Development of a special application for the inspection and control of different types of car bearings produced in small quantities.

An important manufacturer of Bearings for special applications, has submitted to us the inspection of precision bearings intended for machine tools and aeronautical sector, in order to verify if all the balls are present and if they are of correct type, with regard to diameter and material.

The great difficulty of the performed application stems from the need to check bearings that are special and produced in very low quantities (sometimes a few units) and in many varieties; for this reason, it was not conceivable to create a machine requiring hardware retooling.

We had already created, for the same customer and in different factories, diverse quality control applications of bearings. Despite the fact that these were intended for series production in the automotive sector, requiring normal type change, we have accepted the challenge.

Application development for bearing inspection and control

In order to center all the pieces,within the wide range of diameters that the system handles and without any retooling, we have studied a particular configuration, composed of two opposing actuators, mechanically synchronized with each other, each of which has two intertwined parts : the upper shim parts are used for small bearings, the lower shim parts are used for large bearings. As clearly shown in the photo, this conformation means that these adapt to the diameter of the bearing to be centered, always keeping the center, both for large and small bearings.

The peculiarity of the bearing inspection and control system is that bearings can be different from each other, in each station. The movements are numerically controlled and the software can modify the strokes in real time, in accordance with the dimensions of the bearings read from time to time.

Innovations on the bearing inspection and control system

The implemented inspection system is innovative both for the hardware solutions adopted, and for the software, which has been designed to automatically adapt to the various dimensions (internal and external diameters) and position of the bearings: even in case of a small bearing, the software is able to automatically resize the area and obtain a circular ring with more than the needed resolution for subsequent checks. Everything is performed automatically These software features are characteristic of the LinceoONE software, entirely developed by Vision Device.

How the software for inspection and control of bearings works

• Missing sphere detection

First of all, the software determines the internal and external diameters of the bearing, in addition to the position, in order to automatically adapt the inspection area to the annulus of the bearing; everything is performed in real time and for each single bearing; the presence of too large "holes" is then identified, meaning the absence of a sphere.

• Detection of spheres of different diameters

First of all, the software determines the internal and external diameters of the bearing, in addition to the position, in order to automatically adapt the inspection area to the annulus of the bearing; everything is performed in real time and for each single bearing. In the test area, the positions of the windows between the spheres are identified and, at a later stage, the average diameters (of the visible portion). At this point, the differences between all the diameters are calculated and too wide differences between the minimum and maximum are reported: in this way, the reported values are relative and not absolute ones, in order for the configuration to be able to work for any size of the bearings, without changes to the parameters.

The effectiveness of the control is guaranteed by the fact that, mechanically, the spheres cannot be reduced or enlarged, otherwise the bearing could not be assembled. The precision required must be such as to recognize the difference in measurement with respect to spheres of immediately adjacent dimensions in the list of available spheres sizes.

• Detection of spheres of different materials

The inspection system acquires a backlit image in sequence, in order to to carry out the measurements previously described, and an image in reflected light, in order to analyze the reflection on the spheres and determine the type of material on the basis of the different reflectance (as shown by the following image: a sphere is highlighted in comparison with the adjacent one). Considering that the two images are taken by keeping the part still, the spheres’ position is identified by the image against the light (more reliable), while the reflection is analyzed through the second image, in the corresponding positions:

The control can be relative (i.e. it occurs if all the spheres have the same material), possible without any additional information, or absolute (i.e. it occurs even if all the spheres are of the erroneous material), but in this case it is necessary to define the expected material .