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

The automotive industry is increasingly focussing on the topic of electromobility. And this also has an impact on the entire development and supply chain. For example, electric motors and batteries as well as other e-components must be tested 100 per cent, with the electrical specifications such as overvoltage, current levels and contacting taking centre stage.
In order to integrate such tests into production lines, new test systems and ideas for the optimal integration of the machines into the production environment are needed.
This is where MCW Systemtechnik GbR, founded in 2017, comes into play. MCW's core competences include electrical planning and the mechanical design of machines and (test) systems as well as control cabinet construction.
The company has developed the so-called "Multiplexer", a device that automates the electrical connection of test objects such as traction batteries to various measuring devices (Fig. 1). The multiplexer can connect electric motors to three measuring devices and carry out low-ohm and resistance measurements, a high-voltage test and a short-circuit test, among other things. Twelve tests are completed in less than 60 seconds.
The advantage is obvious: the system speeds up end-of-line testing and at the same time reduces wear and tear on the expensive test equipment.
However, a particular challenge in the design was the high speed at which each test specimen passes through the process. The performance and service life of the linear modules for contacting and decontacting are crucial 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, however, the considerable force required to couple and uncouple the connectors should not be underestimated.
Finally, the multiplexer must be as compact as possible in the application area and fit into a 19-inch rack. Above all, this limits the overall width and the choice of moving components.

In their search for a suitable linear system for contacting and decontacting, the MCW designers came across our modular drive technology system, which proved to be the optimum solution for the customer in a direct comparison with a recirculating ball bearing guide.
A drylin® linear module SHT is used for the (relatively long) horizontal movement, in which a threaded spindle made of stainless steel is combined with round shafts made of aluminium and a lead screw nut as well as bearing elements made of an iglidur® high-performance polymer(Fig. 2). The material pairings ensure a precise and low-friction as well as wear-resistant and - very importantly - lubricant-free linear process. To achieve the desired speed, a spindle with a steep thread is used.
The very short vertical stroke movement for insertion into the connector is also carried out with a drylin® SHTlinear module, which in this case is equipped with two slides and a reverse spindle(Fig. 1). The drylin® units also prove to be advantageous due to their compact design and fulfil the tight space requirements in the application.
In order to achieve a short cycle time and maximise the utilisation of the expensive connected measuring devices, there are two switching units in each multiplexer, the lower of which is mounted "overhead". While one system is measuring, the other can decontact, so there are no dead times. The drylin® linear modules also prove themselves
with regard to the high number of cycles. The joint design showed that the drylin® modules SHTare ideally suited for the short test cycles and around 500,000 contacts and decontacts.
Finally, the energy chain on the compact drylin® linear modules also comes SHTfrom our programme(Fig. 3) and has proven itself in practice with the equally high technical requirements.