Machine Design

Ford has a better idea: Open controls for robotic arms

The automaker sees benefits in standardized platforms for the factory floor.

Robot-arm kinematics on the RWT controller are programmed into controller cards from Delta Tau Data Systems Inc. These board-level controllers carry fast digital signal processors for calculating forward and inverse kinematics between world and joint coordinates, as well as real-time dynamic checking of joint limits (position, velocity, and acceleration) for moves programmed in world coordinates. This helps eliminate wrist snap problems that can crop up when passing near singularities.

RWT's Universal Robot Controller, here next to a Fanuc arm, employs Win NT and PC technology to permit continual upgrading with standard electronics and software. It is designed as a plug-and-play system able to retrofit onto any robot.

The idea of open controllers for robots got a boost recently as Ford Motor Co. made an investment in Robotic Workspace Technologies (RWT) Inc. According to Ford's Technology Venture Fund manager Chris Johnson, the automaker teamed up with Fort Meyers, Fla.-based RWT as a way of reducing operational costs in its factories.

RWT produces controllers that can retrofit onto older articulated robot arms, sometimes boosting performance beyond what the arm was capable of when new. RWT uses controller electronics that are PC-based and off-the-shelf. To this the firm adds software it has written to handle the kinematics for robot arms from Fanuc, Kawasaki, ABB, and others. It also adds a programming language used to devise moves. The language is the same no matter whose arm the controller is paired with.

The resulting open architecture platforms, says RWT, are less expensive than upgrading the proprietary controls for the robots. And they attack a problem: Robot controllers become obsolete every seven years on average, and it is not uncommon for new controllers to feature a new programming language. Existing control programs often cannot be used on the new systems. Robot OEMs eventually stop supporting the older models, and spare circuit boards become hard to find.

There are no such difficulties with an open platform, says RWT. The value is in the software, not the electronics which can be upgraded easily. In fact, "We've had conversations with Kawasaki, ABB, and others and offered to give them the controller for a small licensing fee," says RWT president Walt Weisel. "We want to be in the software business rather than the controls business because we know controls are going to get smaller and smaller."

Open controls based on a PC platform address not only hardware costs, claims Weisel, but also training and other kinds of operating overhead that can be significant for large users of robotic arms. "We've seen plants that have a $2 million inventory of PC cards to handle 700 robots. That is common among automakers," he says. "They've found that the overall cost of a robot arm can be four to five times the initial cost because of factors such as downtime, training, and the need to simulate and verify that the arm can do the job for which it was obtained. If you are a user of robots the size of Ford and you can find a technology that reduces the cost of even a small part of these areas, there are major savings."

RWT controllers, called URCs for Universal Robot Controller, are configured in two parts. An industrial PC serves as an operator interface and host controller for up to 32 axes. A second box contains the power module, which interfaces with the robot and translates control commands into the kinematics to move the arms. In some applications, multiple power modules can operate under a single URC control box. The modules can manipulate separate robots or other factory floor equipment such as conveyors and slides. Networking is built in, as is the ability to run third-party PC software for SPC, ISO 9000, or similar applications.

To this is added a standard robot control language called RobotScript which lets operators enter English-like commands to produce desired move sequences. It employs ActiveX technology and is based on Visual Basic Scripting Edition.

Next, month, RWT plans to debut a related language called ControlScript. It is also based on VB Script but allows writing control programs for nonrobotic devices such as bar-code readers, slides, clamps, CMMs, and so forth.

The main applications for the RWT controllers so far have been in spot welding. "We can reduce the time-per-spot by 0.3 sec," says RWT's Weisel. "That is considered huge. It means an automaker can get an extra two or three car bodies into every shift."

Key to this performance is data handling. "We send six axes-worth of information to and from the servos 2,000 times/sec. That is faster than anyone else," says Weisel. "If you are in continuous path mode and want to jack up the speed, almost all robots today wander off the path. We have been able to draw circles up to 300% faster than the older controllers we replace. This means the robot in many cases is no longer the bottleneck that limits production line throughput."

The ability to make use of the latest control hardware makes such speed possible. For example, a third-generation RWT system scheduled to be released at a trade show next month employs a Turbo PMAC2 board from Delta Tau Data Systems Inc. in Chatsworth, Calif. The Delta Tau board calculates arm and joint positions required to implement move commands. It carries an 80-MHz DSP563XX digital signal processor CPU from Motorola, or faster versions of the processor as an option.

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