Because of its good flexibility, the horizontal machining center is easy to compose a flexible processing automatic line and becomes the preferred equipment master machine of the current manufacturer. Among them, the machining center with double pallet exchange device is the most widely used, and its equipped double worktable saves time and effort for workpiece clamping and disassembly. Since the pallet exchange device needs to be lifted before it is rotated, the conventional design in the past is to lift the device by directly using a cylinder without a self-locking function, and it is only safe and stable under slow running conditions. The impact is enormous and unreliable. Figure 1 Lift the main view of the mechanism The specific movement process of the lifting mechanism is as follows: the driving cylinder 1 pushes the moving cam 2 to move forward, the working cam profile of the moving cam pushes the support roller 3 to perform vertical movement, and the supporting roller drives the push rod 4 to perform vertical movement through the pin shaft. It is shown that the moving cam has moved to the end position while the push rod reaches the highest point. Figure 2 Moving cam profile The second vertical stroke is 12.5mm, and the level stroke is 48mm. It consists of two parabola lines and is connected to the next rising line. The push rod first accelerates 5.48m and then decelerates 7.02m. Raise the device near the pallet and latch. Table movement cam profile characteristic table (t: instantaneous time per curve function) 3. The push rod performs uniform acceleration and uniform deceleration in the four-parabolic section. The acceleration is constant, the impact is minimal, and the operation is smooth. The movement of the putter's movement speed v and acceleration a with the movement time t is shown in Fig. 3. Fig. 3 Diagram of the speed and acceleration of the putter over time Conclusion Zw Self-Primg Sewage Pump,Zw Series Self-Priming Sewage Pump,Diesel Engine Mobile Sewage Pump,Zw Series Self Priming Sewage Pump Lanco Fluid Technology Co.,Ltd , https://www.cnlcpump.com
For this reason, in the development of high-speed machining centers, in order to shorten the lifting time of the pallet exchange device, a quick lifting mechanism is designed, which has a strong carrying capacity, a small impact force, a simple structure, and a real quick lifting.
working principle
The quick lifting mechanism of the double pallet exchange device in the high-speed machining center drives the moving cam with the cylinder as the power, accurately realizing the quick, steady, no impact and low noise of the lifting device during the whole lift operation. The contour curve of the cam is connected by two straight lines, one oblique line and four parabolic lines. The profile curve of the acceleration and deceleration cams is designed as a parabola, and the parabola acceleration is a constant, which minimizes the impact when the lifting mechanism shifts.
During the lifting of the pallets, in order to reduce the working time, the lifting mechanism must be operated quickly. When lifting, to reduce the impact force and noise generated by the lifting device at the moment of activation, contact with the pallet, and the moment when the stroke reaches the end point, it is necessary to reduce the operating speed of these moments.
Therefore, the speed of the lifting mechanism during the entire movement cannot be constant, but changes, while taking into account that the higher the rate of change (acceleration) is, the greater the impact force is, and a characteristic that can adapt to the speed change and have good performance must be designed. Curve, in order to achieve the speed and smooth movement of the lifting mechanism.
This structure takes the moving cam as the main component. The contour curve of the cam is formed by two straight lines, a diagonal line and four parabolic lines. Using the curved structure of the moving cam to achieve continuous lift, from zero speed - acceleration - uniform - deceleration - uniform - acceleration - uniform - deceleration - zero speed. In the speed change interval, the cam profile is parabolic, and the parabolic motion acceleration is a constant, which greatly reduces the rate of change of the speed and reduces the impact, so that the movement is stable and reliable.
Mechanical structure
The mechanical structure of the mechanism for quickly lifting the mechanism is shown in Fig. 1. The mechanism mainly includes four parts: a driving cylinder, a moving cam, a supporting roller, and a push rod. 
Work process analysis
The pallet changer of the high-speed machining center must lift the pallet quickly before turning. The weight of the two pallets and the jig on the pallet is about 4 tons, and the pallet exchange device itself weighs about 1 ton.
The entire lifting process is as follows: Lift the device Accelerate to lift Fast access to the pallet - Slow contact with the pallet and lift the pallet - Accelerate lifting the pallet - Near the end of the deceleration - Enter the load-bearing state. The push rod lifts the stroke 50mm, requiring a time of 0.8 seconds.
1. Allocation of motion trajectories
The first vertical stroke 0mm, level stroke 5mm, consists of a straight line. 
The third vertical stroke of 5mm, the level of travel 80mm, composed of a straight line, slow uniform movement, the completion of the pallet exchange device slowly contact the pallet (the completion of the bolt) and ready to lift the pallet.
The fourth paragraph of the vertical stroke of 32.5mm, the level of travel 112mm, composed of two parabolic lines, and the next level of the line of kiss. First speed up the pallet 18.288mm and then decelerate 14.212mm to reach the end.
The fifth paragraph vertical stroke 0mm, level stroke 5mm, composed of a straight line, the pallet exchange device does not move vertically into the load-bearing state. The above working process analysis is shown in Figure 2.
2. Parameters
The level stroke of the drive cylinder 1 is 250mm, the speed is a constant (0.3125m/s), and the time is 0.8s. The list of the movement speed, acceleration and time of the pushrod in each section is shown in the table below. 
In recent years, with the rapid development of domestic processing and manufacturing industries, agile, flexible, and efficient manufacturing systems have increasingly been widely used, not only to shorten the processing time of machine tools, but also to minimize the use of auxiliary materials such as loading and unloading. time.
The above-mentioned trial production of the quick lifting mechanism has successfully solved the problem that plagued the loading and unloading station of the high-speed machining center for a long time, and effectively shortened the production cycle of the machine tool. Moreover, parabolic transitions are used at the parts where the speed changes, the acceleration is kept constant, and the impact amplitude is effectively controlled.
The rapid and smooth operation of this structure depends critically on the manufacturing accuracy of the working cam profile of the moving cam. The accuracy of the cam under the current machining conditions is easily guaranteed. In summary, the device is simple in structure, convenient to manufacture, stable in operation, and reliable and durable.
Fast lifting mechanism of pallet exchange device in machining center
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