October 11, 2022
Industrial manufacturing of high-precision miniaturised positioning systems to customer-specific designs generally require sophisticated production strategies. As filigrain miniature roller tables can be integrated with cage control approaches, they become suitable for highly dynamic applications.
Miniaturisation and system integration are significant trends in many areas of industry. While the compactness of motion systems is an essential basic virtue in medical technology, aerospace engineering, and optical equipment, semiconductor, and electronics production specifications also include a high level of dynamics.
For pick and place, testing, bonding, and microscopy applications the demand for greater dynamics goes hand in hand with increasingly fine precision requirements in the µm range.
Next places image shows a linear guide with integrated cage control: PM has a vertical integration of 95 percent for the mechanical components.
Motion systems and their drive, guidance, and measurement systems are following this trend. While numerous standard products are available for large and medium-sized guide rails and slides,
suppliers’ ranges start to thin out as the level of miniaturisation increases.
At the same time, the sheer variety of applications and their specific requirements mean that custom developments or modifications are often essential.
Among the manufacturers that have been establishing a solid reputation for miniaturised linear guides and positioning tables is the company PM, based at Dedemsvaart in the Netherlands. If you thought that the original company name “Precisie Metaal” suggests a supplier of part-finished products, 56 years after the company was founded, you would be very wrong.
Today, the family-run company is a recognised specialist in high-precision linear guides and positioning systems, and is a global leader in miniaturised product variants.
Around 90 percent of the market can be satisfied with standard products from established manufacturers. At PM they have a strong focus on high-precision and highly dynamic miniature positioning systems, many of which are only available from them in this form.
The bearing units and structural components are really the heart of the guides and positioning systems and are completely milled, turned, ground, bored and hardened by PM. The company produces 95 percent of the mechanical components in-house, including the bearing cages (Figure 1). Ball screws, piezo and linear motor drives, linear encoders, and sensors are obtained from external suppliers.
If the guides are used under critical environmental conditions, ceramic components will also be fitted. They provide exceptionally high wear resistance and rigidity.
The smallest slides in the product range of PM are the MSR slides. It illustrates how small yet powerful the miniature roller tables can be. (Figure 2). The smallest version is the MSR 3-8, it has a length of 8 mm and a stroke of 5 mm, with a width of 5.5 mm and a height of 3.2 mm. Even at this size, a high load-bearing capacity of 191 N can be achieved. This is made possible by a special cage design and a crossed roller arrangement.
Thanks to an enlargement of the contact surfaces and a zero-backlash construction, even this tiny product can do great things. It can reach accelerations of up to 200 m/s2 and speeds of up to 2 m/s.
To avoid fluctuations in the friction force and guarantee exceptionally harmonious linear motion, the micro slides do not have a circulation guide on the rolling elements.
However, a problem with highly dynamic guides with no circulation system is what is known as cage creep or slippage. This effect occurs when the cage is displaced from its original position due to very high accelerations or decelerations, stick/slip effects, insufficient tolerances, or preloading. If this impairs the function, it results in increased friction, a reduction in the stroke, and premature wearing of the linear guides.
The use of anti-cage creep technology is a widespread solution to this issue. It involves holding the cage containing the rolling elements constantly in a defined position relative to the guide rail using a toothing mechanism. This prevents an offset between the filigree components, such as can occur at high accelerations or in vertical installation positions. The dynamic load-bearing capacity is thus retained, even in critical applications. The key factor at PM is that this technology can be implemented even at very tiny sizes (next placed image).
The above article is an edited version of the original article as placed in Microproduction magazine, issue 2022.
