There are more and more cases of using vacuum chucks to grab objects in automated lines such as product packaging, object transport, and mechanical assembly. The soft and flexible suction cup can easily realize the handling functions such as holding, uncoupling, and conveying of the workpiece, and ensuring that the object is not damaged. The holding force is maintained by a vacuum system, which may be provided by a vacuum system consisting of an electric motor, a vacuum pump, and various vacuum devices, or may be provided by a secondary vacuum generated by the compressed air through the vacuum generator. The former requires a separate vacuum system, while the latter can utilize the existing air compression system in the general production process. Therefore, it is very convenient and economical to utilize the secondary vacuum method especially in various packaging operations.
The principle of the vacuum generator is that after the compressed air passes through the contracted nozzle, the high-speed airflow ejected from the nozzle entrains the surrounding static fluid and flows forward together, thereby forming a negative pressure in the receiving chamber to induce a secondary vacuum. Such a vacuum system, especially for working conditions that do not require a large flow of vacuum, is even more advantageous. The author has carried out a detailed analysis of the structure and parameter design of the vacuum generator in the article "The vacuum generation mechanism of atmospheric injectors and the design of its main parameters". The vacuum generator can be designed according to the required vacuum degree.
Use a vacuum chuck to grab an object, and you can transfer it at any angle depending on the shape of the object. The following is a dynamic analysis of the force of the vacuum chuck from two special positions, horizontal and vertical.
1 vacuum suction cup mounting orientation
The vacuum chuck is used for mounting orientation when working in two different positions. When the suction cup is horizontally installed, in addition to holding the workpiece load, the influence of the inertial force of the workpiece on the suction force when the suction cup is moved should also be considered. When the suction cup is installed vertically, the suction force of the suction cup is closely related to the friction between the suction cup and the workpiece.
2 Force analysis
The mechanical model of the vacuum suction cup under good working conditions, the parameters are as follows: ΔPu is the vacuum degree; Fv is the vertical load; Aw is the effective area; Fh is the horizontal load; Pd is the surface pressure of the sealing surface; Fr is the friction force; Ad is the sealing Area; Ad is the force of the sealing area; F is the load force; μ is the friction coefficient between the vacuum chuck and the workpiece; Fs is the suction force; Fa is the acceleration force; x, y is the force analysis coordinate of the vacuum chuck.
According to the working principle of the vacuum chuck and the above-mentioned force, it is necessary to meet the requirements of the normal holding object, that is, the condition for normal operation is: Fd=Pd·Ad>0, and Fr=Fd•μ>Fh, vertical when horizontally installed When installing, Fr=Fd•μ>Fv. It is known that the weight of the object to be held is mkg, and the degree of vacuum is ΔPu, and Fs=ΔPu•Aw. Then set the rotation angle φ, the rotation radius r, the gravitational acceleration g, the clamping time t, Fs1 is the static suction, and Fs2 is the dynamic suction.
a. Static load calculation:
Static suction: Fs1=fv=mg; when the safety factor is n, Fs1=nmg
b. Dynamic load calculation:
When the vacuum chuck is in the horizontal position, the force is in equilibrium, ie:
∑Fx=0 Fh-Fr=0 ie Fh=Fr
That is, Fd=Fs2-Fv
Because the friction force Fr is equal to the product of the force of the seal area and the friction coefficient, namely:
And because the vertical load force Fv is equal to the product of the mass of the object and the acceleration, when the vacuum chuck is in the vertical position, the force is in equilibrium.
3 selection of suction cups
The above is the dynamic suction calculation formula required for the vacuum chuck to hold the object. For large suction objects, heavy suction objects, vibration suctions or suctions requiring quick handling, the working environment coefficient and safety factor must be taken into account when applying the formula. In practice, in order to prevent the suction and detachment from falling off, a plurality of suction cups are usually used for suction and hoisting. At this time, it should be noted that the suction cups that work together are properly arranged, so that the suction and urging force points are as close as possible to the center of gravity of the squirt.
The dynamic design of the vacuum chuck makes the suction cup work safer and more reliable. On the basis of static and dynamic analysis and comparison of the force of two typical stations of the suction cup, it provides a more scientific and safe design basis for the design and application of the vacuum chuck.