Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)


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The standard definition for an AC Motor is an electric motor that is driven by alternating current. The AC Motor is used in the conversion of electrical energy into mechanical energy. This mechanical energy is made from utilizing the force that is exerted by the rotating magnetic fields produced by the alternating current that flows through its coils. The AC Motor is made up of two major components: The fundamental operation of an AC Motor relies on the principles of magnetism. The simple AC Motor contains a coil of wire and two fixed magnets surrounding a shaft.

Stepping Motors: A Guide to Theory and Practice - Paul Acarnley - Google Книги

When an electric AC charge is applied to the coil of wire, it becomes an electromagnet, generating a magnetic field. Simply described, when the magnets interact, the shaft and the coil of wires begin to rotate, operating the motor. AC Motor products have two options for feedback controls. While both the AC Motor resolver and AC Motor encoder offer the same solution in multiple applications, they are greatly different. AC Motor resolvers use a second set of stator coils called the transformer to provoke rotor voltages across an air gap.

Since the resolver lacks electronic components, it is very rugged and operates over a large temperature range. The AC Motor resolver is also naturally shock resistant, due to how it is designed. The resolver is often used in harsh environments. The AC Motor optical encoder uses a shutter that rotates to disrupt a beam of light that crosses the air gap between a light source and the photo detector.

The rotating of the shutter over time causes wear on the encoder. This wear reduces the durability and dependably of the optical encoder. The type of application will establish whether a resolver or an encoder is desired. AC Motor encoders are easier to implement and more precise, so they should be the primary preference for any application. A resolver should only be chosen if the environment in which it will be used requires it.

These AC Motor types are determined by the rotor design used in the construction. Anaheim Automation carries all three types in its product line.

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Induction AC Motors are referred to as asynchronous motors or rotating transformers. This type of AC Motor uses electromagnetic induction to power the rotating device which is usually the shaft. The rotor in Induction AC Motor products typically turns slower than the frequency that is supplied to it. Induced current is what causes the magnetic field that envelops the rotor of these motors. This Induction AC Motor is designed in one or three phases.

Synchronous AC Motor The Synchronous Motor is typically an AC Motor that has its rotor spinning at the same rate as the alternating current that is being supplied to it. The rotor can also turn at a sub multiple of the current it is supplied. Slip rings or a permanent magnet supplied with current is what generates the magnetic field around the rotor. AC Industrial Motors are designed for applications requiring a three-phase, high-power induction motor.

The power ratings of an industrial motor exceed those of a standard single-phase AC induction motor. What Industries are AC Motors used in?

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AC Motors are primarily used in domestic applications due to their relatively low manufacturing costs, and durability, but are also widely used in industrial applications. What Applications are AC Motors used for? AC Motors can be found in numerous home appliances and applications, including: How are AC Motors Controlled? An AC Controller can also be referred to as a variable frequency drive , adjustable speed drive , frequency converter, etc.

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This adjustable output allows the motor speed to be precisely controlled. The inverter can also be used to control output current flow if needed. Both the rectifier and inverter are directed by a set of controls to generate a specific amount of AC voltage and frequency to match the AC motor system at a given point in time. Applications An AC Controller can be used in many different industrial and commercial applications.

Most often used to control fans in air conditioning and heating systems, the AC Controller allows for more control of the airflow. The AC Controller also aids in adjusting the speed of pumps and blowers. More recent applications include conveyors, cranes and hoists, machine tools, extruders, film lines, and textile-fiber spinning machines. Advantages - Increases the life of the motor due to high power factor - Economical speed control - Optimize motor-starting characteristics - Lower maintenance than DC control. Disadvantages - Generates a large amount of heat and harmonics.

However, AC speed control was a challenging task. When precise speed control was required, the DC motor became a replacement for the AC motor, because of its efficient and economical means of controlling speed accurately. It wasn't until the 's that AC speed control became a competitor. Over time, AC Drive technology eventually transformed into an inexpensive and reliable competitor to the traditional DC control. Now, an AC Controller is capable of speed control with full torque attained from 0 RPM through the maximum rated speed.

Basics The Variable Frequency Drive is a particular kind of adjustable-speed drive that is used to control the speed of an AC motor. In order to control the motor's rotational speed, a Variable Frequency Drive controls the frequency of the electrical power supplied to it. Adding a Variable Frequency Drive to an application allows the motor speed to be adjusted in accordance with the motor's load, ultimately saving energy.

Commonly used in a myriad of applications, a Variable Frequency Drive can be found operating ventilation systems, pumps, conveyors and machine tool drives. How a Variable Frequency Drive Works When complete voltage is applied to an AC motor, it accelerates the load and drops torque initially, keeping current especially high until the motor reaches full speed.


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A Variable Frequency Drive operates differently; it eliminates excessive current, increasing voltage and frequency in a controlled manner as the motor starts. A Variable Frequency Drive converts power through three different stages. First, AC power is converted to DC power, followed by the switching on and off of the power transistors, causing a voltage waveform at the desired frequency. This waveform then adjusts output voltage according to the preferred designated value. The three-phase induction motor is most commonly applied to a Variable Frequency Drive because it offers versatility and cost-effectiveness in comparison to a single-phase or synchronous motor.

Though they can be advantageous in some circumstances, a Variable Frequency Drive system often utilizes motors that are designed for fixed-speed operation. Variable Frequency Drive operator interfaces allow for the user to adjust operating speed, and start and stop the motor. The operator interface might also allow the user to switch and reverse between automatic control, or manual speed adjustment.

Advantages of a Variable Frequency Drive - Process temperature can be controlled without a separate controller - Low maintenance - Longer lifespan for the AC motor and other machinery - Lower operating costs - Equipment in the system that cannot handle excessive torque is protected. Types of Variable Frequency Drives. There are three common Variable Frequency Drives VFDs that offer both advantages and disadvantages depending on the application they are used for.

The three common VFD designs used include: However, there is a fourth type of VFD called Flux Vector Drive, which is emerging in popularity among end-users for its closed-loop control feature. Although the sections of each VFD are similar, they require a variation in circuitry in how they supply the frequency and voltage to the motor. The DC Link for this type of variable frequency drive uses an inductor to regulate the current ripple and to store the energy used by the motor.

These thyristors behave like switches which are turned on and off to create pulse width modulation PWM output that regulates the frequency and voltage to the motor. CSI variable frequency drives regulate current, require a large internal inductor and a motor load to operate. An important note about CSI VFD designs is the requirement of input and output filters which are necessary due to high harmonics in the power input and poor power factor. To work around this issue, many manufacturers implement either input transformers or reactors and harmonic filters at the point of common coupling users electrical system connected to the drive to help reduce the effects harmonics have on the drive system.

Regenerative power capability means that power is driven back from the motor to the power supply can be absorbed. These transistors or thyristors behave like switches which are turned on and off to create a pulse width modulation PWM output that regulates the frequency and voltage to the motor. The DC Link uses large capacitors to remove the ripple evident after the rectifier and creates a stable DC bus voltage. The six-step inverter stage of this driver uses high power rated IGBTs which turn on and off to regulate the frequency and voltage to the motor.

These transistors are controlled by a microprocessor or motor IC which monitors various aspects of the drive to provide the correct sequencing. This produces a sine-like waveform output to the motor. So how does turning a transistor on and off help create the sine-like wave output? By varying the voltage pulse width you are obtaining an average power which is the voltage supplied to the motor. The frequency supplied to the motor is determined by the number of positive to negative transitions per second.

In order to select the appropriate AC Motor for a given application, one needs to determine basic specifications. Calculate the required load torque and operating speed. Remember that induction and reversible motors cannot be adjusted; they require a gearhead. If this is needed, select the appropriate gear ratio.

Next determine frequency, and power supply voltage for the motor. Troubleshooting an AC Motor. Technical assistance regarding its AC Motor product line, as well as all the products manufactured or distributed by Anaheim Automation, is available at no charge. This assistance is offered to help the customer in choosing Anaheim Automation products for a specific application. In all cases, determination of fitness of the custom AC Motor in a specific system design is solely the customers' responsibility.

While every effort is made to offer solid advice regarding the AC Motor product line, as well as other motion control products, and to produce technical data and illustrations accurately, such advice and documents are for reference only, and subject to change without notice. The following steps may be taken to troubleshoot an AC Motor and Controller system:. Check the motor's smell. If there is a burning smell, replace the motor immediately. Check the motor's input voltage. Ensure wires are not damaged and the proper power supply is connected. Listen for loud vibration or squeaking noises.

Such noises may indicate damaged or worn-out bearings. If possible, lubricate the bearings, otherwise replace the motor completely. Use compressed air to rid the motor of debris, allow to cool, and restart. AC Motors that make an effort to start but fail, may be a sign of a bad starting capacitor.

Check for any signs of leaking oil, and replace the capacitor if this is the case. Ensure the application the motor is rotating is not locked up. Do this by disconnecting the mechanism and try running the motor by itself. The AC Motor can be a reasonable cost-effective solution to your application requirements. The construction materials along with how the motor is designed, make AC Motor systems an affordable solution. The AC Motor operates with a rotating magnetic field and does not use brushes.

This enables the cost of the motor to be lower, and eliminates the component that could wear over time. AC Motor products do not require a driver to operate. This saves initial setup costs. Today's manufacturing processes makes producing AC Motor products easier and quicker than ever.

The stator is made out of thin laminations that can be pressed or punched out of a CNC machine. Many other parts can be quickly made and perfected saving both time and money! Anaheim automation offers a full line of AC Motor products to choose from.

Typically, the AC Motor consists of two main components: The stator is the stationary part of the motor, consisting of several thin laminations wound with an insulated wire, forming the core. The rotor is connected to the output shaft on the inside. The most common type of rotor used in an AC Motor is the squirrel cage rotor, named after its resemblance to rodent exercise wheels. The stator mounts inside the motor's enclosure, with the rotor mounted inside, and a gap separating the two from touching each other.

The enclosure is the motor's frame, containing two bearing houses. Formulas for an AC Motor. AC Motor — An electric motor that is driven by an alternating current, as opposed to a direct current. Alternating Current — Electric charge that frequently reverse in direction Opposite of direct current, with charge in only one direction. Centrifugal Switch — The electric switch that controls the rotational speed of a shaft, operating off of the centrifugal force generated from the shaft itself.

Gear Ratio — The ratio at which the motor's speed is reduced by the gearhead. The speed at the output shaft is 1 Gear Ratio x the motor speed. Inverter - The device that converts direct current to alternating current. Reverse of the Rectifier. Induction Motor — Can be referred to as asynchronous motor; type of AC motor where electromagnetic induction supplies power to the rotor. Slip is required to produce torque. No Load Speed — Typically lower than synchronous speed, it is the speed when the motor is not carrying a load.

Rated Speed — The speed of the motor at rated output power. Typically the most sought-after speed. Rectifier — The device that converts alternating current to direct current within a motor.


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  5. They can be utilized as a component in a power supply, or can detect radio signals. Typically rectifiers may consist of solid state diodes, mercury arc valves, or other substances. Reverse of the inverter. Rectification — The process by which alternating current is converted to direct current by means of a rectifier within an AC Motor.

    Split Phase Induction Motor — Motors that can generate more starting torque by using a centrifugal switch combined with a special startup winding. When the discrete steps are mechanical, that can cause higher power drain, wear on the parts, and undesirable user experience. This is not actually particularly rare. In industrial systems, stepper motors with encoder feedback are relatively common. And for hobbyists, there is e. The only drawback compared to open-loop stepper systems is the price. However, the real competitor is closed-loop BLDC motors, which have advantages over closed-loop steppers:.

    This is the reason why in industrial projects BLDC motors are getting more and more common in closed-loop systems. But for hobbyist, stepper motors with high torque can often be cheaper than BLDCs with similar torque, and it is also mechanically an easy upgrade from normal stepper motor. Provided you don't miss a step , a stepper motor should give you a deterministic movement. You can run it N steps forwards and N steps backwards and it will be in the same place.

    This is because the steps are discrete. Problems arise if it jams or you try to drive it too fast. Many systems have a simple means of resetting to a known state through a limit switch. I've worked with systems that achieved extremely precise rotational positions and rates by microstepping stepper motors that then drove a worm gear unidirectionally. The key to that system is a linear encoder wrapped round the rotating part, which gives you you closed loop.

    This was positioning a diffraction grating in a spectrometer. Some motorised microscope stages also use a linear encoder close to the specimen. In this application the load or its leverage may change by enough that the mechanism deforms or its backlash changes, meaning that counting steps from a reference switch no longer gives an accurate position. This may or may not be used ion a closed-loop configuration i.

    By clicking "Post Your Answer", you acknowledge that you have read our updated terms of service , privacy policy and cookie policy , and that your continued use of the website is subject to these policies. Home Questions Tags Users Unanswered. Why aren't Stepper motors used in closed-loop systems and PID control? Picture a stepper motor design that points a photodetector at a moving point light source.

    For example you can do backchannel analysis to detect missed steps with steppers: I believe, often step motors are used without feedback open loop because the designer is lazy. A good designer is lazy, not doing more than necessary. If no feedback is needed, the keep it open loop. Being lazy is one way of keeping costs down. Added As Dmitry pointed out in a comment, a control loop around something that can only be adjusted in discrete steps can very easily lead to oscillation.

    Olin Lathrop k 30 Additionally, PID controllers with a large I factor will oscillate endlessly between two adjacent positions of a stepper. I've added that to the answer.

    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors) Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)
    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors) Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)
    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors) Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)
    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors) Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)
    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors) Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)
    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors) Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)
    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors) Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)
    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors) Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)
    Stepping Motors: A Guide to Theory and Practice (Control Engineering) (Control, Robotics and Sensors)

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