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  • 21 Sep 2016
    A Comparison between the DC servo motor and AC servo motor, showing their advantages and disadvantages, is shown in Table 4.6. AC Panasonic servo motor are simple in construction, durable and are suitable for use in industiral robots employed under rigorous conditions and as drive sources for industrial machines. This is one of the reasons for utilization of AC motors. As a measuring instrument,steppming motors (pulse motors) are used because the control system can be configured with the simple open loop. That is, the rotation angle proportional to the number of pulses can be easily obtained. On the other hand, for AC servo motors it is necessary to have feedback on rotation angle from detector. Moreover, in contrast to the DC motors, as they have 3 phase power supply the complications of the control devices cannot be avoided. AC Motor The AC motor's stator has coils which are supplied using the alternating present and produces a rotating magnetic field. The AC motor’s rotor rotates inside the motor’s coils and is attached to an output shaft that produces torque by the rotating magnetic field. You will find two various kinds of AC yaskawa servo motor and every of them utilizes a various kind of rotor. The very first kind of AC motor is known as an induction motor (also referred to as an asynchronous motor). An induction motor utilizes a magnetic field around the rotor of an induction motor that is produced by an induced present. The other kind of AC motor is known as a synchronous motor and rotates precisely in the provide frequency or on a sub-multiple from the provide frequency. A synchronous motor is able to operate with precision supply frequency because it doesn’t reply on induction. The magnetic field on a synchronous motor is generated by current delivered through slip rings or a permanent magnet. Synchronous motors run faster than induction motors because the speed is reduced by the slip of the asynchronous motor. DC motors Difference Between AC and DC motors are powered from direct current (DC) power and are mechanically commutated machines. DC motors have a voltage induced rotating armature winding, and a non-rotating armature field frame winding that is a static field, or permanent magnet. DC motors use different motor connections of the field and armature winding to produce different speed and torque regulation. Unlike AC motors, DC motor speed can be controlled within the winding by changing the voltage applied to the DC motor armature, or by adjusting the field frame current. DC motor is the rotating motor that is capable of converting DC energy into mechanical energy (DC motor) or converting mechanical energy into DC energy. When the DC motor is running as a DC motor, it converts electrical energy into mechanical energy; when the DC motor is running as a generator is running, it converts mechanical energy into electrical energy. Conclusion AC and DC motors use the same principle of using an armature winding and magnetic field except with DC motors, the armature rotates while the magnetic field doesn’t rotate. In AC motors the armature doesn't rotate and the magnetic field continuously rotates. In some applications today, DC electric motors are replaced by combining an AC electric motor with an electronic speed controller, known as variable frequency drives. DC electric motors are substituted for an AC electric motor and an electronic speed controller because it is a more economical and less costly solution.
    122 Posted by claire rong
  • 23 Sep 2016
    A gear motor develops an output torque at its shaft by allowing hydraulic pressure to act on gear teeth. Gear reduction motors consists basically of a housing with inlet and outlet ports, and a rotating group made up of two gears. One gear is attached to a shaft that is connected to a load. The other gear is the driven gear. The various commonly used gear motors are shown in Fig.2.16.   In a gear motor, the imbalance necessary for motor operation is caused by gear teeth unmeshing. The inlet is subjected to system pressure and the outlet is at return line pressure. As the gear teeth unmesh, all teeth subjected to system pressure are hydraulically balanced except for one side of one tooth on one gear tooth. The larger the gear tooth or the higher the pressure,the more torque is produced. An internal gear motor consists of one external gear which meshes whith the teeth on the inside circumference of a larger gear. A popular type of internal worm gear motor in industrial systems is the gerotor motor. This motor is an internal gear motor with an inner drive gear and an outer driven gear which has one more tooth than the inner gear. The inner gear is attached to a shaft which is connected to a load. The imbalance in a gerotor motor is cuased by the difference in gear area exposed to hydraulic pressure at the motor inlet. Fluid pressure acting on these unequally exposed teeth results in a torque at the motor shaft. The larger the gear or the higher the pressure, the more torque will be developed at the shaft. Fluid entering the rotating group of a gerotor motor is separated from the fluide exiting the motor by means of a port plate with kindey-shaped inlet and outlet ports. When selecting a gear motor, an important consideration is the degree of gear service and gear life based on the load conditions to which the motor will be subjected. Gear motors are divided into three classes. Each class uses different gear sizes to handle specific load conditions. Each class gives about the same life for the gears. The American Gear Manufacturer's Association has defined three operating conditions commonly found in industrial service and has established three standard gear classifications to meet these conditions: Class I    For steady loads within the motor rating of 8 hours per day duration, or for intermittent operation under moderate stock conditions.Class II   For 24-hour operation at steady loads within the motor rating, or 8-hour operation under moderate shock conditions.Class III  For 24-hour operation under moderate shock condition, or 8-hour operation under heavy shock conditions. For conditions that are more severe than those covered by Class III gears, a fluid drive unit may be incorporated in assembly to cushion the shock to an acceptable value. To achieve multiple speeds, separte units are available with a transmission comparable to that of an automobile. These units must be assembled with the motor and the driven machine. Because the amout of power lost in gearing is very small, the multiple drive has essentially constant horsepower. In other words, as the output speed is decreased, the torque is increased. Generally, this means that larger shaft sizes are needed for the output side.
    118 Posted by claire rong
  • 26 Oct 2016
    While individual gears cn be purchased and installed into stage machinery, it is far easier, more reliable, and in the long run less costly to purchase manfactured gear reducer motor. The reducer case will hold the gears in proper alignment; bathe the gears in lubrication oil; keep out dust, dirt, and straying fingers; absorb some of the gear noise; and provide various options for mounting the reducer to a frame and the motor to the reducer. Figure 15.3 shows a typcial gear reducer. Parallel shaft reducers, not surprisingly, have output shafts parallel to their inputs. They use helical or spur gears in pairs, or in multi-pair stages, to creat speed recution. They are extremely efficient, as much as 98%, although this efficiency comes with a high price tag. Multiple reduction stages are used even for low reduction ratios, and the cost of many pairs of gears adds up. For a given ratio and power handling capacitya parallel shaft reducer will usually cost 1 to 4 times the cost of a worm reducer. In industrial use, the power savings that result from high efficiency defray the cost of the reducer. For theatre, where maechanized effects usually run for only minutes or even seconds a night, the cost of power lost is not a concern. The high efficiency can even be, at times, a disadvantage since the redcuer will creat little braking or holding effect on a load at the output. Recently serveral brands of helical and helical-bevel reducers have appeared in gear-breakmotor combinations at significantly lower cost, which has led to an increase in their use in theatre. Planetary gear reducers are subset of parallel shaft reducers which use spur and internal gears. They are similar to parallel shaft reducers in terms of cost and efficiency, but tend to be smaller for a given torque rating. This is because multiple spur gears contact the internal gear simultaneously, sharing the load and providing a high strength to size ratio which makes them a popular choice for use with servo motors, which are also very compact. Right angle gear reducers, predictably, have an output shaft perpendicular to the input. The two shafts are typically vertically offset from each other, and this offset amout is referred to as the center distance. The most commonly used right angle reducer is the worm gear reducer, which utilizes a worm and a worm gear. The worm, which has the general appearance of a piece of threaded rod, is enmeshed with the worm such that the worm threads push the worm gear teeth. Worm gears are a very common type of gearing used for stage machinery because they * are commonly available with reduction rations up to 70:1 in single stage (multiple stage reducers go up to at least 3600:1) * are relatively small compared to equivalent parallel shaft reducers * are inherently quiet * are relatively inexpensive compared to equivalent capcity parallel shaft reducers The one major quirk of worm gear redcuers is generally low efficiency, which is a complex function of many factors including speed, lubrication, geometry of the gears, wear, vibration, ect. This inefficiency can in some applications be an advantage since it can help to brake or hold loads, but "help" is the key word here.
    104 Posted by claire rong
  • 14 Oct 2016
    In the first module, you learned about the basic architecture and operation of the Allen-Bradley Micrologix 1000, including a brief introduction to its I/O system. This second module goes into more detail about the I/O system of the Micrologix 1000 Omron PLC. It includes four sections: 1. Types of input/output devices 2. Input interfaces 3. Output interfaces 4. System and I/O power distribution wiring Types of Input/Output Devices A MicroLogix 1000 PLC uses its input and output interfaces to connect with field input/output devices. To review, all input devices provide a signal to the PLC, and all output devices receive a signal from the PLC. All I/O devices, however, do not send and receive the same type of signal. There are two different types of I/O signals and two types of I/O devices that use them. The two types of I/O devices are discrete devices and analog devices. At the end of this section, you will know: • the difference between the two types of I/O devices • which type works with the MicroLogix 1000 Discrete Devices Discrete devices are input or output devices that provide or receive discrete digital signals. A discrete digital signal is one that can report only two states, such as ON/OFF or open/closed. A limit switch is an example of a discrete input device because,1at any given time, it is either open or closed. It sends a discretePLdigital signal to a PLC. This signal can have one of only two values, 0 or 1, indicating that the device is either OFF or ON, respectively (see Figure 2-1). A pilot light is an example of a discrete output device (see Figure 2-2). It can only be ON or OFF. A discrete output deviceOFFDiscrete0receives a discrete digital signal from a PLC telling it to be in either one state or the other. A discrete output can never be in a state in between ON and OFF.Figure 2-2. A pilot light receives a discrete signal from a PLC. Next article we will continue introducing Analog Devices. The following products are some hot sale OMRON PLC on our store. CP1H XA40DT D OMRON PLC, CP1E CPU AC 100-240V input, 24DI 16DO Relay, USB port, Original brand new CP1E series offers all functionality you need to control relatively simple applications, including outstanding positioning capability. All CP1E CPUs offer high-speed USB for quick programming. The “Easy Input Editor” software feature allows faster programming by using an intuitive ladder editor to create an organized application program. The CP1E series comes in two different types: CP1E-E is the most economical, while the CP1E-N has a built-in real-time clock, motion control capabilities, and a serial port to connect an HMI, barcode reader, or other serial device. Several optional units are available to increase the functionality. As the CP1E series shares the same architecture as the CP1L, CP1H, CJ, and CS series, programs are compatible for memory allocations and instructions. Features: ★ New CP1E CPU Units now available. -Lineup including CPU Units with built-in three ports: USB, RS-232C, RS-485. -The depth of CPU Units with RS-232C connectors is reduced by 20 mm. (N30/40/60S(1)) ★ Easy connection with computers using commercially available USB cables. ★ With E30/40/60(S), N30/40/60 or NA20 CPU Units, Add I/O, Analog I/O or Temperature Inputs by Connecting Expansion Units or Expansion I/O Units. ★ Input interrupts ★ Complete High-speed Counter Functionality. ★ Versatile pulse control for Transistor Output for N14/20/30/40/60 or NA20 CPU Units. ★ PWM Outputs for Transistor Output for N14/20/30/40/60(S@) or NA20 CPU Units. ★ Mounting Serial Option Boards or Ethernet Option Board to N30/40/60 or NA20 CPU Units. ★ Built-in analog I/O, two inputs and one output, for NA-type CPU Units. CP1H-XA40DT-D PLC OMRON, CPU 24VDC, input 24 point transistor output 16 point Original brand new Features: Pulse output for 4 axes. Advanced power for high-precision positioning control High-speed counters. Differential phases for 4 axes Easily handles multi-axis control with a single unit Eight interrupt inputs are built in. Faster processing of approximately 500 instructions speeds up the entire system Serial communications. Two ports. Select option boards for either RS-232C or RS-485 communications EtherNet communications, enabled by using an option board, two ports can be used as an EtherNet port to perform, EtherNet communications between the CP1H and a host computer USB peripheral port The structured text (ST) language, makes math operations even easier LCD displays and settings, enabled using option board Transistor output (sinking) CJ1W-ID211 PLC OMRON I/O 16 input point 24VDC Original brand new Features: High-speed input models are available, meeting versatile applications. ON Response Time: 15μs, OFF Response Time: 90μs Use 24-VDC, 100-VAC, and 200-VAC models to connect to devices with different types of outputs. The 24-VDC models can be connected to devices with either NPN or PNP outputs. There is no need to select the polarity. *1 A digital filter in the Unit can be set from 0 to 32 ms to reduce the influence of external noise. Either a Fujitsu or MIL connector interface can be used. *2 Several models of Terminal Block Conversion Units are available, making it easy to connect to external devices.
    101 Posted by claire rong
Technology 1,084 views Sep 07, 2016
Mechanical Overview of Servo Motors

Servo motors have serval distinct characteristics that sperate them from their stepper counterparts. The biggest is the lack of direct gearing between the rotor and the output shaft. This eliminates the backlash and cogging behaviors found ins steppers, where there is period of slop between the gear teeth before movement actually begins, and where the shaft continues to move after the motor has stopped. This can lead to jerky starts and stops, as well as a time delay in movement. This does not impede static positioning performance markedly, but it presents major issues when on-the-fly velocity changes or hard starts/stops are needed.

A model of a typical radial brushless DC servo motor is shown before in figure 1.1 For a long time, yaskawa servo motor used brushes to transfer current from the static winding to the rotor, but this would lead to wear on the brushes, in turn shortening the lifespan of the motor. With the advent of electronic motor controllers, the brusheless design was adopted, which uses control electronics to vary the currents phases to the motor's windings in the same way the brushes do. For the rest of this paper, all mention of servo motors will be of the brusheless type.

Looking at figure 1.1 below, there are several objects of interest. First are the armature windings (held by the stator), which create a magnetic field that travels through the air gap to the permanent magnets on the rotor. Even though there are normally no gears in a servo motor, cogging can still exist, as there are gaps between the magnets on the rotor where the flux decrease, though this only becomes noticeable at low speeds. This type of congging in servos is perhaps more accurately termed "detent torque." There are two ways to minimize this type of cogging, the most common being the addition of some gearing to the drive shaft. This allow the mitsubishi servo motor to run at a higher speed out of its cogging region, but does not compromise power output or precision, thought it can induce some backlash. The other way of minimizing cogging is to skew the magnets on the rotor so that a radial line from the center of the rotor always intersects a magnet at least once. When using a motor without gearing, it is known as a direct drive motor. This allows for the best transfer of power to the load, and avoids any of the negative aspects of gearing previously mentioned. A feature in newer servo motors (including the Bodine models used in this thesis) is the use of an ironless stator, which eliminates iron saturation, a situation where the magnetic properities of the iron limit how much current can be applied to the windings. Inducing iron saturation too ofen will cause overheating and possibly damage the winding or magnets. With an ironless stator, rotor magnet skewing is not necessary, as the magnetic fields aren't influenced by the material of the stator. Also, since the only mechanical connection between the shaft and the body is through the bearings, friction is very low (especialy when using ball bearings).

In high torque motors such as the ones used in this thesis, the rotor actually consists of two plates of permanet magnets sandwiching the stator, which allows for a major increase in torque. This feature only exists in axial flux motors, due to the design where the stator lies in between the rotors, whereas in radial flux servos, the rotor is completely enclosed by the stator. The majority of the heat dissipated from a servo motor comes from the stator, so its outside location adis in cooling. In fact, the main limiting fator in the power of a servo motor is the heat capacity of the stator and the armature windings.

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