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AIA: Linear Actuators Cut Programming, Assembly Times

Exselect Engineering (Toronto) manufactures automated soldering equipment. Its products range from lab-scale machines to multistation turnkey systems for Tier 1 automotive suppliers. Recently, the company built a customized, eight-station Pinpointer 86-8 machine to solder a variety of different automotive junction boxes. The machine is flexible and programmable to accommodate future product lines.

Pinpointer machines solder surface mount printed circuit board assemblies by rotating each board to a set position above a bath of flux or solder. The machines then raise the bath to flood the work area on the boards. Both of these steps require precise, repeatable motion control.

Originally, Exselect used stepper motors with ballscrews to create the required motions. But, the company eventually decided to go with Mechatronics Cylinder linear actuators from Dyadic Systems Co. (Kanazawa, Japan) as well as Dyadic's multiaxis CTC-33 controller to save assembly and programming time. In North America, the Dyadic line is marketed by Mirai Inter-Technologies (Richmond Hill, ON).

To raise and lower the baths of solder and flux Exselect installed six Mechatronics SCN6 linear actuators. Each actuator uses a stepper motor and encoder to drive an acme screw, which in turn moves a nonrotating shaft in and out of the actuator housing. Each actuator comes with a separate servo controller that generates the required motion and sends feedback to the user's PLC to indicate a variety of conditions, including motion-complete and alarm.

The actuators lift the baths to "approach" and "submerge" positions before returning the baths back to a rest position. Velocity, acceleration and deceleration control are critical when positioning the baths, because they are brimming with liquid.

Another four SCN6 actuators are used to position the circuit boards at each station. Board orientations are determined via 24-volt DC signals from the main PLC. By coordinating the eight stations, the Pinpointer is able to completely solder a circuit board assembly in less than 15 seconds.

The CTC-33 can communicate with as many as eight actuators in a single network. Actuators can be rotary, rod-type, rodless, or a combination of all three. Communication is handled through prewired connections. Exselect installed the bath position actuators on a six-axis network and the circuit-board rotating actuators on a four-axis network. It then installed a selector so users can pick one network or the other for programming. The CTC-33 is used to modify the position, speed and acceleration data stored in any of the SCN6 controllers. The actuators can be quickly taught by means of a jog wheel, while position, speed and acceleration data are displayed on an LCD screen.

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According to Exselect president Bill Sund, the company reduced its programming time by a week using the CTC-33 in concert with the Mechatronics cylinders, because the alternative would have required creating a complete teaching interface as well as a closed-loop positioning system from scratch.

Being self contained, the linear actuators also take up less space than the combinations of stepper motors, belt drives, ball screws and bearings used on earlier system, and are easier to install-end users just bolt each unit in place.

"The positioning accuracy is excellent. We observed plus or minus Three Sigma performance within 0.0015 inch," Sund says. He notes that the cylinders with controller cost "much less" than buying various steppers, encoders, controllers, couplings, screws and bearings separately. Overall, Sund says, using linear actuators Exselect "reduced the delivery time on [the] project by one-third."

For more on automated PCB manufacture, call 905-738-4077, visit www.exselect.com or eInquiry 4.

For more on linear actuators and motion control, call 905-763-9442, visit http://miraiintertech.com or eInquiry 5.