Quick lifting mechanism for pallet exchange device of machining center

Because of its good flexibility, the horizontal machining center is easy to form a flexible automatic machining line, and has become the preferred equipment master for manufacturers. Among them, the machining center with double pallet exchange device is the most widely used. Its double worktable saves time for workpiece clamping and disassembly.
Because the pallet exchange device needs to be lifted before it rotates, the traditional design in the past is to use the oil cylinder without self-locking function to directly jack up the lifting device, which can ensure safety and stability only under slow operation, otherwise it will cause great impact and unreliable.
Therefore, when developing high-speed machining centers, in order to shorten the lifting time of the pallet exchange device, a fast lifting mechanism is designed, which has strong bearing capacity, small impact force and simple structure, and truly realizes fast lifting.
working principle
The quick lifting mechanism of the double supporting plate exchange device of the high-speed machining center drives the moving cam with the oil cylinder as the power, which accurately realizes the fast, stable, impact-free and low noise of the lifting device during the whole lifting operation. The contour curve of the cam is made up of two straight lines, one oblique line and four parabolas. The contour curve of the cam in the acceleration and deceleration section is designed as a parabola, and the parabola acceleration is constant, which minimizes the impact when the lifting mechanism changes speed.
In order to reduce working time, the lifting mechanism should run quickly during the lifting of the supporting plate. In order to reduce the impact force and noise generated by the lifting device at the moment of activation, contact with the supporting plate, and the moment of travel to the end point, the operating speed of these moments must be reduced.
Therefore, the speed of the lifting mechanism cannot be constant during the whole movement process, but changes. At the same time, considering that the higher the change rate (acceleration) is, the greater the impact force is, it is necessary to design a characteristic curve that can not only adapt to the speed change, but also has good performance, so as to realize the fast and stable movement of the lifting mechanism.
This structure takes the moving cam as the main component, and the contour curve of the cam is formed by two straight lines, one diagonal line and four parabolas. The curved surface structure of the moving cam is used to realize continuous lifting from zero speed - acceleration - constant speed - deceleration - constant speed - acceleration - constant speed - deceleration - zero speed. The profile of the cam in the speed change range adopts parabola, and the motion acceleration of the parabola is constant, which greatly reduces the speed change rate, reduces the impact, and makes the motion stable and reliable.
Mechanical structure
The mechanical structure of the quick lifting mechanism is shown in Figure 1. The mechanism is mainly composed of four parts: driving oil cylinder; Moving cam; Support roller; Push rod.
The specific movement process of the lifting mechanism is as follows: the driving cylinder 1 pushes the moving cam 2 forward, the working contour curve of the moving cam pushes the support roller 3 to make vertical movement, and the support roller drives the push rod 4 to make vertical movement through the pin shaft. The figure shows that the moving cam has moved to the end position and the push rod has reached the highest point.
Work process analysis
The pallet exchange device of high-speed machining center must quickly lift the pallet before turning. The weight of the two pallets and the fixture on the pallet is about 4 tons, and the pallet exchange device itself weighs about 1 ton.
The whole lifting process is as follows: the lifting device accelerates to lift the support plate quickly - slowly contacts the support plate and lifts the support plate - accelerates to lift the support plate - approaches the end point and decelerates - enters the load-bearing state. The lifting stroke of the push rod is 50mm, and the required time is 0.8 seconds.
1. Distribution of motion trajectory
The first vertical stroke is 0mm, and the horizontal stroke is 5mm, which is composed of a straight line.
The second section has a vertical stroke of 12.5mm and a horizontal stroke of 48mm, which is composed of two parabolas and is connected with the rising straight line of the next section. The push rod accelerates 5.48m and then decelerates 7.02m. Lift the device close to the bracket and latch it.
The third section has a vertical stroke of 5mm and a horizontal stroke of 80mm, which is composed of a straight line and moves at a slow and uniform speed to complete the slow contact of the pallet exchange device with the pallet (complete the latch) and prepare to lift the pallet.
The fourth section has a vertical stroke of 32.5mm and a horizontal stroke of 112mm, which is composed of two parabolas and is connected with the straight line of the next section. Accelerate to lift the supporting plate 18.288 mm, and then decelerate 14.212 mm to reach the end point.