In the field of orthopedic transplantation, like artificial total hip ball and socket joints, tibial, total knee and ankle implants require highly accurate measurements. The surfaces of these implants are higher-order curves composed of non-uniform rational spline curves (NURBS). The editor of the circuit board found that because the transplant components must match the prosthetic parts or even the parts implanted in the human body, they often have irregular shapes and curved shapes. Complex 3D curves increase the difficulty of measuring all planes from one direction, making it difficult for some types of sensors to effectively measure them.
The video measuring system is suitable for measuring prismatic workpieces with intersecting planes. When the planes intersect, edges appear, and the video can easily measure the edges. Orthopedic implant components are usually composed of continuous regular curves (artificial hip joint accessories) or complex contoured surfaces (artificial knee joint accessories), whose shape is exactly like the contours of human organs. These surfaces have few or no planes or intersecting edges.
Although video sensors are good at measuring edges and surface points, it is very laborious and impractical to use a large number of data points to obtain data of even a linear section of a contoured surface. Triggered probes have the same limitations, because the probe needs to be close to each point and return to the position after triggering-although it has certain feasibility, it is also not suitable for measuring large quantities of products.
The best way to determine whether the artificial knee joint bionic curve profile meets the design requirements is to use laser measurement. How does the laser sensor work in the multi-sensor measurement system? The laser sensor projects light onto the surface of the workpiece. The sensor obtains reflected light and scattered light and automatically calculates the distance between the measuring point of the laser and the workpiece in the 3D space. The laser can measure a point, or when the workpiece moves under the laser or the laser scans the workpiece, a series of data points can also be obtained and calculated. Users can customize the sampling interval and sampling rate.
When the laser beam moves through the workpiece, the measurement software can continuously calculate the distance between the laser and the surface of the workpiece. The closed-loop positioning controlled by the Z-axis platform keeps the laser sensor within the capture range. This allows the precise location of data points to be quickly obtained. Laser focusing is faster and more accurate than video autofocus. Because the laser is a non-contact sensor, it avoids potential damage to the workpiece surface and potential contamination of sterile workpieces.
In most cases, it may be difficult for the operator to fix the knee prosthesis to ensure that the laser is directed at all critical surfaces. At this time, installing the prosthesis on the rotary indexing table is a solution, while reducing the manual loading and unloading of workpieces and fixtures, thereby speeding up the measurement speed.
Generally, a probe is used to establish a reference from the knee bending surface, and then the indexing table is rotated to rotate the knee joint prosthesis to present the most ideal surface measured by the laser sensor. Because it is a reference set on the opposite side of the surface to be measured, the measurement system must be equipped with complete 3D measurement software. When the indexer rotates, the software can rotate the coordinate system. In this case, regardless of the position of the rotary indexer, each data point captured by the laser is traceable in the 3D space controlled by the measurement software.
Another method of measuring the complex contours of knee prostheses is to use the Renishaw SP25 contact scanning probe. The PCB factory learned that, similar to the laser, the operator determines the start and end points of the scan. The difference is that when the system moves on the surface of the workpiece and acquires data points, the probe must always contact the surface of the prosthesis. Unlike the trigger probe, the SP25 contact scanning probe is always in contact with the workpiece. Like lasers, data point density and scanning speed can be customized. When the multi-sensor system is equipped with SP25, it must install the matching 3D measurement software to track the data points in the three-dimensional space.
There are other ways to measure the knee prosthesis fixed on the rotary indexing table. The aforementioned linear laser and contact probe scanning can scan the top surface of the prosthesis on the indexing table. Because the linear scan represents a linear cross section of the 3D workpiece, the cross section can be measured by the video sensor as an edge. Rotate the prosthesis 90 degrees, and when the light hits the workpiece from behind, the cross section becomes an obvious "edge". This technique requires a good measuring lens system with a long working distance and is less affected by the knee prosthesis slope.
Because the "section" is larger than the optical window, when the system automatically tracks edges and acquires data points in multiple windows, functions such as the "edge finder" can be applied just right.
The knee prosthesis is mounted on a rotary indexing table, and its entire surface can be measured. Rotate the indexer slowly, only a few angles at a time, you can complete multiple linear scans (or edge search), and generate a data lattice. These data lattices can be imported into 3D fitting software. After the rotation center is obtained, the software will show how the data of the workpiece is consistent with the CAD model of the workpiece.
Some fitting software can even perform geometric size and tolerance analysis of the data lattice while meeting multiple requirements and any deviations between the illustration and the design file. This kind of analysis can not only be used in the acceptance stage of each workpiece, the manufacturing engineer can also improve the accuracy and efficiency of subsequent workpiece production during the production process.
Medical device manufacturers need to record and control the production process at any time. This process also includes the use of testing equipment to control and monitor product quality. The circuit board factory found that the multi-sensor measurement system can quickly and accurately detect the important dimensions of medical equipment, and minimize the number of workpiece loading and unloading. It is the name of the game to ensure that the produced artifacts meet the design specifications. The final result will affect the health of the medical device manufacturer's balance sheet - and ultimately the patient's health.