Slip Ring Semi-automated Test System

Slip Ring Semi-automated Test System

This was a really interesting system to build.  The main challenge was to combine sensitive, low-voltage measurements such as 4-wire resistance ( for continuity testing of the slip rings ) and high-tension tests for insulation strength checks.  So at the centre of the test equipment is a high channel-count high-voltage, low resistance changeover switch to allow both high- and low-level measurements to be performed without having to change connectors or the like.

There is also a fairly hefty controlled-speed electric motor to turn the slip ring so that tests such as continuity variation when rotating can be included.  The block diagram below shows how the system was put together.

The idea of the Test Interface is to allow any slip ring models to be connected to the test system: at one end is a generic connector, at the other is the connector specific to the slip ring.  The connecting cable links the test system measurement channels to each of the slip ring conductors.  Hence to connect to a new model all that is needed is a new cable assembly.

 

Test control uses PreciselySo's Precise Test Manager which includes the database option, so test data is automatically stored onto a central database which can be analysed for quality improvement.  Test reports are written for each model to provide a fast way to print test certificates for each item which can be included in the product delivery.

Reports are generated from the database to provide a certificate that can be shipped in the carton with the product.

A feature we used for this system was a stack-light ( "traffic lights" mounted on top of the rack ).  Because the test procedure involves a bedding-in period - allowing the brushes to conform exactly to the shape of the slip ring - there is fair amount of time where the operator is not required and can work on other tasks.  They can simply monitor it by observing the stack light: green for 'working' and yellow for 'needs attention'.

This system replaced a process of mounting the slip ring onto a machine ( for bedding in ), monitoring it during that period, unmounting it, making measurements using hand-held instruments and writing the results on a piece of paper.  That was observed to take around 35 minutes per unit.

With the PTM-driven semi-automated test system, the operation takes less than 2 minutes of activity and provides larger test coverage; for example measurements when rotating, which aids quality assurance.

As an example of pure cost savings, let's assume a low production rate of 14 per day ( the most a single operator could process in an 8-hour shift, pre-PTM ) - that would translate into operator wage savings of around £36,000 per year.  Alternatively, there is an opportunity to increase test capacity to 17 times the original throughput with a single operator although in this case ( with bed-in time ) more test stations would be required.