er. bhushan kumar weaving executive raymond textiles ltd vapi, gujarat, india erbhushan@2015 ...
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Er . Bhushan KumarWeaving Executive
Raymond Textiles LtdVapi, Gujarat, India
erbhushan@2015
www.er-bhushan.in
Switched Reluctance Motor Principle
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Switched Reluctance Motor Principle
The switched reluctance motor (SRM) is a type of a stepper motor, an electric motor that runs by reluctance torque
The SRM has wound field coils for the stator windings. The rotor has no magnets or coils attached. It is a solid salient-pole rotor (having projecting magnetic poles) made of soft magnetic material (often laminated-steel).
When power is applied to the stator windings, the rotor's magnetic reluctance creates a force that attempts to align the rotor pole with the nearest stator pole.
In order to maintain rotation, an electronic control system switches on the windings of successive stator poles in sequence so that the magnetic field of the stator "leads" the rotor pole, pulling it forward
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Simple Switching…….
If the poles A0 and A1 are energized then the rotor will align itself with these poles. Once this has occurred it is possible for the stator poles to be de-energized before the stator poles of B0 and B1 are energized. The rotor is now positioned at the stator poles B. This sequence continues through C before arriving back at the start. This sequence can also be reversed to achieve motion in the opposite direction. This sequence can be found to be unstable[ while in operation, under high load, or high acceleration or deceleration, a step can be missed, and the rotor jumps to wrong angle, perhaps going back one instead of forward three.
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Improved Sequence…….
A much more stable system can be found by using the following “Quadrature" sequence. First, stator poles A0 and A1 are energized. Then stator poles of B0 and B1 are energized which pulls the rotor so that it is aligned in between the stator poles of A and B. Following this the stator poles of A are de-energized and the rotor continues on to be aligned with the stator poles of B, this sequence continues through BC, C and CA before a full rotation has occurred. This sequence can also be reversed to achieve motion in the opposite direction. As at any time two coils are energized, and there are more steps between positions with identical magnetization, so the onset of missed steps occurs at higher speeds or loads.
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Stepper Motor…….
The switched reluctance motor (SRM) is a type of a stepper motor, an electric motor that runs by reluctance torque
The radial movement is carried out by 4 double stator coils. The main motor contains 4 n double stator coils, which are controlled by the PB---board in the power control box of the main motor.
The stepper motor does not rotate in a continuous fashion like a conventional DC motor but moves in discrete “Steps” or “Increments”, with the angle of each rotational movement or step dependant upon the number of stator poles and rotor teeth the stepper motor has.
Because of their discrete step operation, stepper motors can easily be rotated a finite fraction of a rotation at a time, such as 1.8, 3.6, 7.5 degrees etc. So for example, lets assume that a stepper motor completes one full revolution 360o in exactly 100 steps.Then the step angle for the motor is given as 360 degrees/100 steps = 3.6 degrees per step. This value is commonly known as the stepper motors Step Angle.
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Stepper Motor…….
There are three basic types of stepper motor, Variable Reluctance, Permanent Magnet and Hybrid (a sort of combination of both). A Stepper Motor is particularly well suited to applications that require accurate positioning and repeatability with a fast response to starting, stopping, reversing and speed control and another key feature of the stepper motor, is its ability to hold the load steady once the require position is achieved.
Generally, stepper motors have an internal rotor with a large number of permanent magnet “teeth” with a number of electromagnet “teeth” mounted on to the stator. The stators electromagnets are polarized and depolarized sequentially, causing the rotor to rotate one “step” at a time.
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Stepper Motor…….
simple example of a variable reluctance stepper motor, the motor consists of a central rotor surrounded by four electromagnetic field coils labelled A, B, C and D. All the coils with the same letter are connected together so that energizing, say coils marked A will cause the magnetic rotor to align itself with that set of coils.By applying power to each set of coils in turn the rotor can be made to rotate or "step" from one position to the next by an angle determined by its step angle construction, and by energizing the coils in sequence the rotor will produce a rotary motion.
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Stepper Motor…….
The stepper motor driver controls both the step angle and speed of the motor by energizing the field coils in a set sequence for example, “ADCB, ADCB, ADCB, A…” etc, the rotor will rotate in one direction (forward) and by reversing the pulse sequence to “ABCD, ABCD, ABCD, A…” etc, the rotor will rotate in the opposite direction (reverse).
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Stepper Motor Driver
A stepper motor drive is a circuit which is used to drive or run a stepper motor. It is often called a stepper motor driver. A stepper motor drive usually consists of a controller, a driver and the connections to the motor.
Essential Components of Stepper Motor Drive1) Controller(Essentially a microprocessor) 2) A driver IC to handle the motor current 3) A power supply unit
Miscellaneous Components4) Switches, Potentiometers 5) Heat sink 6) Connecting wires
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Stepper Motor Driver
PICANOL DDMP-4 board BE214832 (hardware for sumo motor control)
Most recently, a Data-Driven Media Processor (DDMP) has been designedat Sharp capable of 2400 million signal processing operations per second while consuming only 1.32 W.
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Stepper Motor Driver
The steps of a stepper motor represent discrete angular movements, that take place in a successive fashion and are equal in displacement, when functioning correctly the number of steps performed must be equal to the control impulses applied to the phases of the motor. The final position of the rotor is given by the total angular displacement resulting from the number of steps performed
This position is kept until a new impulse, or sequence of impulses, is applied. These properties make the stepper motor an excellent execution element of open-loop control systems. A stepper motor does not lose steps, i.e. no slippage occurs, it remains synchronous to control impulses even from standstill or when braked, thanks to this characteristic a stepper motor can be started, stopped or reversed in a sudden fashion without losing steps throughout its operation.
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Stepper Motor Driver
Speed of a stepper motor can be controlled in a broad range of values by altering the frequency of input impulses. For example if the angular displacement per step is 1.8 degrees, the number of total impulses required for a complete revolution is 200, so for an input frequency of 400 impulses per second the speed of the motor is 120 rpm. Stepper motors can operate with input frequencies up to 2000 impulses (steps) per second, with step values from 0.3 to 180 degrees.
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Specific Stepper Motor Parameters
Step angle – represents angular displacement of the rotor for one control impulse;Maximum no load start frequency – represents the maximum control impulse frequency at which the unloaded motor can start, stop or reverse without losing steps;Limit start frequency – represents the maximum impulse frequency at which the motor can start without losing steps, when a given moment of inertia and torque load are presented at the shaft;Pull-in torque – represents maximum torque load at the shaft, at which the motor can start without losing steps;Maximum no load frequency – represents the maximum impulse frequency that the motor can follow without losing synchronization;Maximum frequency – maximum frequency of impulses at which a motor keeps its timing for given torque load and inertia;Pull-out torque – maximum torque that can be maintained by the motor at a certain speed, without losing steps;Angular speed – is calculated as a product between the stepping angle and the control frequency;Detent torque – represents the value of the holding torque presented by at the motor shaft when it is not electrically energized.
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Stepper Motor
The command to the pulse generator sets the number of steps for rotation and direction of rotation. The pulse generator correspondingly generates a train of pulse. The Translator is a simple logical device and distributes the position pulse train to the different phases. The amplifier block amplifies this signal and drives current in the corresponding winding. The direction of rotation can also be reversed by sending a direction pulse train to the translator. After receiving a directional pulse the step motor reverses the direction of rotation.
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