Mobile service lift
Random motor controller failures traced back to their root cause - energy fed back during emergency descent - and fixed in the field with a brake chopper retrofit.
- Mechanical engineering
- Electronics
The problem
The 3rd generation of the mobile lift was struggling with reliability problems: in the latest batch, individual motor controllers failed seemingly at random. That meant downtime for the operators, plus support and warranty costs.
The customer could not reproduce the failure on their own test rig. Any solution therefore had to start with fault finding.
On top of that, the Elmo motor controllers used until then were discontinued (NRND).
Manufacturing costs left no satisfactory margin.
Our approach
Together with the customer we interviewed the lift operators, which narrowed the problem down to the descent phase. In parallel, we analysed the failed motor controllers in our own lab.
One lift was fitted with an oscilloscope and additional sensors, followed by intensive test runs - also so the customer could validate the fix before and after.
The root cause: going down, the motors act as generators. On every rapid stop the current in the DC link spiked, overwhelmed the BMS and shut it down. The recovered energy then had nowhere left to go, the DC link voltage jumped - and that voltage spike damaged the motor controller electronics.
Telling was when it happened: only on the emergency descent, which runs faster than the normal lift speed. Some operators had been using the lift in a way it was not meant for, to save time.
The fix was a brake chopper from our portfolio, adapted to the customer's requirements: a small circuit board that watches the DC link voltage, and a power resistor that safely dissipates the excess energy as heat.
The retrofit could be fitted on site with standard tools - four screws and two wires.
What came out of it
The problems with the lift were identified effectively and fixed promptly, with no impact on the customer's own customers.
That avoided expensive knock-on costs from warranty and service handling.
The company's excellent reputation with its customers was confirmed.
The brake chopper used here is available today as a universal product - the same protection, without every machine needing its own development.
HighStep Systems AG, Switzerland
HighStep Systems develops rail-based climbing protection systems and fall arrest equipment. They invented the first climbing lift - imagine a cross between a Segway and a rack railway - for safe, efficient and ergonomic access to workplaces at height and depth that are otherwise hard to reach.
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