Precision surface grinder is a commonly used machine tool for machining. There are high requirements for motion stability, commutation accuracy and commutation frequency. At present, surface grinding machines are developing towards large-scale and high-speed. The reciprocating speed of some surface grinding machines' workbenches has reached 40% resistant n []. The motion inertia of large high-speed surface grinding machines is very large. When they reverse, it will lead to a sharp rise in back pressure, which will cause reverse impact, which will have a disastrous impact on the machine tool. Therefore, the stability of reverse has become an important factor restricting the improvement of the grinding machine's working speed and processing accuracy.

The reversing mode and reversing control parameters in the system play a decisive role in reversing impact. The surface grinder adopts hydraulic transmission. It is urgent to design a new hydraulic reversing system. Next, from the perspective of reversing method and control strategy, the problem of reversing impact of grinder is discussed.

1. Mechanism of reversing impact

Because in its hydraulic system, when the hydraulic transmission surface grinder reverses. The valve port of the reversing valve is closed instantaneously, and the oil circuit is suddenly disconnected, so that the oil in the oil return chamber cannot be drained.

The greater the m and v, the more you can see. The greater the kinetic energy, the greater the reverse impact. For the surface grinder with large inertia and high-speed operation, its reversing impact is huge, which not only affects the machining accuracy of the machine tool, but also hinders the normal operation and service life.

People hope that the machine tool can realize ideal commutation. The so-called ideal commutation means that, in general. Under any working condition, the speed of the machine tool can be reduced smoothly without sudden change according to an ideal curve. At the moment when the valve is closed, the speed is just reduced to zero, that is, all kinetic energy is converted into heat energy and is consumed. The ideal reversing process is impact free

2. Analysis of Common Hydraulic Transmission Reversing Methods

Here is a simple analysis and comparison. There are many hydraulic drive reversing methods currently applied to surface grinding machines.>

2.1 Reversing method with stroke reversing valve

A pull rod is connected to the reversing valve core to use the stroke reversing valve for reversing. The stroke stop on the workbench is used to push the pull rod to realize automatic reversing. When the worktable moves slowly, when the reversing valve reaches the middle position, whether the left and right chambers of the hydraulic cylinder are filled with pressure oil, or both are filled with return oil, or both are closed, at this time, there is no hydraulic pressure to push the two chambers of the hydraulic cylinder, which will stop the movement of the worktable, so the reversing valve cannot reach the other end, which is the so-called "dead point"; In addition, when the worktable moves at a high speed, the stop pushes the pull rod to change the direction of the reversing valve very quickly, and the pressure in one chamber of the hydraulic cylinder suddenly decreases from the working pressure p to 0, and the pressure in the other chamber suddenly rises from 0 to p, which results in a great reversing impact. At present, this kind of system is widely used in small grinders.

2.2 Reversing method using electromagnetic reversing valve

The travel stop pushes the travel switch to send a reversing signal, and the travel reversing valve is changed to the reversing method of the electromagnetic reversing valve. Making the electromagnet act to push the spool valve to reverse can prevent the "dead point". However, it is a switch type hydraulic valve that can be opened or closed instantaneously according to the command, that is, the oil return channel can be connected or cut off instantaneously. Such a hydraulic reversing system will have a great impact when reversing.

2.3 Reversing method using electro-hydraulic reversing valve

Then the control oil pushes the main valve to reverse. The pilot valve does not shift forward, and a new reversing method is formed by replacing the electromagnetic reversing valve with the electro-hydraulic reversing valve. The electro-hydraulic reversing valve is composed of the solenoid slide valve of the pilot valve and the hydraulic slide valve of the main valve. This system controls the oil circuit by reversing the pilot valve. The oil flow direction of the control oil circuit does not change, the reversing valve is always kept at the original end, the direction of the main oil circuit does not change, and the workbench can always move forward. Once the direction of the control oil circuit is switched, the valve core of the main valve moves to another working position according to the speed set in advance. When the direction of the main oil circuit changes, the workbench also reverses, preventing the "dead point" of the reversing

In this way, the kinetic energy of the large inertia worktable can be converted into heat energy through throttling and consumed. The size of the control oil port of the main valve of the electro-hydraulic reversing valve is adjustable, that is, the reversing time △ t can be extended. The reversing impact can be effectively reduced, so this reversing method is dominant for a long time. However, its reversing parameters can only be set in advance and cannot be changed according to the change of working conditions, which is impossible to achieve ideal reversing for systems whose working conditions change at any time. Match the ideal control curve The surface grinder adopts the hydraulic transmission reversing system of electro-hydraulic proportional valve. It realizes the goal of reducing the speed by actively reducing the flow, and finally achieving a smooth and impact free commutation. An intelligent control type commutation system can also achieve ideal commutation when the working condition changes. This hydraulic drive reversing system realizes a good intelligent control of the output displacement or speed, making the reversing process controllable, so it has a very wide range of applications