Using a screw and nut to mesh, adopting a certain method to prevent relative rotation of the screw and nut, thereby causing axial movement of the screw. Generally speaking, there are currently two ways to achieve this conversion. The first is to embed a rotor with internal threads in the motor, and use the internal threads of the rotor to mesh with the screw to achieve linear motion. The second is to use the screw as the motor output shaft, and use an external drive nut to mesh with the screw outside the motor to achieve linear motion. The result of doing so greatly simplifies the design, allowing for precise linear motion using linear stepper motors in many application fields without installing external mechanical linkage devices. Linear stepper motors are widely used in many high-precision fields, including manufacturing, precision calibration, precision fluid measurement, and precise position movement.

Working principle of screw stepper motor

The rotor of a screw stepper motor is a permanent magnet, and when current flows through the stator winding, the stator winding generates a vector magnetic field. The magnetic field will drive the rotor to rotate by an angle, so that the direction of the rotor's pair of magnetic fields is consistent with that of the stator's magnetic field. When the vector magnetic field of the stator rotates by an angle. The rotor also rotates an angle with the magnetic field. For every input of an electrical pulse, the motor rotates one angle and advances one step. The angular displacement output of the screw stepper motor is proportional to the number of input pulses, and the speed is proportional to the pulse frequency. Changing the order of winding electrification will cause the motor to reverse. So the rotation of the stepper motor can be controlled by controlling the number and frequency of pulses, as well as the sequence of energizing each phase winding of the motor.

Screw stepper motor

The heating principle of screw stepper motors is commonly seen in various types of motors, which have iron cores and winding coils inside. The winding has resistance, and when energized, it will produce losses. The magnitude of the losses is proportional to the square of the resistance and current, which is commonly known as copper losses. If the current is not a standard DC or sine wave, harmonic losses will also occur; The iron core has hysteresis eddy current effect, which can also cause losses in alternating magnetic fields. The magnitude of these losses is related to the material, current, frequency, and voltage, which is called iron loss. Copper and iron losses will both manifest in the form of heat, thereby affecting the efficiency of the motor. Screw stepper motors generally pursue positioning accuracy and torque output, with relatively low efficiency, high current, and high harmonic components. The frequency of current alternation also varies with the speed, so stepper motors generally have heating problems, which are more severe than general AC motors.

The purpose of the screw stepper motor

1. When the screw stepper motor is working, each phase winding is not constantly energized, but alternately energized according to a certain rule.

2. The angle at which the rotor rotates with each input pulse electrical signal is called the step angle.

3. The screw stepper motor can be controlled for angle and speed according to specific instructions. When controlling the angle, for each input pulse, the stator winding is switched once, and the output shaft rotates through an angle with the same number of steps as the number of pulses. The angular displacement of the output shaft rotation is proportional to the input pulse. When controlling the speed, continuous pulses are fed into the winding of the stepper motor, and the windings of each phase are continuously energized. The stepper motor rotates continuously, and its speed is proportional to the pulse frequency. By changing the power on sequence, that is, by changing the direction of rotation of the stator magnetic field, the motor can be controlled to rotate forward or backward.

4. The screw stepper motor has self-locking capability. When the control pulse stops inputting and the winding controlled by the last pulse continues to be powered by DC, the motor can remain in a fixed position, that is, at the end position of the angular displacement controlled by the last pulse. In this way, the stepper motor can achieve rotor positioning when stopping.

Linear module supplier _ Selection of three-axis simple robotic arm _ Which is good for multi axis linear sliding table

The linear module screw type can be repeatedly positioned, aiming to accurately record accuracy and achieve movement effect. Next, let's take a look at the accuracy requirements for repeated positioning. The repeatability of a positioning system refers to the degree of change in the actual positioning position when attempting to continuously pass through a specific location. A system with high repeatability (accuracy may or may not be high) exhibits very low positional dispersion when repeatedly passing through the same given position, regardless of direction. The difference between moving towards a point in the same direction (single directional repeatability) and moving towards a point in the opposite direction (bidirectional repeatability). Generally speaking, the position change of bidirectional movement is higher than that of unidirectional movement. Only looking at the repeatability data of one-way movement alone will not reveal significant influences on gear backlash.

If high repeatability is required, it is best not to use lead screws and instead use linear motors as carried out components. Although this requires the use of linear encoders and the slider and servo controller to operate in closed-loop mode, the resulting performance will be greatly improved, and the limitations only come from the resolution of the encoder and the inevitable thermal effects.

Although the above approach of eliminating the impact of thermal effects on measurement repeatability is too accurate, our purpose in doing so is to fully demonstrate the high internal repeatability characteristics of our anti backlash nut (used together with the slide driven by the lead screw) design. A large number of tests conducted using laser interferometers have shown that typical unidirectional values are below 0.05 millimeters (while many other products range from 0.01 to 0.02 millimeters), and bidirectional values are below ± 0.01-0.02 millimeters (while many other products range from 0.02 to 0.05 millimeters). In addition, the anti backlash nut design also has self compensating characteristics, and even after long-term use, the repeatability value of the equipment will not decrease by more than 0.05 millimeters. As can be seen from the above, the linear module screw type has very strict requirements for the accuracy of repeated positioning, and the higher the accuracy, the more guaranteed the quality of the product.