Servoamps: Generic or Custom?

Sept. 14, 2006
When off-the-shelf servoamps more than meet project needs, custom-designed amps might still be the better choice.

Hanan Hurwitz
Danaher Motion
Wood Dale, Ill.

Edited by Robert Repas

Many engineers see the need for custom-designed servoamplifiers when standard off-the-shelf devices fail to meet project needs. Often missed, though, is that custom servoamps might also make sense when off-the-shelf devices contain more features and abilities than an application requires. By not paying for unused capabilities, a custom solution provides the desired performance while actually lowering costs.

Numerous vendors supply servoamplifiers in a bewildering variety of forms and capabilities. Each company seems to have its own idea of what features are best. The variety of options challenges machine builders to identify the product best suited to an application.

Custom servoamplifiers are designed from the start to meet specific machine requirements. While OEMs typically use custom amplifiers to address form, fit, and function, a growing motive for switching to custom systems is cost. So under what conditions should one consider a custom installation?

The servoamplifier market sees two seemingly conflicting trends. As vendors make more products available off-the-shelf, OEMs increasingly view those products as commodity devices rather than specialized electronic equipment. This commodity-centric viewpoint reinforces the perception that the products also have commoditylike prices that drop as competition rises.

Vendors typically counter competition by adding product features rather than reducing prices. They try to make the product appeal to a wider customer base to increase market size and thus boost sales. Prices have not gone up, but neither have they gone down. Manufacturers using the product end up paying for unused features.

Manufacturers often place their prime focus on product costs with only a secondary focus on features and performance. This differs from the situation a few years ago when engineers focused on the feature set. The expectation now is that all products have the same or similar features. Under that scenario, products with the lowest cost get designed into new and retrofit applications.

Many OEMs emphasize component prices in new machines. They want to boost, or at least retain, market share in an increasingly competitive global economy. Manufacturers invest time and resources reevaluating existing designs to reduce cost. Many times retrofit efforts end up with completely new machines. Even in the world of commodity servoamplifiers, designers now look towards innovative options to minimize machine cost. It is exactly for this reason that custom designs can be attractive and, in some cases, necessary.

For example, semiconductor wafer-handling robots typically have three or four servoaxes. Often the robot mounts on a rail along which it moves back and forth between wafer-loading pods or processing stations. One major design consideration in this application is the cabling between the machine controller and the robot. Traditional designs place servoamplifiers within the same area as the machine controller. Long cables run from the amplifiers to the robot motors.

This setup has several problems. The cables are often heavy duty and expensive. They are subjected to continuous bending and so may need to be reinforced.

In this case the solution is simple — mount the drives at the robot. A custom-designed multiaxis amplifier can place the axis controls in a single package attached to the robot base. Benefits include lower wiring costs, enhanced reliability, integrated functionality, and added value.

Shorter cables reduce stress and enhance reliability. Shared functionality lowers system cost. For example, the multiaxis amplifier needs only one point of communication between it and the machine controller instead of one point per amplifier as in the traditional case.

The intent of servoamp customization is to add value and reduce costs. If a product is already designed to meet custom requirements, why not go a few steps further to integrate other machine functions into the amplifier? Examples include various machine sensors and input/output signals. Quite often the amplifier makes use of this data. But, even if the servoamp does not use the signals, it can measure, digitize, and send the information to the machine controller. With the interface in the servoamp, wiring and computing costs typically are lower than with standalone controllers.

An example might be a pressure sensor in a wafer-handling robot. Why not put the electronics for the sensor on the custom amplifier instead of building or buying a dedicated monitor? By adding the pressure-sensor electronics to a custom servoamp, OEMs save both unit and installation costs.

One advantage of custom servoamps is that the amp is not constrained by particular packaging philosophies. Rather, packaging is designed according to what is needed. Traditional servoamp packaging includes such niceties as an attractive cover, mounting flanges, and connectors designed to meet any number of standards that may or may not be relevant for the application.

Being free of the traditional packaging constraints allows the engineer to literally think outside the box. Does the unit really need that Mil-Spec connector? What about mounting the amplifier on the actual machine? This second question may be of particular interest because mounting the amplifier where it is needed on the machine may lower wiring costs and improve reliability. The product may also fit into the available or allocated machine space, removing the need (and cost) for an enclosure.

Many products fail simply because their design is driven by perceived, rather than actual, customer needs. Many fine servoamplifiers do an excellent job managing the trade-offs required to make a product meet the requirements of many different applications. However, custom units simply provide exactly what the customer needs — no more and no less — to meet the true technical and commercial needs of the application.

Form, fit, and function

Custom servoamplifiers were usually used in areas requiring specific form, fit, and function. Today, limiting costs by removing unwanted or unnecessary features plays a bigger role in determining the choice of amplifier.

Form: The packaging and dimensions Fit: The fit of how the product fits into the overall machine system. A prime example is communications: Does the product have communications capabilities that enable it to merge easily into the system?

Function: What activity the product performs. Some examples are the control structures employed in the product, or the protection and diagnostic functions offered.

Custom amplifier development path

Risk management is the key to successful development of a custom servoamplifier. The following principles can serve as a guide along the custom development path.

Partnership: The vendor and the machine builder are partners. A spirit of cooperation is key at all levels, be it management, engineering, or operations. Program management: The vendor must field skilled and experienced program managers dedicated to the development of the product while remaining sensitive to the needs of the machine builder.

Product specification: Product requirements should never reside permanently in the imagination of one person or another. Requirements must be written in detailed specifications. Ideally, the vendor would write this specification based on input from the machine builder. In this way, the vendor gains a deep understanding of what the machine builder is looking for while the machine builder can see whether the vendor actually understands the needs. The vendor and the machine builder may reiterate the specifications several times to develop a closer understanding. The final specifications are then agreed upon at a formal design review.

Avoid changes: Of course, some change to the specification may be required as the program progresses. However, continual or significant changes will adversely impact the schedule, and perhaps even the final product. Changes made late in the program are far more difficult to integrate into the original design. Late changes typically end up as patches added to the software and hardware. This can severely impact the functionality and reliability of the end product.

Be an active partner: The most successful programs are those where the partners take active roles in program development. A specific role may not involve any actual development work, but certainly involves keeping up to date, on a weekly basis, with development progress.

Factors and trade-offs

The cost benefits of custom amplifiers should always be weighed against the risks and associated costs that a custom-development program entails.

The most obvious factor is need. Need evaluates in terms of form, fit, function, and cost. Machine designers should ask whether an existing, off-the-shelf product can fulfill these needs in a costeffective manner or not. If the answer is yes, then there is no need to pursue a custom solution.

Efforts to develop a custom product are only worthwhile if there is sufficient volume. The word "sufficient" is purposely vague in this context, since it depends greatly on the product itself and on the forecast quantities. Some vendors may require a certain minimum forecast quantity, while others may look at the subject with a view for potential revenue. Both factors are relevant.

Cost is the most sensitive aspect of custom-development programs. In many cases, vendors may ask machine builders to bear some of the costs associated with product development and, thus, also carry some of the risk in the success of the project.

Risks from the vendor viewpoint are associated with developing a product for a particular customer. They typically seek mechanisms to cover that risk. Vendors commonly determine a midrange estimate as part of the process. The burden falls on the machine builder who argues that paying for something that does not yet exist puts money at risk.

One way to reach accord between vendors and builders ties the payment of development costs tightly to development progress. The machine builder typically specifies program milestones along which progress is measured and verified. This mechanism is also favorable to the vendor as it adds another dimension of control to the program and helps the vendor meet program goals.

Any custom-development program has an associated timeline. Once the machine builder concludes a custom design is right in terms of form, fit, function, and cost, then the last key in the decision process determines whether the product can reach its intended market in time. The machine builder must demand, and the vendor must provide, detailed development schedules in order for the machine builder to make informed decisions.

A mistake often made at this point is expecting the schedule to be completely accurate. After all, the schedule is being laid out for a product under development. There is always some measure of risk associated with this process. Designing custom products around existing building blocks reduces the risk to the schedule.

One other risk is that the product functionality may turn out differently than what the customer expected. A strong servoamplifier vendor as partner is key to mitigating this risk for all sides.

Risk is greater when developing new technologies or capabilities. A healthy and honest evaluation of scheduling risks is required to achieve the win-win situation both vendor and machine builder desire.

The top six questions to go custom

Why? Is the product I really need available off the shelf? Consider the need in both technical and financial terms.
How much? Is there sufficient volume to justify the development of a custom product?
When? How long is my design cycle? When is the drive really needed for machine integration?
How? How is the customization program going to be managed?
What? Expend the time and effort to properly and completely define the product. Get the vendor to write the specifications and ensure they understand what you need.
Who? Determine the companies that have the technical capabilities required and the business model to make a custom product.

Benefits of custom servoamplifiers

There are a number of beneficial areas to consider for custom servoamplifiers. Any or all might tip the scale towards the use of a custom or OTS configuration.

Custom servoamps meet exact customer needs without the required overhead for noncustomer-specific products.

Shared system components, such as processor, power supplies, and communication interfaces, reduce costs in multiaxis systems.

Multiaxis solutions save space and wiring while typically boosting reliability.

Custom systems provide tight integration within the mechanical constraints of the machine.

Tight integration between customer and drive firmware efficiently makes use of existing computer resources while retaining control over core processes.

Danaher Motion, (866) 993-2624,

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