The use of stepper motors and their control systems in bearing grinders in our country began in the 1990s. Over the past two decades, the adoption of stepper motor control technology in bearing grinders has grown rapidly. Today, manufacturers in cities such as Wuxi, Shijiazhuang, Chengdu, and several places in Henan are mass-producing bearing grinders that use stepper motor control systems. With a large number of these machines entering the market, issues related to the stability and accuracy of the stepper motor control system have become increasingly apparent.
While single-axis systems tend to be relatively stable, multi-axis systems often face problems such as lack of synchronization, inconsistent positioning, and instability. In our analysis of a ball bearing groove grinder, we tested several brands of stepper motors and found significant synchronization issues between the two axes. We conducted error tests starting from the PLC, position control modules, motor drivers, and the motors themselves.
With a lead of 4mm on the ball screw and a harmonic reducer with a reduction ratio of 1:80, the step angle of the motor was 0.9 degrees. The resulting positioning error exceeded the machine tool's inspection standards by three times. According to a pulse equivalent of 0.125 micrometers, the total positioning error reached 0.003 after 20 cycles. As shown in Table 1, not only is the stepping motor's error significant, but the mechanical system's errors are even more pronounced.
We analyzed the feeding mechanism and compensation system and found serious mechanical issues. First, the ball screw had a small nominal diameter (Φ20) and low precision level (grade 3), leading to noticeable crawling. Second, the feed cylinder and ball screw were improperly aligned during assembly, causing persistent positioning errors. Third, the harmonic reducer and ball screw were connected without keys or pins, reducing stability. Finally, the system did not use ball screw bearings, further compromising performance.
We also examined the electrical system and found several issues, including poor layout of components such as frequency converters, transformers, and motor controllers placed too close together. The data cables from the PLC were unshielded, and there was mixing of high- and low-voltage cables. These design flaws significantly affect the system’s anti-interference capability, leading to unpredictable errors in both the feeding and compensation systems.
Combined with the mechanical system’s inherent inaccuracies, the machine becomes unstable during operation. Although replacing the hydraulic feed compensation system with a stepper motor system improves overall performance—eliminating hydraulic fluctuations and mechanical transmission errors—the system still requires careful design updates to meet modern demands.
Stepper motors allow for staged feed control, with different pulse frequencies used to adjust speed and precise pulse counting to control table movement. Compared to traditional hydraulic systems, this is a major advancement. However, other parts of the machine must also be upgraded to match the new control system’s requirements.
Whether it's the mechanical structure or the electrical system, the limited anti-interference capability of the stepper motor system should not be overlooked. If these issues are not properly addressed, the machine may not achieve the expected improvements in performance.
In fact, the most effective solution is to adopt advanced servo motor control systems. Servo-driven bearing grinders eliminate the need for fast cylinders and harmonic reducers, using direct-coupled ball screws and servo motors to minimize mechanical errors. Although many Chinese manufacturers still use pulse-controlled servo systems, they offer far better driving capability, interference resistance, and repeat positioning accuracy compared to stepper motor systems.
Due to its limitations and bugs, the stepper motor system is essentially a transitional technology between hydraulic and full servo control. Few countries today use precision motor-controlled stepper systems for grinding, while China has been using them in CNC machines for the longest time.
As the Chinese bearing industry accelerates technological innovation and more high-quality enterprises emerge, it is only a matter of time before stepper motor-controlled bearing grinders are replaced by servo motor systems.
Full Electric Stackers(Walkie Type)
Full electric stackers, also known as walkie stackers, are powered material handling equipment used for lifting and transporting pallets and loads within a warehouse or industrial setting. Unlike traditional forklifts, full electric stackers do not require a dedicated operator seat and are operated by a pedestrian walking alongside or behind the equipment.
These stackers are powered by electric motors and are equipped with a battery that provides the necessary power to lift and move loads. They are designed to be compact and maneuverable, making them ideal for use in narrow aisles and tight spaces.
Full electric stackers typically have a lifting capacity ranging from 1,000 to 3,000 pounds, although some models can handle heavier loads. They are equipped with forks or platforms that can be raised and lowered to lift and stack pallets or other loads. Some models also feature adjustable forks or platforms to accommodate different load sizes.
These stackers are designed with safety features such as brakes, emergency stop buttons, and load backrests to prevent accidents and ensure the safe handling of loads. They also often come with features like adjustable steering handles, easy-to-use controls, and ergonomic designs to enhance operator comfort and efficiency.
Full electric stackers offer several advantages over other types of material handling equipment. They are quieter and produce zero emissions, making them suitable for indoor use and environmentally friendly. They also require less maintenance compared to internal combustion-powered equipment, reducing downtime and operating costs.
Overall, full electric stackers are versatile and efficient tools for lifting and moving loads in warehouses, distribution centers, and other industrial settings. They provide a cost-effective and environmentally friendly solution for material handling needs.
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