Based on specific customer feedback, Snaptron Inc., of Windsor, CO, decided to tackle the problem of tactile metal dome placement in production situations. Prior to this time, the placement of metal domes to a substrate was performed by hand, which was time consuming and labor intensive. Using either tweezers or a vacuum pen to pick up a dome from a tray, a factory worker placed the dome into a pocket on the substrate.
Feedback acknowledged two concerns: double-doming, where two or more domes nest together and are inadvertently placed into a single pocket and speed. Existing machines were used to place a variety of SMT components, which slowed down the placement of dome contacts. A single dome-placement machine would greatly benefit companies wishing to increase their production efficiency.
Snaptron set a course to design a machine that would place domes in pockets, primarily for membrane applications, but could be used in other applications as well. Calling the new machine the SureShot™, indicating its superior accuracy and repeatability, the company wanted the design to be compact and portable, producing a tabletop design. The final system is able to place domes inverted (feet up) as well as feet down. It also comes equipped with an integral color touch screen interface, which allows part specifications to be entered and stored to facilitate quick transitions between builds. The interface ultimately allows the customization of specific solutions to be programmed in by the user.
Snaptron's concern at the outset was quality at a competitive price. Having worked with Oriental Motor, of Torrance, CA, for in-house equipment needs, it was the first place the company's designers looked for a solution. Oriental Motor has provided linear and complete motion solutions for 24 in-house automated manufacturing and quality control solutions applications — in force/displacement gauges used for measuring the tactile response of a dome. For the SureShot, engineers decided on three EZ Limo Linear Motion Systems per machine.
Several advantages came with the use of Oriental Motor's products. First and foremost, the EZ Limo exceeded servo motor performance with its lightning-short, fast moves. This, combined with its easy-to-use functionality, allowed engineers to replace existing in-house servo-driven dome placement technology at four times the speed and half the cost. A nice exchange, to be sure. According to Troy Diaz, engineering manager on the project, “Access to the EZ Limo's resolver data meant that we were able to operate with no corresponding homing or end-of-travel sensors.” Troy also mentioned that after a year of daily use the EZ Limo continues to operate contamination-free. No screw or rail lubrication has been needed because the factory lubrication is still present.
Another advantage gained by using the Oriental products was Snaptron's engineers found that driver mode and resolver feedback allowed the motion controller to instruct moves beyond the motor's normal capabilities and still execute position-based functions. An example would be that the SureShot speed was doubled simply by overlapping neighboring moves and removing acceleration and deceleration time effects.
Adjustments had to be made in order to integrate this increased performance solution. For instance, the footprint of the SureShot, 32 × 32 inch, was defined by the length of the EZ Limo, which is 29 inch long for a 16 inch stroke. The design team also had to adjust the control circuits to the motor's long settling time. For a motion system that provides superior operation to others available, these were not the issues the team was concerned about.
Final hardware and software decisions
Tactile metal domes are placed as fast as four per sec by the SureShot automated system. Including the time it takes to change substrates between loads, over 10,000 domes are placed per hour. Comparable systems in the industry pick and place parts and therefore offer significantly slower placement rates.
As for software, the design team structured the system so that time penalties due to processor limitations were eliminated. All critical operational functions had to be prioritized and in many cases software was rewritten to minimize potential time delays. Any delay exceeding 10 ms was targeted. Further, through software positional adjustment, the SureShot system is capable of ±0.005 inch accuracy of its 16 × 6 inch placement area. “In-house we rely on and achieve an accuracy of ±0.001 inch,” Troy said.
For ease of use, the machine was designed to interface through a Windows XP-based touch screen located on the front panel of the SureShot. The system runs on a Snaptron custom-developed software component where functions are intentionally limited for simplicity. Program selection and upload, build, idle, access, position tweak and a recently added teach mode are the only available functions.
The software is a Visual Basic spreadsheet-based application, and programming is uploaded from a PC with network access common to the SureShot. Since dome positioning is inherently simple, there are limited necessary fields to define a program, making it quick and easy.
The patent-pending SureShot placement machine also comes complete with an Arrow™ feeder head. Domes are packaged in cartridges and inserted into the head. A rotating mechanism design provides distribution of the domes and assures that only a single dome is placed in the required pocket. Domes are easily placed onto the required location and moved directly to the next location, eliminating the homing necessary for other machines. The final result is a streamlined process and a faster placement rate.