A surface grinder is a commonly used machine tool for mechanical processing. There are high requirements for motion stability, commutation accuracy, and commutation frequency. The motion inertia of large high-speed surface grinders is very large. When they change direction, it will cause a sharp increase in back pressure, resulting in a reversal impact, which will have a catastrophic impact on the machine tool. Therefore, the problem of smooth reversal has become an important factor restricting the improvement of grinding machine working speed and machining accuracy. There are many hydraulic transmission reversing methods currently applied to surface grinders. Based on the analysis of commonly used hydraulic transmission reversing methods, a simple comparison and analysis will be made below.

The method of reversing using a stroke reversing valve
A pull rod is connected to the reversing valve core to use a stroke reversing valve for reversing. Use the travel stop on the workbench to push the pull rod to achieve automatic direction change. When the worktable moves slowly, when the directional valve reaches the middle position, whether the left and right chambers of the hydraulic cylinder are both filled with pressure oil, or both chambers are filled with return oil, or both chambers are closed, at this time, there is no hydraulic pressure pushing the two chambers of the hydraulic cylinder, which will stop the worktable movement. Therefore, the directional valve cannot reach the other end, and the so-called "dead point" occurs; When the worktable moves at high speed, the stopper pushes the pull rod to change the direction of the directional valve very quickly. The pressure in one chamber of the hydraulic cylinder suddenly drops from the working pressure p to 0, and the pressure in the other chamber suddenly rises from 0 to p, resulting in a significant directional shock. At present, this system is widely used in small grinding machines.

Switching method using electromagnetic directional valve
The travel switch is driven by the travel block to send a direction change signal, and the direction change valve is changed to an electromagnetic direction change valve. Making the electromagnet move to push the slide valve to change direction can prevent "dead spots", but it is a switch type hydraulic valve that opens or closes instantly according to instructions, that is, instantly connects or cuts off the return oil channel. Such a hydraulic reversing system will have a significant impact during reversing.

Switching method using electro-hydraulic directional valve
Then, the control oil drives the main valve to change direction. The pilot valve did not switch forward, and replacing the electromagnetic directional valve with an electro-hydraulic directional valve constitutes a new directional method. The electro-hydraulic directional valve consists of a pilot valve solenoid spool and a main valve hydraulic spool. This system controls the oil circuit by reversing the direction of the pilot valve. The direction of oil flow in the control oil circuit does not change, the directional valve always remains at the original end, the direction of the main oil circuit does not change, and the worktable can always continue to move forward.
Cooperate with the ideal control curve. The surface grinder adopts a hydraulic transmission reversing system with an electro-hydraulic proportional valve. An intelligent control type reversing system has achieved the goal of smooth and impact free reversing by actively reducing flow rate to reduce speed. It can also achieve ideal reversing under changing working conditions. This hydraulic transmission reversing system achieves good intelligent control of output displacement or speed, making the reversing process controllable to a certain extent, and therefore has a very wide range of applications.