When The Drive Can’t Keep Up…

Application-specific drive solutions

Standard drives have a firm place in the automation of industrial machines and processes. The range is huge and it seems as if there is an appropriate solution for every task off-the-shelf solution for every task. But what do you do if this concept does not lead to the desired result?

The market offers all types and sizes of electric motors. Ready-to-use motor controllers or programmable controllers (PLC) are available, which are either already equipped with software, or this is available separately - also in great variety. In this way, drive tasks can be accomplished in just a few steps, and this solution is also economically advantageous, especially for individual applications or small series.

However, things were different for a larger Swiss industrial company: The task initially did not seem at all unusual. The task was to periodically move a small metal lever in a large machine. The path was short, a few millimeters, but the movement had to follow a precisely defined target curve within a variable time of a few milliseconds. It turned out that the mass of the lever, in combination with the required accelerations and a relatively large friction, had been underestimated. The automation partner was busy for days adjusting the cascaded PID control without finding a satisfactory, robust solution. The motor controller was then replaced with the next larger and more expensive model, and the controller configuration was started all over again. This was repeated several times until the customer pulled the ripcord. The project then went to Stettbacher Signal Processing AG (SSP). The agreed strategy was now to develop an application-specific controller, hardware and software, for the task. For this purpose, SSP first made calculations about the necessary motor power along the required trajectory. It turned out that the existing motors were already sufficiently dimensioned. Apparently, the controller and/or the controller clock had previously been unsuitable for the task. So, a numerical model of the dynamics of the entire mechanism was designed. Using this model, a digital control strategy was developed and subsequently the required clock rate of the system was determined. A demonstrator was then built using components already available at SSP to verify the new controller in a real process. This was successful straight away, although during commissioning the control parameters were still slightly optimized to eliminate the influence of model inaccuracies.

Picture 2: SSP’s Application-specific Drive Solution.
(Photo: SSP)

In the next phase of the project, suitable electronic hardware was developed that was designed for continuous operation in harsh environments and - with a view to the customer's other wishes - was provided with additional reserves in terms of latency and control clock. At the same time, voltage regulators as well as interfaces for analysis purposes and to the rest of the machine were integrated, so that no further external components are necessary. The whole thing was packed into a metal case half the size of a CD drive, how they used to be.

Of course, the development by SSP came at a price. However, the cost price of the new solution, including housing and cables, is only a fraction of the previous 70-liter cabinet with its complex internals and wiring. In this way, the development will be amortized in less than a year. From then on, the new solution will contribute to the customer's profit.

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