STEPPING MOTORS A GUIDE TO THEORY AND PRACTICE PDF
Stepping motors: a guide to theory and practice flux lines airgap magnetically permeable material forces t n forces t n. Figure Force components between two. INTRODUCTION. Stepping motors fill a unique niche in the motor control In practice, these motors typically have . provide a path which helps guide the magnetic flux to preferred Notes, (myavr.info pdf). This tutorial covers the basic principles of stepping motors and stepping motor control systems, Stepping motors: a guide to modern theory and practice.
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Description. Scope: Stepping motor technology is well established and used for motion control, most notably for computer peripherals but also wherever digital. Buy e-book PDF. $ (plus tax if applicable). Add to cart. Buy print edition. image of Stepping Motors: a guide to theory and practice. Author(s): Paul Acarnley. PDF | This paper describes the open-loop control of a stepper motors. Bipolar stepper Stepping Motors: a Guide to Modern Theory and Practice, 3 rd Edition.
But in all these machines, the rotors of their motors spin continuously. When you vacuum a carpet or commute to work by subway, the motors that are working for you turn around an arbitrary number of times: there's no precise control over how many times they rotate and what angle they spin through—and it really doesn't matter. Photo: Motor mouth: This "emotional" robot has a face that can show different expressions. The various parts are operated by stepper motors, precisely controlled by electronic circuits.
Now suppose you want to make an electric-powered robot arm that turns through an exact angle an exact number of degrees so it can successfully grab a cup of coffee off your desk. You could fit an electric motor onto a wooden or plastic lever to make it turn when you switch on the power, and you could flick the power on very briefly so the arm sweeps through a certain angle and then stops.
The trouble is, there's no way of knowing how much of an angle the motor or the arm will move: it depends on everything from the power of the motor and the electric current driving it to the weight of the arm and even which way the wind is blowing.
A motor that moves in such an arbitrary way is no use whatever in robotics: your coffee will surely end up on the floor! That's where a stepper motor comes in: it's a special kind of DC motor designed so you can make it rotate through a precise angle, instead of spinning round by a random amount. What exactly is a stepper motor?
Photo: The philosophy of steps: we think of steps as a way to climb up, but they're also a way to break a fixed distance into equal-sized pieces so we get more control over our movements. We can think of them as turning vague, variable, analog amounts of distance into specific, discrete, digital chunks.
Stepper motors are different from ordinary DC motors in at least four important ways. The first difference you notice is that they have no brushes or commutator the parts of a DC motor that reverse the electrical current and keep the rotor—the rotating part of a motor—constantly turning in the same direction. In other words, stepper motors are examples of what we call brushless motors. You'll also find brushless motors in many electric vehicles, hidden away in the wheel hubs; used in that way, they're called hub motors.
The second major difference is in what rotates.
Remember that in a basic DC motor, there is an outer permanent magnet or magnets that stays static, known as the stator, and an inner coil or coils of wire that rotates inside it, which is the rotor.
In a brushless hub-motor, the coils of wire are static in the center and the permanent magnets spin around them on the outside. A stepper motor is different again. This time, the permanent magnets are on the inside and rotate making up the rotor , while the coils are on the outside and stay static making up the stator.
The third big difference between an ordinary DC motor and a stepper motor is in the design of the stator and the rotor. Instead of one large magnet on the outside the stator and one large coil rotating inside it the rotor , a stepper motor has an inner magnet effectively divided up into many separate sections, which look like teeth on a gear wheel.
The outer coils have corresponding teeth that provide magnetic impulses, attracting, repelling, and making the teeth of the inner wheel rotate by small steps. This will become clear in a moment when we look at some pictures.
The final difference is that a stepper motor can stay still, in a certain position, once it's rotated through a particular angle. That's obviously crucially important if you want a motor to power something like a robot arm, which might have to rotate a certain amount and then remain in precisely that spot while another part of the robot does something else. This feature is sometimes called holding torque torque is the rotary force something has, so "holding torque" simply means a stepping motor's ability to stay still.
How does a stepper motor work? The basic construction I'm going to simplify stepper motors here to illustrate the simple, central idea: the inside rotor of a stepper motor turns by small, discrete amounts steps because the outside stator applies magnetic impulses that pull and push it around.
Photo: A stepper motor's rotor is made from two discs placed together so we get a series of alternating north and south poles. I've simulated the idea by coloring my hands and putting them on top of one another so the fingers alternate when viewed from above.
The rotor The rotor itself is made from two discs, a little like gears, one of which is a magnetic north pole red and the other is a south pole blue. When we put the two discs back to back, we get north and south pole teeth alternating around the edge. If you find that hard to picture, imagine your left hand is a magnetic north pole and is colored red, while your right hand is a magnetic south pole and colored blue. If you put one hand on top of the other so the fingers of one hand alternate with the fingers of the other, then look down, you'll see alternating north and south pole "teeth" the fingers around the edge.
That's effectively what we have in the rotor of a stepper motor. The stator Around the edge of the rotor, we have the stator: in this example, four electromagnets that can be switched on and off individually.
E-mail address: alexandru. Published by Elsevier Ltd. These motors are commonly used in measurement and control applications, such as positioning systems for NC machines, ink jet printers, robotics, computer peripherals, automotive devices and small business machinesfl, 2]. Although stepper motor are known for a long time, they have achieved their wide popularity in the last thirty years due to development of electronics which enables construction of cheap and reliable control circuits capable to satisfy complex requirements regarding motor torque, speed and angular displacement.
Advantages of stepper motors are: low costs, small dimensions, possibility to transform the pulses from digital inputs into angular movement-step, number of steps is equal to the number of control pulses. Hybrid stepper motor construction and principle of operation Hybrid stepper motors have magnetic core which is excited by combination of electrical windings and permanent magnet.
Images at the hybrid stepper motor is shown in Fig. Images at the hybrid stepper motor.
The hybrid stepper motor combine features of both the variable reluctance stepper and the permanent magnet stepper to produce a smaller step angle[3,5]. The rotor is a cylindrical permanent magnet, magnetized along the axis with radial soft iron teeth , shown in Fig.
The stator coils are wound on alternating poles with corresponding teeth. There are typically two winding phases distributed between pole pairs. This winding may be center tapped for unipolar drive.
The center tap is achieved by a bifilar winding, a pair of wires wound physically in paralel, but wired in series. The north-south poles of a phase swap polarity when the phase drive current is reversed. Bipolar drive is required for un-tapped windings. Note that the 50 -teeth on one rotor section are offset by half a pitch from the other.
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See rotor pole detail above. This rotor tooth offset is also shown below. Due to this offset, the rotor effectively has interleaved poles of opposite polarity. Two phase windings are common as shown above and below. The stator teeth on the 8-poles correspond to the 50 -rotor teeth, except for missing teeth in the space between the poles.
Thus, one poleof the rotor, say the south pole, may align with the stator in 50 distinct positions. However, the teeth of the south pole are offset from the north teeth by half a tooth. Therefore, the rotor may align with the stator in distinct positions.
This half tooth offset shows in the rotor pole detail above. These stator phases are offset from one another by one-quarter of a tooth. This detail is only discernible on the schematic diagrams below.
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Construction of hybrid stepper motor. The result is that the rotor moves in steps of a quarter of a tooth when the phases are alternately energized. The above drawing is representative of an actual hybrid stepper motor. However, we provide a simplified pictorial and schematic representation, shown in Fig. Total inertia Total inertia momentum, J, in kg.
Total viscous friction coefficient Total viscous friction coefficient, B, in N.
What exactly is a stepper motor?
Default is 1e Sample time -1 for inherited Specify the stepper motor sample time, in s. Specify —1 to inherit the sample time of the powergui block in your model. Default is —1. Variable Reluctance Select Variable reluctance to implement a variable-reluctance stepper motor.Step angle Step angle, in degrees, of the rotor movement. This rotor tooth offset is also shown below. Here's the filed design officially patented on March 7, , titled "Art of producing step-by-step movements," which uses an outer ring of five magnets energized in various combinations to make a pair of inner magnets and a shaft rotate.
One of the big difficulties of making well-behaved robots is that simple electric motors are impossible to move precisely. Oscillation, Instability and Control of Stepper Motors. We can make it rotate the opposite way by reversing the electric current. This time, the permanent magnets are on the inside and rotate making up the rotor , while the coils are on the outside and stay static making up the stator.