How to determine whether the positioning structure in the inspection tool is correct and reasonable
At the early stage of the design of the automotive inspection tool, the positioning system of the product drawing should be analysed first. The stability of the positioning system not only affects the manufacturing and assembly of the product, but also may affect the unstable measurement results of the parts during the later use of the automotive inspection tool. Six-point positioning principle can be used to analyse and judge whether the positioning structure in the inspection tool is correct, whether the layout is reasonable and whether the constraints are met.
According to the workpiece degrees of freedom are constrained, workpiece positioning can be divided into the following types
1) Complete positioning Complete positioning means that all six degrees of freedom of the workpiece are constrained without repetition, when the workpiece has dimensional or positional accuracy requirements in the X,Y and Z coordinate directions.
2) Incomplete positioning is when the workpiece is constrained by less than six degrees of freedom
3) Under-positioning is the positioning where the degrees of freedom that should be constrained according to the machining requirements are not fully constrained and the constraint points are insufficient. Under-positioning is not permitted.
4) Over-positioning A positioning condition in which the positioning element repeatedly restricts the product in the same direction of the same degree of freedom is called over-positioning. Whether this positioning condition is allowed or not is mainly judged by the consequences it produces. Over-positioning cannot be used when it causes deformation of the product or interference between the product and the positioning element, which clearly affects the placement of the product.
There are two general methods to eliminate or reduce the interference caused by over-positioning.
One is to change the structure of the positioning element, such as reducing the contact length of the working surface of the positioning element or reducing the fit size of the positioning element, increasing the fit clearance, etc.
The second is to control or improve the position accuracy between the workpiece positioning references and between the working surfaces of the positioning elements.