Why does the CNC high-precision centerless grinder appear "backward drag"? How to deal with it?
The CNC high-precision centerless grinder is a machine tool that uses abrasive tools to grind the surface of the workpiece. Most grinders use high-speed rotating grinding wheels for grinding, and a few use other grinding tools such as oilstone, abrasive belts and free abrasives for grinding. It can realize online active measurement, adaptive control of grinding and dressing, and has the function of anti-collision. It provides solutions for machine tools, grinding wheels, rolls and grinding processes, and optimizes the configuration of the process system according to the characteristics of different workpieces, so that the grinding performance reaches the ideal effect, and it realizes fully automatic in-line machining and meets the requirements of high efficiency and high precision. High precision.
The feed rail of the CNC high-precision centerless grinder is a plastic or rolling rail that is sensitive to movement. The feed system is driven by a servo motor and a ball screw nut to achieve precise feed (one grinding can be divided into rapid step, rough grinding, fine grinding, delay and other steps, and the feed amount and speed of each step can be set arbitrarily ), the feed repeat positioning accuracy is within 0.002mm. The compensation of the finishing mill is also driven by a servo motor ball screw nut, with a repeat positioning accuracy of 0.001mm. Therefore, the feed system can simultaneously compensate the trimming amount after trimming, so that the size of the workpiece after trimming remains stable. The electrical system also uses the touch screen as the numerical control system. Various grinding parameters and dressing parameters can be set on the screen. The operation is simple and clear to realize the automatic grinding of the machine tool. Automatic dressing improves the quality of grinding, improves the efficiency of the machine tool, realizes one person with multiple machines, and greatly improves the overall efficiency. At the same time, the CNC high-precision centerless grinder has a self-diagnostic function and is easy to maintain.
Due to the small diameter of the processed parts, the speed of the guide wheel is required to be relatively low, thereby reducing the output voltage and load capacity of the thyristor device. In actual production, due to the over-tolerance of the blank or other reasons, the grinding amount per unit time increases. The grinding force generated by grinding the workpiece with the grinding wheel will change the speed of the guide wheel, which is called "back drag".
In order to eliminate the influence of "back drag", the machine tool factory specially designed a loading device, requiring additional parts on the CNC high-precision centerless grinder, and the structure became complicated. From the above analysis, it can be seen that the motor is in the generator running state when it is "reversed". If the working principle of the reversible system is adopted, a current channel is provided to reverse the armature current at this time. Then, when the speed is higher than a given speed (refers to the guide motor speed during normal grinding, usually when the diameter of the grinding part is less than 25mm, the motor speed is less than 50r/min), the motor can be braked to achieve the purpose of stabilizing the speed. Using the method of paralleling the armature at both ends of the DC motor, when the stator speed is higher than the given speed, it provides braking current for the motor in the generator state, limiting the speed increase, and effectively eliminating the influence of the motor being "pulled backward" , And keep the speed basically stable. In addition, we connect switches in series in the resistance loop to ensure that the resistance is only turned on during low-speed grinding of the guide wheel to prevent the resistance from consuming energy at other times.
This measure can not only keep the rotation speed of the guide wheel stable, but also improve the processing capacity of the CNC high-precision centerless grinder (increase the grinding amount). Therefore, this method can be used to eliminate the "reverse resistance" when the DC motor is running at low speed.