Achieving Ultra-Fast, Precision Motion with Galil Controller and Schneeberger Linear Stage

By Todd Shearer, Application Engineer

Introduction

Motion control applications typically fall into one of two categories: 1) high speed and high throughput with less stringent accuracy requirements, or 2) lower speed with very high accuracy requirements. However, sometimes an application requires both high speed as well as high accuracy, and when such an application arises, it requires all motion components to be of the highest performance. This was the case for a manufacturer in the automotive test equipment industry.

The application was for the redesign of an existing machine used to test automotive sensor components. The test measurements required extremely short and accurate moves to test the quality of the sensor. In addition, high throughput was required due to the large number of test moves to be performed. The resulting stringent specification involved making a .001" move in 1-2 msec that settled within a window of no more than +/-0.0005" and had an overshoot of less than 0.0005". To meet this challenge, Galil’s DMC-40x0 controller was selected in an open competition for this business, along with a Schneeberger linear motor stage and Copley digital amplifier.

Application Description

In this application, the machine is used for testing the sensitivity of a particular automotive sensor. To do so, there are two critical axes on the machine: a rotary motor moving a drum at constant velocity, and a linear motor which moves the sensor in incremental steps towards the rotating drum. Figure 1 shows a drawing of the machine. The step moves of the linear motor (distance “A” in Figure 1) range from a minimum of 0.001" up to 0.511". The goal is for the motor to be moved and settled within a position window in a time of 1-2 msec per 0.001". A 0.001" move should take 1-2 msec, while a 0.01" move should take no more than 10-20 msec. The motor must be settled within a window of no more than +/-0.0005". It is also very important that there is no overshoot of the motor greater than 0.0005" as it would invalidate the test measurement. A PLC in the system will interface with the Galil controller to command the absolute position where the motor is to move. Once settled, the Galil hand-shakes back with the PLC indicating motion is complete and the position at which it’s settled.

Controller Competition

The customer specification of 1-2 msec for a complete 0.001" move was a target for all potential solutions. It was not a given that any combination of controller, amplifier and motor would be able to meet this specification. Consequently, the customer decided to open the competition to three major control manufacturers who were challenged to prove their system best capable of achieving the greatest performance while also offering ease of use, a competitive price and good technical support.

The competition was set up to see which controller/motor combination gave the best performance at various benchmarks. Move and settle times were measured for linear moves of 0.001", 0.002", 0.004", 0.008", 0.016", 0.032", 0.064" and 0.128". Motion was considered complete when the motor was in the position window of +/-0.0005".

Galil Setup and Results

The Galil DMC-4040 controller was selected for this application based on its high servo bandwidth (up to 32 kHz) and ability to take feedback from a sine/cosine encoder and interpolate at a selected resolution. The controller also gave the customer the required number of I/O points along with the stand-alone Ethernet capability they required.

As mentioned, the Galil controller was paired with a high performance Schneeberger linear stage and Copley digital amplifier. The linear stage was solidly mounted to a granite base, and provided extremely fast, linear response to a control input. The digital amplifier was tuned for a very high current loop bandwidth so it could respond quickly to the Galil control input.

Setup and tuning of the system with regards to the Galil controller had two major portions. First, the sine/cosine Heidenhain encoder had to be connected to the interpolation board found within the Galil controller. This sine/cosine interpolation enables the user to select an interpolation resolution from 32-4096x. For this application, an interpolation of 64x was sufficient, giving a positional accuracy of 0.3125 um. Next, the PID filter was tuned for optimum performance. From testing, it was found that a servo update rate of 16 kHz was a sufficiently fast time base for this system, so the TM value was set to 62.5 usec. Also, Galil implemented an additional tuning command to gain slightly more performance out of the system and contribute to the final successful results. Table 1 shows the filter gains and motion parameters used for this system.

With these numbers, the Galil controller met or exceeded the customer requirements at all move distances. In addition, Galil’s controller exceeded the performance of both competitors as shown in the customer supplied results in Table 2

Conclusion

Galil’s DMC-40x0 is a proven high performance motion controller, capable of meeting or exceeding the performance of the most demanding application. In this application, Galil won the business over two major competitors, one a dedicated controller company with a reputation for the highest performance in the industry, the other being the largest name in the PLC/automation industry. After the customer completed their testing, Galil rated #1 in performance and for ease-of-use in programming.