Månadsvis arkiv: oktober 2016
This chapter has explained how to operate steppers by energizing one or two winding pairs at a tiem, but tere are a number of different ways to drive a Nema 23 stepper motor, and this discussion touches on four of them:
* Full-step (one phase on) mode – Each control signal energizes on winding.
* Full-step (two phases on) mode – Each control signal energizes two windings.
* Half-step mode – Each control signal alternates between energizing one and two windings.
* Microstep mode – The controller delivers sinusoidal signals to the stepper’s windings.
Full-Step (One Phase On) Mode
The simplest way to control a stepper is to energize one winding at a time. This is the method discussed at the start of this chapter. Figure 4.15 shows what the signaling sequence looks lide when controlling a stepper motor drive in this mode.
With each control signal, the rotor truns to align itself with the energized winding. The rotor always turns through the stepper’s rated step angle. That is, if a PM motor is rated for 7.5, each control signal causes it to turn 7.5.
Full-Step (Two Phase On) Mode
In the full-step (two phase on) mode, the controller energizes two windings at once. This turns the rotor through the stepper’s rated angle, and the rotor always aligns itself between two windings. Figure 4.16 illustrates one rotation of a stepper motor driven in this mode.
Figure 4.17 shows what the corresponding drive sequence looks like.
The main advantage of this mode over full-step (one phase on) is that it improves the motor’s torque. Because two windings are always on, torque increases by approximately 30%-40%. The disadvantage is that the power supply has to provide twice as much current to turn the stepper.
The half-step mode is like a combination of the two full-step modes. That is, the controller alternates between energizing one winding and two windings. Figure 4.18 depicts three rotations of a stepper in half-step mode.
Figure 4.19 illustrates a control signal for a stepper motor driven in half-step mode.
In this mode, the rotor aligns itself with windings (when one winding is energized) and between windings (when two windings are energized). This effectively reduces the motor’s step angle by half. That is, if the stepper’s step angle is 1.8, it will trun at 0.9 in half-step mode.
The disadvantage of this mode is that, when a single winding is energized, the rotor turns with approximately 20% less toruqe. This can be compenstated for by increasing the current.
The purpose of microstep mode is to have the stepper turn as smoothly as possible. This requires dividing the energizing pulse into potentially hundreds of control signals. Common numbers of division are 8,64,and 256. If the energizing pulse is divided into 256 signals, a 1.8 stepper will turn at 1.8/256=0.007 per control signal.
In this mode, the controller delivers current in a sinusoidal pattern. Successive windings receive a delayed version of this sinusoid. Figure 4.20 gives an idea of what this looks like.
Using this mode reduces torque by nearly 30%， but another disadvantage involes speed. As the width of a control signal decrease, the ability of the motor to respond also decrease. Therefore, if the controller delivers rapid pulses to the stepper in microstep mode, the motor may not turn in a reliable fashion.
The stator consists of a cylindrical frame and a stator core. The stator core is located in the frame and an armature coil is wound around the stator core. The end of the coil is connected with a lead wire and current is provide from the lead wire. The rotor consists of a shaft and a permanent magnet and the permanent magnet is attached to the outside of the shaft. In a synchronous type AC Leadshine servo motor, the magnet is attached to a rotor and an armature coil is wound around the stator unlike the DC servo motor. Therefore, the supply of current is possible from the outside without a stator and a synchronous type AC servo motor is called a “brushless servo motor” because of this structural characteristic. Because this structure makes it possible to cool down a stator core directly from the outside, it is possible to resist an increase in temeprature. Also, because a synchronous type AC servo motor does not have the limitation of maximum velocity due to recification spark, a good characteristic of torque in the high-speed range can be obtained. In additon, because this type of motor has no brush, it can be operated for a long time without maintenace.
Like a DC servo motor, this type of AC servo motor drive uses an optical encoder or a resolver as a detector of rotation velocity. Also, a ferrite magnet or a rate earth magnet is used for the magnet which is built into the rotor and plays the role of a field system.
In this type of AC Servo Motor, because an armature contribution is linearly proportional to torque. Stop is easy and dynamic brake wordks during emergency stop. However, because a permanent magnet is use, the structure is very complex and the detection of position of the rotor is needed. The current from the armature includes high frequency current and the high frequecy current is the source of toruqe ripple and vibration.
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 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.
cp1e e20sdr a 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.
★ 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
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
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.