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The commutation process of precision surface grinder

Back date: 2020-07-22 10:07:37
Precision surface grinder is a commonly used machine tool for machining. There are higher requirements for smoothness of motion, commutation accuracy, and commutation frequency. At present, surface grinders are developing towards large-scale and high-speed development. The reciprocating speed of some surface grinders' worktables has reached 40 resistance and n[]. The inertia of large-scale high-speed surface grinder is very large. When it changes direction, it will cause the back pressure to rise sharply, which will cause the commutation shock, which will have a catastrophic impact on the machine tool, so the commutation stability problem has become a restriction An important factor in improving the working speed and machining accuracy of a grinder.
  
  The commutation mode and commutation control parameters in the system have a decisive effect on the commutation impact. The surface grinder adopts hydraulic transmission. The design of a new hydraulic reversing system is imminent. The following discusses the reversing impact of the grinder from the perspective of commutation methods and control strategies.
  
   1. The mechanism of commutation shock
  
   Because in its hydraulic system, when the hydraulic drive surface grinder changes direction. The valve port of the reversing valve is instantly closed, and the oil circuit is suddenly disconnected, so that the oil in the oil return cavity cannot be drained.
  
   The larger m and v, it can be seen. The greater the kinetic energy, the greater the commutation impact. For a surface grinder with large inertia and high speed operation, the commutation impact is huge, which not only affects the machining accuracy of the machine tool, but also hinders normal operation and service life.
  
  People all hope that the machine tool can achieve ideal commutation. The so-called ideal commutation means, usually. Under any working conditions, the speed of the machine tool can be smoothly reduced according to an ideal curve without sudden change. The speed is just reduced to zero at the moment the valve is closed, that is, all the kinetic energy is converted into heat energy and is consumed. The ideal commutation process is impactless
  
   2. Analysis of common hydraulic transmission commutation methods
  
   Let's make a simple analysis and comparison. There are many hydraulic drive reversing methods currently applied to surface grinders. >
  
  2.1 Reversing method using stroke reversing valve
  
   A pull rod is connected to the reversing spool, which uses a stroke reversing valve to change direction. Use the stroke stop on the workbench to push the pull rod to realize automatic reversing. When the worktable moves slowly, when the reversing valve reaches the middle position, no matter whether the left and right chambers of the hydraulic cylinder are both filled with pressure oil, or both return oil, or both are closed, at this time, there is no hydraulic pressure in the two chambers of the hydraulic cylinder. Pushing will stop the movement of the workbench, so the reversing valve cannot reach the other end, and the so-called "dead point" appears; in addition, when the workbench moves at a high speed, the stopper pushes the lever to change the direction of the reversing valve very quickly. The pressure of one chamber of the hydraulic cylinder suddenly drops from the working pressure p to 0 and the other chamber suddenly rises from 0 to p, which causes a great reversing shock. At present, this kind of system is widely used on small grinders.
  
  2.2 Reversing method using electromagnetic reversing valve
  
  The travel stop is pushed by the travel switch to send out a reversing signal, and the travel reversing valve is changed to the reversing method of the electromagnetic reversing valve. The solenoid is actuated to push the spool valve to change direction, which can prevent the "dead point". However, it is a switch type hydraulic valve that opens or closes instantaneously according to instructions, that is, instantaneously connects or cuts off the oil return channel. Such a hydraulic reversing system is changing Xiangshi will have a big impact.
  
  2.3 Reversing method using electro-hydraulic reversing valve
  
   Then the main valve is driven by the control oil to change direction. The pilot valve did not change forward, and the electro-hydraulic directional valve replaced the electromagnetic directional valve to constitute a new directional method. The electro-hydraulic directional valve consists of a pilot valve solenoid spool valve and a main valve hydraulic spool valve. This system uses the pilot valve to switch the control oil circuit. The oil flow direction of the control oil circuit does not change, the reversing valve always remains at the original end, the main oil circuit direction does not change, and the workbench can always move forward. Once the control oil circuit switches the direction, the main valve spool moves to another working position according to the preset speed. The main oil circuit changes the direction, and the worktable also reverses movement, preventing the "dead point" of the changeover.
  
  The kinetic energy of such a large inertia worktable can be converted into heat energy and consumed by throttling. The size of the control port of the main valve of the electro-hydraulic directional valve is adjustable, that is, the reversing time △t can be extended. It can effectively reduce the impact of commutation, so this commutation method will dominate for a long time. However, its commutation parameters can only be adjusted in advance, and cannot be changed according to changes in working conditions. For a system whose working conditions change at any time, it is impossible to achieve ideal commutation. Cooperate with ideal control curve. The surface grinder adopts the hydraulic transmission reversing system of electro-hydraulic proportional valve. An intelligent control commutation system is realized by actively reducing the flow rate to reduce the speed, and finally achieving the goal of smooth and impact-free commutation, which can realize the ideal commutation under the change of working conditions. This kind of hydraulic transmission reversing system realizes a good intelligent control of the output displacement or speed, which makes the reversing process have a certain controllability, so it has a very wide range of applications