a Step Angle Start Position Step 1 Step 2 © 2007 Microchip Technology Incorporated. All Rights Reserved. Introduction to Stepper Motors Slide 4 First, what is a stepper motor? As the name implies, the stepper motor moves in distinct steps during its rotation. Each of these steps is defined by a Step Angle.
    [Show full text]