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Contributed by William M. Erickson, Staff Engineer, Indramat Division, The Rexroth Corporation

As a supplier of servo motors, drives and computer controls, we gain a substantial competitive advantage by being able to guarantee to our customers that the motors and drives we select will achieve the required performance criteria. Our customers are machine builders who use our servo products to perform motion control in a variety of applications, ranging from high-speed spindles to low-speed rotary tables.

Consider the customer who requires a very precise bandwidth (a measure of how well the real-world application follows the control command). We don’t want to supply a motor whose torque and velocity are so strong it will excite resonances in the machine. Given the mechanical load, the mass of the customer’s machine, and other factors, we determine the appropriate motor and drive, along with the exact set of control parameters.

We have to guarantee to the customer that these parameters will deliver the required performance bandwidth. Until recently, we provided that proof by testing the components in our lab. We would take the selected motor and drive from stock, connect them to a large steel wheel having the same mass as the customer’s machine and then run tests for half a day.

An alternative to this time-consuming process would be to run simulation software to test the components. Initially we were not encouraged by the simulation software we had tested… until we learned about VisSim, an interactive Windows-based modelling and simulation software program. We liked its ease of use, so I ran some simulations with VisSim and compared it with our lab results. VisSim’s predictions matched the lab results on enough tests to convince us of the accuracy and reliability of the software.

I began using VisSim on a regular basis to select the correct motor and drive systems for our customers. The simulations modelled the function of our motor and drive with the function of the customer machine, integrating the mechanical load and electrical properties of the components into a system. VisSim provided two critical components used in selecting a motor: motor velocity and motor torque. Equally important, I used VisSim to assure customers that the selected motor and drive would give them the performance they required.

One of our more critical applications was to assure a customer that our frameless motor technology would provide the solution for optimising the machine-motor fit of a new machine. Responding to market demand for smaller machine volume, the customer’s engineers wanted to downsize the motor volume. Frameless motors seemed the perfect answer. Without a pre-defined frame casing, shaft, bearing structure and cooling package, frameless motors can be as much as one-seventh the volume of conventional framed motors, while achieving the same power rating. They are installed as individual components (a rotor, stator and feedback assembly) and become integral parts of the machine.

The customer’s management would not provide final authorisation for the design until they were confident that it would perform as predicted by the engineers. To assure management of the motor’s performance capabilities, I simulated the machine with the frameless motor, drive and computer control using VisSim.

Because I was able to guarantee that the motor configuration would meet customer specifications, the customer’s management approved the design. The project probably wouldn’t have proceeded without VisSim, and I wouldn’t have had the time to extensively test the machine-motor configuration in the lab. But through simulation with VisSim, I completed the testing in a few hours.

By replacing the conventional motors with the frameless motor, the customer built a machine not only with smaller volume, but with several key advantages: the stiffer frameless motor yields improved product quality, and the options for configuring shafting and bearing structures offer more flexibility. In addition, the cooling system is more efficient and the performance is quieter.

VisSim is supplied and supported in the UK and Ireland by Adept Scientific plc, Amor Way, Letchworth, Herts. SG6 1ZA; telephone (01462) 480055, fax (01462) 480213, email vissim@adeptscience.co.uk; or see Adept’s World Wide Web site http://www.adeptscience.co.uk/. Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.

With offices in the UK, USA, Germany and throughout the Nordic region, Adept Scientific is one of the world’s leading suppliers of software and hardware products for research, scientific, engineering and technical applications on desktop computers.