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Servo To Go, Inc.
8117 Groton Lane
Indianapolis, IN

Ph: 317 257-1655

Design Motivation

We produced this card . . . .

To Lower the Cost

Conventional eight axis motion control cards are expensive. To accomplish eight axis of motion control, many servo board suppliers require the purchase of a two board set. Some three axis servo boards cost more than $1,400. The majority of this expense is in the on-board processor or dedicated servo integrated circuits used to perform motion control. Since the volume production of these components is very much less relative to the volume production of components in the PC, their cost is more in comparison. Components which are also used in systems other than motion control, have higher volume, so consequently, their cost is lower.

Also for other producers, by using on-board processors, the cost of hardware design and software development is much greater. For a relatively low volume product such as servo boards, this cost is spread across only a limited number of units, thereby significantly adding to the cost of each one. One way servo board manufactures try to get around this problem is by adding more functionality to the card to make it more "general purpose" and therefore able to reach a larger market. But this just adds unintended complexity and cost for functions that might not really be needed for most applications.

To Lower the Complexity

Almost all other servo boards contain a processor (DSP or other), and sometimes more than one. These processors are used to perform the computations necessary to properly control a motor. The conventional thinking was that these on-board processors were necessary because the main CPU in the PC did not have the processing power to perform the calculations in a reasonable amount of time. This was true in the past, but is no longer so. If the trend continues, and it likely will, it will be even less true in the future. 

Another argument for having an on-board processor is that, without it, a real-time operating system would be required on the main CPU. This is also changing.

An extremely fast servo loop update frequency may be necessary for some applications, but for many, an update rate of 1 millisecond is more than sufficient. This makes an on-board processor unnecessary for most applications.

Complexity such as on-board multi-axis trajectory generators sometimes get in the way. This is especially true in many articulated OEM applications such as robotics and machine tool control, where a sophisticated trajectory is calculated by the OEM on the main CPU, and all that is required by the board is to move to various setpoints. Why pay for two trajectory generators?

The approach, simply stated, is: Our board has less of what you don't want.

To Give Users More Control

Typically, the servo loop is calculated using a processor resident on conventional servo cards. This makes the servo control firmware a proprietary component of their systems and therefore it cannot be changed. Users have no control over what control algorithm is used. Controls students can not experiment with the algorithm. 

An input/output only approach such as ours opens the system to other servo algorithms and control experimentation. 

We are interested in hearing your opinions on this approach. Please feel free to drop us a note.

Copyright © 1999-2008  Servo To Go, Inc.  All Rights Reserved    Last updated: July 2011