Some people say that stepper motor system does not need closed-loop, itself is open-loop, but not more than the use of the range can be, and this view I do not agree. I have the following is the point of view:
Closed-loop Stepper system is cheaper than the servo system, in the field of automatic control stepper system used in most of the use,But the possibility of stepping out of the stepping system, and do not know whether it has been out of step and there are step-by-step drive can subdivide and produce micro-step, but the stepper system is mainly to make the current more smooth, Although it can improve the stepping power Machine accuracy, but the micro-step is not reliable.
Because of this, the stepping system is limited to the requirements of high precision and high risk requirements of the machine.With a closed-loop controller, the stepper system accuracy is no worse than the servo, but the speed is not comparable to the servo,If you can use the Linear Scale on the market, the positioning accuracy can exceed the servo motor, because the servo is only semi-closed loop Control, and stepper motor with closed-loop controller and the grating is fully closed-loop control, eliminating the mechanical system error,So the positioning accuracy can be more than the servo system, while the price is only 1 / N servo.
Stepper motor can not guarantee absolute accuracy, but also do not know whether it is accurate, so the workload changes or uncertain working conditions, such as CNC milling machine, engraving and milling machine cutting force changes are uncontrollable, such as In the steel layer of a deep groove milling, to the multi-layer after each cutter, close to the edge of the groove when the cutting force will increase dramatically, in order to cope with this possibility and to ensure accuracy, the only way is to reduce The entire processing speed, in exchange for local safety, and in fact most of the working hours are not in a large resistance state, so a serious reduction in the efficiency of the system.The use of closed-loop controllers can significantly improve the efficiency of the machine in this case, and you do not have to reduce the overall process and speed and efficiency for individual resistance points. The controller will automatically adjust the speed through the resistance point.
Automatically recovers the speed and accelerates the compensation back to the lost pulses, and is instantaneous to complete.If you set the alarm function, can be out of step to a certain situation, the alarm signal to the host computer servo system is the same way.
I have seen a lot of imported mechanical and electrical equipment there are some medical machines, stepper motor behind with an encoder,
To ensure the accuracy and safety of the equipment.
From the above points can be seen stepping motor closed-loop control is the existence of their own rationality and value,Of course, these are only for high demand but not on the servo of the machine, not for low-demand machines.
Its role is to fill the open loop of the stepper motor and high performance servo motor in the middle of the blank,Giving more choice.
Choosing the right DC Motor (or DC gear motor) for a specific application can be a daunting task and many manufacturers only provide basic motor specifications. These basic specifications might not be sufficient for your needs. Listed below are ideal motor specifications and whenever possible, ways to approximate values.
A truly quiet DC worm gear motor is often needed in medical applications not only to reinforce the quality of the deployed medical devices but also to not be a contributing source to ambient noise where concentration and communication are vital. While that is a driving factor in the development of the new DCmind line of DC brush motors from Crouzet Motors, what is even more important is the significant increase in both lifetime and efficiency that accompany that engineering development.
For DC electric motors in Minnesota and around the country, there are common specifications needed to design a motor.
Nominal Voltage – For DC electric motors, it is important to know the nominal voltage of the drive motor. The designer also needs to know if a motor is to be operated outside of the nominal voltage range for any period of time.
Horsepower Rating – This is the rating of the nominal work that the worm gear reducer is expected to perform. The power rating can be expressed in horsepower or watts. This requirement can also be stated as a combination of torque and speed. We will also need to know if the motor will run at different load points, as either under loading or overloading the motor are detrimental to its service life.
Rated speed – The motor designer needs to know how fast the motor is required to run in the application. We also need to know if there are times when this speed would change, either by using a speed control to vary the voltage supplied to the motor or by increasing or decreasing the load on the motor.
Duty cycle – As a Permanent Magnet DC Motor runs, the current passing through the windings causes heat to be generated, raising the temperature of the motor as time passes. As the motor reaches its continuous running load point, the temperature should stabilizes within an hour or so. If the temperature does not stabilize, you need a higher horsepower rated motor.
Stall Torque – The maximum amount of torque provided by a motor with the shaft not rotating is known as stall torque. Keep in mind that if a motor is subjected to stall conditions for more than a few seconds, it likely will sustain irreparable damage.
Inrush Current – This is the current that a motor draws upon start up, whether or not it is under load. This current drops immediately as the motor’s speed increases, but in some cases any attached electronics can become seriously damaged by the extremely high current. Sometimes motor components can be damaged also. In those cases a current limiter would be recommended.
My conclusion is that DC brushless drives will likely continue to dominate in the hybrid and coming plug-in hybrid markets, and that induction drives will likely maintain dominance for the high-performance pure electrics. The question is what will happen as hybrids become more electrically intensive and as their performance levels increase? The fact that so much of the hardware is common for both drives could mean that we will see induction and DC brushless live and work side by side during the coming golden era of hybrid and electric vehicles.
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.
AC motors are powered with alternating present and convert electrical power into mechanical power. You will find 3 kinds of alternating present motors with three-phases. AC induction motors probably the most generally utilized, for AC voltage, the voltage on which they run, is readily accessible at any outlet. All AC motors, regardless of their kind, are comprised of a stator, which produces the magnetic field, along with a rotor, that is produced to rotate by the magnetic field that’s induced in the present generated by the stator.
When selecting the proper stepper motor drive for the application you will find two important elements to bear in mind; the operating speed, or how quick the motor will turn as measured in RPMS, and also the beginning torque, or just how much force is required (if any) to begin the motor. By supplying these specifications to an skilled engineer, you are able to make sure you’ll obtain probably the most efficient and price effective AC motor for the application.
In contrast to toys and flashlights, most houses, offices, factories, as well as other buildings are not powered by small batteries: they are not supplied with DC present, but with alternating present (AC), which reverses its path about 50 occasions per second (having a frequency of 50 Hz). If you would like to run a motor out of your household AC electrical energy provide, rather than from a DC battery, you’ll need a various style of motor.
In an AC motor, there is a ring of electromagnets arranged about the outdoors (creating up the stator), that are developed to create a rotating magnetic field. Inside the stator, there is a strong metal axle, a loop of wire, a coil, a squirrel cage produced of metal bars and interconnections (just like the rotating cages individuals occasionally get to amuse pet mice), or some other freely rotating metal component that may conduct electrical energy. In contrast to inside a nema 17 stepper, exactly where you send energy towards the inner rotor, in an AC motor you send energy towards the outer coils that make up the stator. The coils are energized in pairs, in sequence, creating a magnetic field that rotates about the outdoors from the motor.
How does this rotating field make the motor move? Keep in mind that the rotor, suspended inside the magnetic field, is definitely an electrical conductor. The magnetic field is continuously altering (simply because it is rotating) so, based on the laws of electromagnetism (Faraday’s law, to become precise), the magnetic field produces (or induces, to make use of Faraday’s personal term) an electric present inside the rotor. When the conductor is really a ring or perhaps a wire, the present flows about it inside a loop. When the conductor is merely a strong piece of metal, eddy currents swirl about it rather. Either way, the induced present produces its personal magnetic field and, based on an additional law of electromagnetism (Lenz’s law) tries to quit what ever it’s that causes it’s the rotating magnetic field by rotating also. (You are able to believe from the rotor frantically attempting to “catch up” using the rotating magnetic field in an work to get rid of the distinction in motion in between them.) Electromagnetic induction will be the important to why a motor like this spins and that is why it is known as an induction motor.
Hybrid stepper motors provide excellent performance in areas of torque, speed, and step resolution. Typically, step angles for a hybrid stepper motor range from 200 to 400 steps per revolution. This type of CNC stepper motor provides a combination of the best features available on both the PM and VR types of stepper motors.
Figure 8.1 shows a simplified construction of a unipolar hybrid stepper motor.The rotor of this machine consists of two star-shaped milled steel pieces with three teeth on each. A cylindrical, axially magnetized PM is placed between the milledpieces making the end of each rotor either a north or a south pole. The teeth areoffset at the north and south ends as shown in Fig. 8.1. The stator has four poles, each of which has a center-tapped winding. Since all the windings have the commonconnection V+, only five wires, A, B, C, D, and V+, leave the motor. A winding is excited by sending current into the V+ wire and out one of the other wires. Thewindings are wound in the stator teeth in such a way so that the Closed Loop Stepper motor behaves in the following way:
If winding A or C is excited, pole 1 or pole 3 is energized as south.
If winding B or D is excited, pole 2 or pole 4 is energized as
Stepper motors are also classified with respect to the stator windings as being either bipolar or unipolar.Bipolar stepper motors have two windings with anopposing magnetizing effect in each pole, while unipolar stepper motors use only one winding per pole.
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The HBS series offers an alternative for applications requiring high performance and high reliability when the servo was the only choice, while it remains cost-effective. The system includes a 2-phase stepper motor combined with a fully digital, high performance drive and an internal encoder which is used to close the position, velocity and current loops in real time, just like servo systems. It combines the best of servo and stepper motor technologies, and delivers unique capabilities and enhancements over both, while at a fraction of the cost of a servo system.
Stepper based servo control
Direct 120 / 220 / 230 AC input, or DC to 100V
Closed position loop to eliminate loss of synchronization
No torque reservation
Load based output current for extra low motor heating
Smooth motor movement and low motor noise
Quick response and no hunting
No overshooting and almost zero settling time
High starting torque, high inertial loads
Capable of driving NEMA 23, 24, 34, and 42 easy servo motors (stepper motors with encoders)
Plug-and-play, no tuning for most of applications
2 Phase Encoder closed loop Stepper Motor+Drive Kit Engraving Machine
2HSS two phase hybrid stepper servo drive system integrated servo control technology into the digital step driver. It adopts typical tricyclic control method which include current loop,speed loop and position loop.This product has the advantage of both step and servo system, is a highly cost-effective motion control products.
Full closed loop
1.Accurate position and speed control can achieve the most strict request of the application.
2. High robustness’s servo control adapt to wide range change of inertial load and friction load.
3.The motor with 1000 CPR encoder,support vector closed loop control. Compare with traditional step motor, it solved the problem of lose step.
Low heat/high efficiency
1.Adjust the current according to actual load,the heat is much lower compare with traditional step motor.
2.The current is almost 0, and without heat under stop condition.
3.It save energy and can achieve nearly 100% torque output. Working smoothly and accurate.
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Our main products are stepper motor drives, step motor, AC servo motor systems, DC brushes and brushless motors and drive systems, and intelligent step motors .we also provide complimentary mechanical products, such as motor couplings, gearboxes, and linear motions.
Stepper motors can be used in various areas of your microcontroller projects such as making robots, robotic arm, automatic door lock system etc. This tutorial will explain you construction of Nema 42 stepper motor (unipolar and bipolar stepper motors ), basic pricipal, different controlling types (Half step and Full step), Interfacing Techniques (using L293D or ULN2003) and programming your microcontroller in C and assembly to control stepper motor.
Types of Stepper Motors
There are basic two types of stepper motors available in market.
Unipolar stepper motor
The unipolar stepper motor has five or six wires and four coils (actually two coils divided by center connections on each coil). The center connections of the coils are tied together and used as the power connection. They are called unipolar steppers because power always comes in on this one pole.
Bipolar stepper motor
The bipolar Linear Stepper Motor usually has four wires coming out of it. Unlike unipolar steppers, bipolar steppers have no common center connection. They have two independent sets of coils instead. You can distinguish them from unipolar steppers by measuring the resistance between the wires. You should find two pairs of wires with equal resistance. If you’ve got the leads of your meter connected to two wires that are not connected (i.e. not attached to the same coil), you should see infinite resistance (or no continuity).
As already said, we will talk mostly on “Unipolar stepper motors” which is most common type of stepper motor available in the market.A simple example of 6 lead step motor is given below and in 5 lead step motor wire 5 and 6 are joined together to make 1 wire as common.
Unipolar versus bipolar stepper motor interface
There are three common types of stepper motor interfacing: universal, unipolar, and bipolar. They can be identified by the number of connections to the motor. A universal stepper motor has eight, while the unipolar has six and the bipolar has four. The universal stepper motor can be configured for all three modes, while the unipolar can be either unipolar or bipolar. Obviously the bipolar cannot be configured for universal nor unipolar mode. Table 17-7 shows selected stepper motor characteristics. Figure 17-10 shows the basic internal connections of all three type of configurations.
Unipolar stepper motors can be controlled using the basic interfacing shown in Figure 17-11, whereas the bipolar stepper requires H-Bridge circuitry. Bipolar stepper motors require a higher operational current than the unipolar; the advantage of this is a higher holding torque.
The diagram below shows the interfacing of stepper motor to a micro-controller. This is general diagram and can be applied to any micro-controller family like PIC micro-controller, AVR or 8051 micro-controller.
Since, the micro-controller cannot provide enough current to run the motor, a driver like a ULN2003 is used to drive the motor. Similarly, individual transistors or any other driver IC can also be used to drive the motor. See to it that if required, the external pull up resistors is connected to pins depending on the micro-controller you use. The motor must never be directly connected to the controller pins. The motor Voltage depends on the size of the motor. A typical 4 phase uni-polar stepper motor has 5 terminals. 4 phase terminals and one common terminal of the center tap that is connected to ground.
The programming algorithm for continuous rotation in clockwise mode is given below:
Initialize the port pins used for the motor as outputs
Write a common delay program of say 500 ms
Output first sequence-0 × 09 on the pins
Call delay function
Output second sequence-0 × 0 c on the pins
Call delay function
Output third sequence-0 × 06 on the pins
Call delay function
Output fourth sequence-0 × 03 on the pins
Call delay function
Go to step 3
Before the closed-loop system can be simulated it is necessary to choose appropriate values for yaskawa servo motors and load parameters. Every set of parameter values will, of course, lead to a unique simulation result, but in this paper it is only possible to present results corresponding to a single set of values. Some typical set of parameter values must therefore be selected.
A type 23HS-108 motor was chosen for the simulations because it typifies small hybrid Nema 23 stepper motor. The stator windings are assumed to be excited by a 24 V, 2 A bipolar chopper drive.
Choice of the load parameters is more difficult because there really is no typical load. As a general rule, however, the load inertia will not normally greatly exceed the motor inertia and for the purpose of these simulations the total inertia will be assumed to be equal to the motor inertia. Coulomb and viscous friction in the load usually dominate the motor friction. Up to a point the performance of the closed-loop system described here improves with increasing friction because friction provides the only significant damping of overshoot. The worst-case assumption is that the load friction is zero, and in the simulations presented here the total friction is assumed to be equal to the motor friction. In any real system the overshoot is likely to be less serious than that predicted by the simulations.
The results of the simulations are displayed in graphical form with the rotor angular velocity dmpos/dt (expressed in steps/s) plotted against positional error mpos-cpos (expressed in steps). There are three important situations to consider, all of which may lead to loss of synchronization in open-loop systems: operation at a resonant rate, operation above the maximum start-stop (pull-in) rate and excessive load torque.
Loss of synchronization due to resonance is only observed in lightly damped systems, particularly if an 8-step sequence is used. Figure 3 shows the response of open-loop and closed-loop systems to a sequence of 20 steps at the resonant rate of 153 steps/s. Both systems start from rest with zero positional error. In the case of the open-loop system the positional error builds up over several steps until at the 6th step the error exceeds 4 steps and synchronization is lost. This does not happen in the closed-loop system where, in spite of oscillations of approximate amplitude ±4 steps around the command position, synchronization is maintained.
The effect of operating outside the pull-in characteristic of the motor is shown in figure 4 where a
sequence of 100 steps at a rate of 4000 steps/s is applied to a motor initially at rest. As expected this simulation demonstrates that the open-loop system loses synchronization whereas the closed-loop system settles down to a rotor velocity around 4000 steps/s, and at the end of the step sequence returns to the zero error position.
Finally, figure 5 shows the effect of applying a torque of 0.5 N (which exceeds the peak motor torque) for 10 ms. This causes rapid loss of synchronization in the open-loop system whilst the closed-loop system recovers, even from very large positional errors.
Ideally the recovery from positional error should be asymptotic (that is free from overshoot) but this is far from being the case as can be seen from figures 4 and 5. The control system itself provides no damping and correct operation relies on friction in the motor and load, and on electrical damping provided by the sequencer. In most applications load friction will provide a more rapid approach to rest than that illustrated.
It is probable that a more sophisticated control algorithm could be devised which generated additional damping. For example, the motor speed could be sensed and used in a manner similar to the tachometer in a conventional servomechanism. Unfortunately this would detract from the essential simplicity of the control algorithm described here, and would involve adjustments to suit particular motor/load combinations.