The basic method of driving a stepper motor is a single excitation mode. It is an old method and not used much at present but one has to know about this technique. In this technique every phase otherwise stator next to each other will be triggered one by one alternatively with a special circuit. This will magnetize & demagnetize the stator to move the rotor forward.

The steps for each resolution can be defined as the number of step angles necessary for a total revolution. The formula for this is 360°/Step Angle.

Field of view diaphragmGenerally, a microscope has a field of view besides the aperture stop. Relative to the light source, its position is behind the aperture stop. Adjusting the field diaphragm can change the size of the microscope field of view without affecting the resolution of the objective lens. Proper adjustment of the field diaphragm can also reduce the reflection and glare in the lens barrel and improve the contrast and quality of imaging. However, it should be noted that if the field diaphragm is too small, the observation range will be too narrow, and it should generally be adjusted to the same size as the eyepiece field.

The above two kinds of objective lenses are classified according to the correction degree of spherical aberration and chromatic aberration. The horizontal field objective lens is based on the breadth of field of view plane correction. The head-up field objective lens can correct the curvature of the image field well. The flat-field objective lens can be divided into flat-field achromatic objective lens and apochromatic objective lens, and the correction of spherical aberration and chromatic aberration is the same as that of achromatic objective lens and apochromatic objective lens respectively. The characteristic of this kind of objective lens is that it significantly expands the flat range of the image field, making the whole field of view clearer, suitable for observation and more conducive to photography.

The stepper motors are generally two-phase motors like unipolar otherwise bipolar. For each phase in a unipolar motor, there are two windings. Here, center-tapped is a common one lead in between two windings toward a pole. The unipolar motor has 5 to 8 leads.

On reset, Q1 of IC3 goes ‘high’ while all other Q outputs go ‘low’. An external reset can be activated by pressing the reset switch. By pressing the reset switch, you can stop the stepper motor. The motor again starts rotating in the same direction by releasing the reset switch.

Stepper motors operate differently from DC brush motors, which rotate when voltage is applied to their terminals. Stepper motors, on the other hand, effectively have multiple toothed electromagnets arranged around a central gear-shaped piece of iron. The electromagnets are energized by an external control circuit, for example, a microcontroller.

This microcontroller doesn’t supply sufficient current to drive the coils so the current driver IC likes ULN2003A. ULN2003A must be used and it is the collection of 7- pairs of NPN Darlington transistors. The designing of the Darlington pair can be done through two bipolar transistors which are connected for achieving maximum current amplification.

A stepper motor is an electromechanical device it converts electrical power into mechanical power. Also, it is a brushless, synchronous electric motor that can divide a full rotation into an expansive number of steps. The motor’s position can be controlled accurately without any feedback mechanism, as long as the motor is carefully sized to the application. Stepper motors are similar to switched reluctance motors. The stepper motor uses the theory of operation for magnets to make the motor shaft turn a precise distance when a pulse of electricity is provided. The stator has eight poles, and the rotor has six poles. The rotor will require 24 pulses of electricity to move the 24 steps to make one complete revolution. Another way to say this is that the rotor will move precisely 15° for each pulse of electricity that the motor receives.

Thus, this is all about an overview of the stepper motor like construction, working principle, differences, advantages, disadvantages, and its applications. Now you have got an idea about the types of super motors and their applications if you have any queries on this topic or the electrical and electronic projects leave the comments below.

The main reason is, once the motor is rotating, its input electrical power part can be changed to mechanical power. When the motor is stopped while it is rotating, then all input power can be changed into heat on the inside of the coil.

The stepper motor working principle is Electro-Magnetism. It includes a rotor which is made with a permanent magnet whereas a stator is with electromagnets. Once the supply is provided to the winding of the stator then the magnetic field will be developed within the stator. Now rotor in the motor will start to move with the rotating magnetic field of the stator. So this is the fundamental working principle of this motor.

The construction of a stepper motor is fairly related to a DC motor. It includes a permanent magnet like Rotor which is in the middle & it will turn once force acts on it. This rotor is enclosed through a no. of the stator which is wound through a magnetic coil all over it. The stator is arranged near to rotor so that magnetic fields within the stators can control the movement of the rotor.

This technique is most frequently used due to its accuracy. The variable step current will supply by the stepper motor driver circuit toward stator coils within the form of a sinusoidal waveform. The accuracy of every step can be enhanced by this small step current. This technique is extensively used because it provides high accuracy as well as decreases operating noise to a large extent.

The motor’s arrangement can be decided through the step-angle & it is expressed within degrees. The resolution of a motor (the step number) is the no. of steps which make within a single revolution of the rotor. When the step-angle of the motor is small then the resolution is high for the arrangement of this motor.

Before selecting a stepper motor for your requirement, it is very significant to examine the torque-speed curve of the motor. So this information is available from the designer of the motor, and it is a graphical symbol of the torque of the motor at a specified speed. The motor’s torque-speed curve should match closely the necessities of the application; or else, the expected system performance cannot be obtained.

Alternatively, stepper motors are designed to make a discrete step, then wait there; again step and stay there. If we want to make the motor stay in a single location for less time before stepping again then it will look like rotating continuously. The power consumption of these motors is high but the power dissipation mainly occurs once the motor is stopped or designed poorly then there is a chance for overheating. Because of this reason, the motor’s current supply is frequently decreased once the motor is in a holding position for a longer time.

In that way, the motor can be turned by a precise. Stepper motor doesn’t rotate continuously, they rotate in steps. There are 4 coils with a 90o angle between each other fixed on the stator. The stepper motor connections are determined by the way the coils are interconnected. In a stepper motor, the coils are not connected. The motor has a 90o rotation step with the coils being energized in a cyclic order, determining the shaft rotation direction.

The higher the magnification of the objective lens, the shorter the working distance! Therefore, it is necessary to be extra careful when observing the focusing, and generally, the objective lens should run in the direction away from the object.

Stepper motor driving techniques can be possible with some special circuits due to their complex design. There are several methods to drive this motor, some of them are discussed below by taking an example of a four-phase stepper motor.

Stepper motor interfacing with 8051 is very simple by using three modes like wave drive, full step drive & half step drive by giving the 0 & 1 to the motor’s four wires based on which drive mode we have to choose for running this motor.

To make the motor shaft turn, first one electromagnet is given power, which makes the gear’s teeth magnetically attracted to the electromagnet’s teeth. At the point when the gear’s teeth are thus aligned to the first electromagnet, they are slightly offset from the next electromagnet. So when the next electromagnet is turned ON and the first is turned OFF, the gear rotates slightly to align with the next one and from there the process is repeated. Each of those slight rotations is called a step, with an integer number of steps making a full rotation.

diaphragmThere are two diaphragms in the illumination system of metallographic microscope, namely aperture diaphragm and field diaphragm.

In this technique, two stators are activated at a time instead of one in a very less time period. This technique results in high torque & allows the motor to drive the high load.

The step angle of the stepper motor can be defined as the angle at which the motor’s rotor turns once a single pulse is given to the stator’s input. The resolution of the motor can be defined as the number of steps of the motor and the number of revolutions of the rotor.

Apochromatic objective lensApochromatic objective lens is a high quality objective lens, which can correct the chromatic aberration in three wave regions (actually equal to the whole visible light range). Spherical aberration correction can reach the range of green and purple light, but it has no fundamental improvement on image domain bending. This kind of objective lens has no restrictions on the light source, and generally has a large numerical aperture and high imaging quality, which is suitable for high-magnification observation.

The remaining two wires must be coupled to a voltage supply. Here the unipolar stepper motor is used where the four ends of the coils are connected to the primary four pins of port-2 in the microcontroller using the ULN2003A.

In ULN2003A driver IC, input pins are 7, output pins are 7, where two pins are for power supply & Ground terminals. Here 4-input & 4-output pins are used. As an alternative to ULN2003A, L293D IC is also used for amplification of current.

Thus, logic 1 output keeps shifting circularly with every clock pulse. Q outputs of all the four flip-flops are amplified by Darling-ton transistor arrays inside ULN2003 (U2) and connected to the stepper motor windings orange, brown, yellow, black to 16, 15,14, 13 of ULN2003 and the red to +ve supply.

Servo motors are suitable for high torque & speed applications whereas the stepper motor is less expensive so they are used where the high holding torque, acceleration with low-to-medium, the open otherwise closed-loop operation flexibility is required. The difference between the stepper motor and servo motor includes the following.

This is the most common type of stepper motor as compared with different types of stepper motors available in the market. This motor includes permanent magnets in the construction of the motor. This kind of motor is also known as tin-can/can-stack motor. The main benefit of this stepper motor is less manufacturing cost. For every revolution, it has 48-24 steps.

Field of viewmicroscope

In the construction, where the common of two poles are divided however center-tapped, this stepper motor includes six leads. If the two-pole center taps are short inside, then this motor includes five leads. Unipolar with 8 leads will facilitate both series & parallel connection while the motor with five lead or six lead has stator coil’s series connection. The operation of the unipolar motor can be simplified because while operating them, there is no requirement of reversing the flow of current within the driving circuit which are known as bifilar motors.

Stepper motor control circuit is a simple and low-cost circuit, mainly used in low power applications. The circuit is shown in the figure, which consists of 555 timers IC as a stable multi-vibrator. The frequency is calculated by using the given relationship.

Variable reluctance (VR) motors have a plain iron rotor and operate based on the principle that minimum reluctance occurs with minimum gap, hence the rotor points are attracted toward the stator magnet poles.

The stepper motor can be controlled by energizing every stator one by one. So the stator will magnetize & works like an electromagnetic pole which uses repulsive energy on the rotor to move forward. The stator’s alternative magnetizing as well as demagnetizing will shift the rotor gradually &allows it to turn through great control.

The exactness of the arrangements of the objects through this motor mainly depends on the resolution. Once the resolution is high then the accuracy will be low.

Permanent magnet motors use a permanent magnet (PM) in the rotor and operate on the attraction or repulsion between the rotor PM and the stator electromagnets.

Aperture diaphragmAperture diaphragm is used to control the thickness of incident light beam, and its position is close to the light source. Generally, the aperture diaphragm of a microscope can be continuously adjusted. When the aperture diaphragm is reduced, the beam entering the objective lens becomes thinner, and the light does not pass through the edge of the objective lens group, so the spherical aberration is greatly reduced. However, the beam thinning will reduce the aperture angle of Wu Jingdi, which will reduce the actual numerical aperture and resolution. When the aperture diaphragm is enlarged, the incident beam becomes thicker and the aperture angle of the objective lens increases, which can make the light fill the rear lens of the objective lens. At this time, the numerical aperture can reach the rated value and the resolution is improved. However, due to the increase of spherical aberration and the increase of internal reflection and glare in the lens barrel, the imaging quality will be reduced. Therefore, the aperture diaphragm has a great influence on the imaging quality, and it must be properly adjusted when it is used. It should not be too large or too small, and its appropriate degree should be based on the lens after the light beam fills the objective lens, and judged according to the clarity of the imaging. After replacing the objective lens, the aperture stop must be adjusted properly. But it is not used to adjust the brightness of the field of view.

Hybrid stepper motors are named because they use a combination of permanent magnet (PM) and variable reluctance (VR) techniques to achieve maximum power in small package sizes.

In a bipolar stepper motor, for each pole, there is a single winding. The direction of supply needs to change through the driving circuit so that it will become complex so these motors are called unifilar motors.

The most popular type of motor is the hybrid stepper motor because it gives a good performance as compared with a permanent magnet rotor in terms of speed, step resolution, and holding torque. But, this type of stepper motor is expensive as compared with permanent magnet stepper motors. This motor combines the features of both the permanent magnet and variable reluctance stepper motors. These motors are used where less stepping angle is required like 1.5, 1.8 & 2.5 degrees.

The stepper motor like variable reluctance is the basic type of motor and it is used for the past many years. As the name suggests, the rotor’s angular position mainly depends on the magnetic circuit’s reluctance that can be formed among the teeth of the stator as well as a rotor.

Parfocal length

achromatic objectiveThe correction of spherical aberration by achromatic objective lens is limited to yellow and green light, and only red and green light are corrected for chromatic aberration. Therefore, the achromatic objective still has residual chromatic aberration, and the image domain curvature still exists. When using achromatic objective lens, yellow-green light or yellow-green color filter can reduce aberration.

According to the different degrees of aberration correction, objective lenses are generally divided into achromatic objective lenses, apochromatic objective lenses and flat-field objective lenses.

Some accuracy motors can create 1000 steps within a single revolution including 0.36 degrees of step-angle. A typical motor includes 1.8 degrees of step angle with 200 steps for each revolution. The different step angles such as 15 degrees, 45 degrees, and 90 degrees are very common in normal motors. The number of angles can change from two to six and a small step angle can be attained through slotted pole parts.

The working of this motor is shown by operating the switch. The coils are activated in series in 1-sec intervals. The shaft rotates 90o each time the next coil is activated. Its low-speed torque will vary directly with current.

The RPM is the revolution per minute. It is used to measure the frequency of revolution. So by using this parameter, we can calculate the number of revolutions in a single minute. The main relation between the parameters of the stepper motor is like the following.

You need to observe two common wires & four coil wires very carefully or else the stepper motor will not turn. This can be observed by measuring the resistance through a multimeter but the multimeter won’t display any readings among the two phases of wires. Once the common wire & other two wires are in the equal phase then it must show a similar resistance whereas the two coils finish points in the similar phase will demonstrate the double resistance as compared with resistance among common point as well as one endpoint.

The output of the timer is used as a clock for two 7474 dual ‘D’ flip-flops (U4 and U3) configured as a ring counter. When power is initially switched on, only the first flip-flop is set (i.e. Q output at pin 5 of U3 will be at logic ‘1’) and the other three flip-flops are reset (i.e. the output of Q is at logic 0). On receipt of a clock pulse, the logic ‘1’ output of the first flip-flop gets shifted to the second flip-flop (pin 9 of U3).

The common point of the winding is connected to the +12V DC supply, which is also connected to pin 9 of ULN2003. The color code used for the windings is may vary from make to make. When the power is switched on, the control signal connected to the SET pin of the first flip-flop and CLR pins of the other three flip-flops goes active ‘low’ (because of the power-on-reset circuit formed by the R1-C1 combination) to set the first flip-flop and reset the remaining three flip-flops.

The field of view refers to the size of the surface area of the sample observed in the microscope. The field of view is inversely proportional to the magnification of the objective lens. Generally, the diameter of the first magnified real image of an ordinary objective lens is 18mm, and the diameters of the field of view of an objective lens with magnification of 10x, 40x and 100x are 1.8 mm, 0.45mm and 0.18mm respectively. The diameter of the first enlarged real image of the head-up field objective lens can reach 28mm, and the market scope is greatly increased.

Generally, all the motors run or rotate continuously but most of the motors cannot stop while they under power, When you try to restrict the shaft of a motor when it is under power supply then it will burn or break.

The working distance of the objective lens refers to the distance between the sample surface and the front end of the objective lens after the microscope is accurately focused.

In this motor, there is a soft iron that is enclosed through the electromagnetic stators. The poles of the stator as well as the rotor don’t depend on the kind of stepper. Once the stators of this motor are energized then the rotor will rotate to line up itself with the stator otherwise turns to have the least gap through the stator. In this way, the stators are activated in a series to revolve the stepper motor.

Both the stepper and dc motors are used in different industrial applications but the main differences between these two motors are a little bit confusing. Here, we are listing some common characteristics between these two designs. Each characteristic is discussed below.

This technique is fairly related to the Full step drive because the two stators will be arranged next to each other so that it will be activated first whereas the third one will be activated after that. This kind of cycle for switching two stators first &after that third stator will drive the motor. This technique will result in improved resolution of the stepper motor while decreasing the torque.