Stepper Motor in Cllosed Loop Mode

Due to the limitations of open loop contorl, a closed loop control of stepper motors is used in practice. In a closed loop control, the input controller gets the information about the output through the feedback element. Hence the driver circuit receives the control signal which is based on the feedback information. So switching of the motor takes place by means of train of input pulses, which is generated on the basis of feedback from rotor. Such a switching of the motor is called as closed loop mode of operation of the stepper motor. The block diagram shown in the Fig.A.17 illustrates the closed loop operation of the stepper motor.

Let us consider a closed loop temperature control system. The temperature of the tank is required to be kept constant with the help of controlling the steam flow. There exists a valve whose position is controlled by a stepper motor, to control the steam flow. The actual temperature is sensed by using temperature sensor and feedback is given to the input controller. The input contorller has the reference information corresponding to the desired ideal temperature. It compare the feedback with this reference to generate the appropriate contorl signal. This control signal inturn is given to the driver circuit. The driver circuit control the excitation and logical sequence of the excitation of the phases. This drives the stepper motor and hence valve opening gets controlled appropriately so that steam flow gets controlled. This maintains the temperature of the tank constant. The logical operation of the system is illustrated in the block diagram shown in the Fig. A.18.

In a speed and position control systems, optical encoders coupled to the rotor shaft are used. Simlarly use of microprocessors as an input controller for better accuracy is very commen now a days. The Fig. A.19 shows the use of microprocessor in the closed loop control of the stepper motor.

What are the functionalities of these closed-loop stepper systems?

Closed-loop stepper with step-loss compensation will be the most typical kind of closed-loop stepper manage. The stepper drive operates as a micro-stepping drive and usually receives pulse and path commands to move towards the preferred position. An encoder tracks shaft or load position. If lost actions are detected, a compensation algorithm inserts extra actions to ensure that the motor shaft (or load) arrives in the preferred position. Usually, the stepper-motor drive has settings for two currents: The motor gets operating present when in motion and gets resting present when stopped.

In closed-loop stepper with load-position manage, the stepper drive operates as a typical microstepping drive and usually receives pulse and path commands to move towards the preferred position. The encoder (usually mounted around the load) monitors the load's position. The closed-loop algorithm dynamically tracks the load position and compensates all through the move profile. Usually, the motor gets operating present when in motion and gets resting present when stopped.

Closed-loop stepper servo manage treats the stepper motor like a high-pole-count brushless motor, turning it into a servomotor. A shaft-mounted encoder detects shaft position to figure out the correct present vector. A pulse and path interface might be provided within this kind of drive, however the position controller does not use actions to obtain towards the preferred position. Rather, closed-loop algorithms manage motor torque to servo the shaft into position utilizing a position manage loop (a PID loop for instance). Within this mode, the present setting is dynamic. The stepper drive delivers only the quantity of present required to move the motor shaft and load into position.

Types of Steppers

The stepper drive delivers electrical energy towards the motor in response to low-level signals in the manage method. Input signals towards the stepper drive consist of step pulses along with a path signal. 1 step pulse is needed for each step the motor would be to take. This really is accurate no matter the stepping mode. So the drive might need 200 to 101,600 pulses to create 1 revolution from the shaft. Probably the most commonly-used stepping mode in industrial applications will be the half- step mode in which the motor performs 400 actions per revolution. At a shaft speed of 1800 rpm, this corresponds to a step pulse frequency of 20kHz. Exactly the same shaft speed at 25,000 actions per rev demands a step frequency of 750 kHz, so motion controllers controlling microstep drives should be in a position to output a a lot greater step frequency.

You will find a wide selection of stepper kinds, a few of which need extremely specialized drivers. For our purposes, we'll concentrate on stepper motors that may be driven with generally accessible drivers. They are: Permanent Magnet or Hybrid steppers, either 2-phase bipolar, or 4-phase unipolar.

Motor Size

One of the first things to consider is the work that the motor has to do. As you might expect, larger motors are capable of delivering more power. stepper motor drivers come in sizes ranging from smaller than a peanut to big NEMA 57 monsters.

Most motors have torque ratings. This is what you need to look at to decide if the motor has the strength to do what you want.

NEMA 17 is a common size used in 3D printers and smaller CNC mills. Smaller motors find applications in many robotic and animatronic applications. The larger NEMA frames are common in CNC machines and industrial applications.

The NEMA numbers define standard faceplate dimensions for mounting the motor. They do not define the other characteristics of a motor. Two different NEMA 17 motors may have entirely different electrical or mechanical specifications and are not necessarily interchangeable.

Unipolar vs. Bipolar

Unipolar drivers, always energize the phases in the same way. One lead, the "common" lead, will always be negative.  The other lead will always be positive. Unipolar drivers can be implemented with simple transistor circuitry. The disadvantage is that there is less available torque because only half of the coils can be energized at a time.

A two phase bipolar motor has 2 groups of coils. A 4 phase unipolar motor has 4. A 2-phase bipolar motor will have 4 wires - 2 for each phase. Some motors come with flexible wiring that allows you to run the motor as either bipolar or unipolar.

Bipolar Stepper Motor Driver

The Bipolar Stepper Motor Driver additional board is designed to operate bipolar stepper motors in full-, half-, quarter- and eight-step modes. It is available as a stand-alone device or connected to the microcontroller. For connecting the Bipolar Stepper Motor Driver to the microcontroller on the development system, it is necessary to use a flat cable with IDC female connector that should be connected to some development system’s I/O port.

Leadshine's Stepper Motor Driver item line is compatible with most NEMA frame sizes, 08, 11, 15, 17, 23 and 34 stepper motors. Every Stepper Motor Driver series offers numerous various attributes to cover a wide variety of stepper motor/driver applications. These Stepper Motor Drivers are competitively priced, with out sacrificing overall performance or item life. All Leadshine Stepper Motor Drivers are single axis, and variety in the smallest at 0.two Amps to eight.0 Amps (model dependent). Leadshine's complete line of stepper motor drivers consists of step divisors from 400 to 51,200spr, and voltage specifications ranging from 12 - 123VDC (model dependent). All Stepper Motor Drivers provide low voltage and over-voltage protection. Other choices accessible are RS232, RS422, RS485, RS785 and may bus. All Leadshine stepper motor/driver goods are 100% tested for function and reliability.

How to Choose the Stepper Drive

When choosing stepper motor drivers, also known as controllers, several factors must be taken into consideration. Buyers should make sure that the motor is compatible with the driver, as there are several different types. The number of wires in the motor determines whether a bipolar or unipolar driver is required. Maximum current input and output of the motor also impact which driver to buy, as do features such as step modes, step frequency, and protection circuitry.

Step 1:  Select the voltage range

Select an operating voltage range that gives you enough margin to deal with supply pumping (when the motor acts as a generator pumping current into the supply, temporarily raising the voltage) and the various inductive spikes that occur when driving a motor.  The typical rule of thumb for a stepper is to have ~ 20% margin vs. the operating supply voltage of the motor, but depending on the use model of the motor,you may need up to 2x margin, although this is more an extreme case.  For brushed DC and brushless DC motors, it’s more like 1.5x to 2.5x margin. Base your selection on the recommend operating voltage range, not the total voltage.

Step 2: Select the current rating 

Stepper drivers typically drive sinusoidal currents, so consider your peak and RMS current requirements and select a driver that can handle both.  An integrated motor driver’s RMS current rating is a function of thermal performance, I.E. how much current can it handle before shutting down due to the over-temperature protection kicking in.  Typically, the higher the current, the lower the FET RDSON required.   Other variables affecting thermal performance include how efficient the FETs switch and how thermally efficient the package is at getting the heat out.  For a stepper driver, the peak current is typically set at 1.414 of the RMS current.

Step 3: Determine board space and thermal requirements

Integrated motor drivers are your smallest option, but they can’t handle as much current as a pre-driver with external FETs.  Integrated drivers also typically dump the majority of the heat into the board, so if you have a really small board, make sure it can reliably handle the heat. Look for lower RDSON ratings if you are concerned about thermal performance and for high current applications consider a pre-driver with external FETs.

Recommend Leadshine Stepper Drives

Leadshine offers three main series of stepper drives, the advanced digital EM series, digital DM series, and classic M series. The EM series stepper drives are 32-bit DSP-based and adopt Leadshine's latest stepper control technology with many advanced features. The high performance leadshine m542 are featured with extra low noise, very low motor heating, and ultra smooth motor movements at low speed. With performance and costs balanced, Leadshine's M series stepper drives adopt pure sinusoidal control technology & anti resonance, and can offer excellent high speed performance.

Highlights

    2 phase or 3 phase

    20-80 VDC input, or direct 120/230 AC input

    Step & direction control, CW/CCW, or 0-5 DC for speed control

    Capable of driving NEMA 8 to 50 stepper motors

    Digital or analog

    Anti Resonance for excellent performance

    Low cost and high quality

    CE and/or UL/CUL certified

Conclusion

To choose the correct stepper drive, buyers must consider their budget, the intended application of the stepper motor, and the required features. Buyers should ascertain which drives are compatible with the motor in question, since some motors will not work with an incorrect drive. The required features are also important considerations.

Buying a Stepper Motor Driver

When purchasing stepper motor drivers, also called controllers, several factors must be taken into consideration. Buyers should make sure that the motor is compatible with the driver, as there are several different types. The number of wires in the motor determines whether a bipolar or unipolar driver is required. Maximum current input and output of the motor also impact which servo driver to purchase, as do features such as step modes, step frequency, and protection circuitry. There are numerous types of stepper drives available, each with advantages and disadvantages. Choosing the right kind of driver depends on the type of task the stepper motor will be applied to, as well as the step mode requirements. Here recommend you Brand stepper drive by Fasttobuy.com.

The Leadshine Stepper drive's performance comes from its powerful 32-bit DSP processor and associated control algorithms. These achieve smooth performance at low speeds by significantly minimising fluctuations from the desired motor speed. The Leadshine stepper drive can also calculate the natural system frequency and apply a damping function to eliminate resonance. This yields higher speed and better motor performance; it also optimises torque and eliminates mid-range instability. And by cutting stepper motor heating losses, the driver brings energy saving benefits, together with reduced maintenance costs.

System set-up is said to be fast and simple due to the motor auto-tuning and parameter auto-configuration technology. This allows automatic compensation for the unique characteristics of any motor connected to the drive. The motor can be sized from NEMA 17 to NEMA 34 diameter due to wide input voltage coverage and a programmable output current range from 0.5-5.6A. Either two- or four-phase motors can be connected. The drive has a programmable resolution, from full step to 102,400 steps per resolution. The stepper driver's Multistep function allows this full microstepping resolution to be applied to a standard 200-step motor, so system performance becomes smoother.

Highlights

    Suitable to drive size NEMA 17 to NEMA 34 stepper motors
    Supply voltage up to +50VDC
    Programmable output current range from 0.5-5.6A
    Programmable resolution from full step to 102,400 micro steps per resolution
    Support PUL/DIR and CW/CCW modes
    Over-voltage, over-current and phase-error protection provided as standard

Stepper drives always offer the cheapest solution, so use a stepper wherever appropriate. Remember these major considerations: First, does the system require position confirmation? Second: The wrong stepper drive can cause ringing, resonance, and poor low-speed performance. Third, during high speeds, stepper motors can whine. Because stepper drives have a high pole count, hysteresis and eddy current losses are also common at high speed; for these reasons, a stepper is not recommended for continuous operation above 2,000 rpm. Finally, because full current is needed to produce holding torque, step motors can get hot at a standstill.

Fasttobuy has a large selection stepper drives and controls, available in both new and used condition, and the price range varies significantly across the range.