You know the difference between servo drive and stepper drive in woodworking engraving machine

A stepper motor is a discrete motion device that has a physical connection to modern digital control skills. In the current domestic digital control system, the application of stepper motors is very extensive. With the presentation of the all-digital communication servo system, communication servo motors are increasingly used in digital control systems. In order to get used to the development trend of digital control, most of the motion control systems use stepper motors or all-digital communication servo motors as the fulfillment motors. Although the two are similar in control methods (burst and direction signals), there are large differences in the use of functions and applications. The use of the two is now used as a comparison.

First, the control accuracy is different

    The two-phase hybrid stepping motor step angle is generally 3.6 °, 1.8 °, and the five-phase hybrid stepping motor step angle is generally 0.72 °, 0.36 °. There are also some high-performance stepper motors with smaller step angles. For example, a stepping motor for a slow wire-cutting machine produced by Stone Co., Ltd. has a step angle of 0.09°; the three-phase hybrid stepping motor produced by BERGER LAHR can pass the step angle. The DIP switches are set to 1.8°, 0.9°, 0.72°, 0.36°, 0.18°, 0.09°, 0.072°, and 0.036°, and are compatible with the step angle of two-phase and five-phase hybrid stepping motors.

    The control accuracy of the communication servo motor is ensured by the rotary encoder at the rear of the motor shaft. Taking Panasonic's all-digital communication servo motor as an example, for a motor with a standard 2500-line encoder, the pulse equivalent is 360°/10000=0.036° due to the quadruple frequency skill selected inside the driver. For a motor with a 17-bit encoder, the drive receives one revolution per 217 = 131072 pulse motors, ie its pulse equivalent is 360°/131072=9.89 seconds. It is 1/655 of the pulse equivalent of a stepping motor with a step angle of 1.8°.

Second, the low frequency characteristics are different

    Stepper motors are prone to low frequency oscillations at low speeds. The oscillation frequency is related to the load condition and the function of the driver. It is generally considered that the oscillation frequency is half of the take-off frequency of the motor no-load. This low frequency oscillation phenomenon determined by the working principle of the stepping motor is very unfavorable with respect to the normal operation of the machine. When the stepper motor works at low speed, the damping skill should generally be used to defeat the low-frequency oscillation phenomenon, such as adding a damper to the motor or selecting a subdivision skill on the drive.

    The communication servo motor works very smoothly, and it does not exhibit oscillation even at low speeds. The communication servo system has resonance suppression function, which can include the lack of mechanical rigidity, and the system has a frequency analysis function (FFT), which can detect the resonance point of the machine and facilitate system adjustment.

Third, the difference in frequency characteristics

    The output torque of the stepper motor decreases as the speed increases, and it drops sharply at higher speeds, so the maximum operating speed is generally 300 to 600 RPM. The communication servo motor is a constant torque output, that is, it can output additional torque within its extra speed (generally 2000RPM or 3000RPM), and it is a constant power output above the extra speed.

Fourth, the overload can be different

    Stepper motors generally do not have an overload capability. Communication servo motors have strong overload capabilities. Take the Panasonic communication servo system as an example. It has speed overload and torque overload capability. Its maximum torque is three times the extra torque, which can be used to overcome the inertia moment of the inertia load at the moment of launch. Because there is no such overload in the stepping motor, in order to overcome this moment of inertia during the selection, it is often necessary to select a motor with a large torque, and the machine does not require such a large torque during normal operation, and the torque is presented. The phenomenon of dross.

Five, different operating functions

    The operation of the stepping motor is open-loop control. If the starting frequency is too high or the load is too large, it is easy to show the phenomenon of lost or blocked. When the speed is too high, it is easy to overshoot. It is considered that the handling precision should be handled well. The problem of raising and lowering speed. The communication servo drive system is closed-loop control. The driver can directly sample the motor encoder response signal, and internally form the azimuth ring and the speed loop. Generally, the stepping motor is not lost or overshooted, and the control function is more reliable.

Sixth, the speed echo function is different

    The stepper motor needs to be 200 to 400 milliseconds from the stop to the speed of the operation (usually several hundred revolutions per minute). The acceleration of the communication servo system is better. Take the Panasonic MSMA 400W communication servo motor as an example. It takes only a few milliseconds from the stop to accelerate to its extra speed of 3000RPM, which can be used for control situations requiring fast start and stop.

    In summary, the communication servo system is superior to stepper motors in many functions. However, in some occasions where the requirements are not high, the stepping motor is often used to perform the motor. Therefore, in the planning process of the control system, it is necessary to summarize the various factors such as the control requirements and cost, and select the appropriate motor.