Compact linear technology in test devices for electric motors withstands continuous operation

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• What was needed: drylin SHT linear modules, plastic energy chains
• Requirements: the high number of test cycles per year (around 500,000) calls for a reliable linear system with a long service life. At the same time, all components have to be particularly compact, since the multiplexer has to fit into a 19-inch slot.
• Industry: Automotive industry
• Success for the customer: in a direct comparison with a recirculating ball bearing guide, the drylin SHT linear axis turned out to be the optimal solution for the customer. The material pairings in the linear module made of stainless steel, aluminium and an iglidur high-performance polymer ensure a precise, low-friction, wear-resistant and completely lubrication-free linear process.

Figure 1: View of the entire traversing unit with test plugs. The vertical linear unit with reverse lead screw is not visible.

Problem

The automotive industry is increasingly focussing on electromobility. This has an impact on the entire development and supply chain. For example, the electric motors and batteries as well as other e-components must be 100% tested, with electrical specifications such as overvoltage, current levels and contacting taking centre stage.
Integrating such tests into production lines requires new test systems and ideas for optimally embedding the machines into the production environment.
This is where MCW Systemtechnik GbR, founded in 2017, comes into play. The core competences of MCW include the electrical planning and the mechanical construction of machines and (test) systems as well as the construction of control cabinets.
The company has developed the so-called "multiplexer", a device that automates the electrical connection of test items, such as traction batteries, to various measuring devices (Figure 1). The multiplexer can connect electric motors to three measuring devices and, among other things, carry out low-impedance and resistance measurements, a high-voltage test and a short-circuit test. Twelve tests are completed in less than 60 seconds.
The advantage is obvious: the system speeds up end-of-line testing while reducing wear of the expensive test devices.
A particular challenge in the design, however, was the high speed at which each test item goes through the process. The performance and service life of the linear modules for contacting and decontacting are decisive here. The high number of linear movements results from the short test cycles of the end-of-line test. In one year, a multiplexer makes around 500,000 contacts and decontacts. In addition to the service life, the considerable amount of effort required to connect and disconnect the connectors should not be underestimated.
Finally, the multiplexer must be as compact as possible in the area of application and fit into a 19-inch slot. This limits the overall width and the choice of moving components, in particular.

Solution

When searching for a suitable linear system for contacting and decontacting, the MCW designers came across our modular drive technology system, which, in a direct comparison with a recirculating ball bearing guide, turned out to be the optimal solution for the customer.
A drylin SHT linear module is used for the (relatively long) horizontal movement, in which a stainless-steel lead screw is combined with round shafts made of aluminium and lead screw nuts as well as bearing elements made of an iglidur high-performance polymer (Figure 2). The pairing of materials ensures a linear process that is precise, low-friction, wear-resistant and - very importantly - lubrication-free. To achieve the desired speed, a lead screw with a high helix thread is used.
The very short vertical stroke movement of moving into the connector is also carried out with a drylin SHT linear module, which in this case is equipped with two carriages and a reverse lead screw (Figure 1). The drylin units also prove advantageous due to their compact design and meet the space requirements in the application.
To achieve a short cycle time and make the best possible use of the expensive connected measuring devices, there are two switching units in each multiplexer, of which the lower one is mounted "overhead". While one system is measuring, the other can decontact, and there is no downtime.
The drylin linear modules also stand the test with regard to the high number of cycles. The combined design showed that the drylin SHT modules are ideal for the short test cycles and around 500,000 contacts and decontacts.
Finally, the energy chains on the compact drylin SHT linear modules also come from our product range (Figure 3) and have proven themselves in practice with the equally high technical requirements.

Figure 2: The vertical unit moves horizontally on the drylin SHT module, which makes and breaks contact with the connector of the test item.

Figure 3: The highly wear-resistant test plugs and, at the top edge of the image, the well-filled energy chain on the vertical linear module are clearly visible here.