Membrane keypads are an attractive and low cost alternative to mechanical switches and other panel-mounted components in OEM applications. They offer a virtually unlimited choice of colors, graphics and materials, LED or liquid crystal displays.
At the same time, membrane switch technology is not by itself capable of replacing components that retain their state or settings, depend on analog inputs and outputs, or implement simple control loops.
Monopanel Technologies, Inc. (West Allis, WI) has been a leading manufacturer of custom membrane switch assemblies since 1974. Monopanel Technologies provides front panel assemblies that typically utilize rigid PCB substrates. The ability to provide complex value added assemblies differentiates Monopanel from other membrane switch suppliers and gives OEM customers a real competitive advantage. Their patented, tamper resistant, Endura-SwitchTM design provides a thick graphic overlay for harsh, abusive membrane switch environments.
In October 2000 Monopanel Technologies began working with Wisconsin Oven Corporation (East Troy, WI), a leading OEM supplier of industrial convection and infrared ovens, to provide an updated control panel for their printing plate industrial ovens. The current design utilized electromechanical switches, gauges, counters and timers manually assembled to a metal front panel. To bring the new design concept to reality Wisconsin Oven relied on the engineering resources of Monopanel and Adicon Consulting and Design (Milwaukee, WI). Adicon is a consulting and engineering firm providing electronic product development and software for industrial controls, instrumentation, data acquisition, and communication products since 1986.
"Our partnership with Monopanel and Adicon on this project has proven successful," says Todd A. Schlender, vice president, sales and marketing, Wisconsin Oven. "Our goals for a stylish, cost effective, and functional upgrade to our controls were all met in a timely and professional manner."
In the initial stage of the design, Adicon worked with Monopanel to provide digital, analog, and AC sensing and switching circuitry as part of an integrated front panel solution. Project goals included designing an interface between the membrane switch panel and the oven and combining various I/O functions on one controller board.
Mechanical switches were replaced with momentary membrane switches with status LEDs. Speed potentiometers were removed from the panel and replaced with digital controls and isolated analog outputs to provide accurate control signals for variable-speed AC and DC drives. Four control-relays and related wiring were eliminated in favor of PCB-mounted relays and incorporated into the new assembly without sacrificing dielectric isolation between AC circuits. The new design also provides programmability through the onboard processor, some enhanced control functions, and operator settings saved in non-volatile memory.
In addition to consulting and design services, Adicon supplied programming, component selection, testing, and sourcing for the controller board assembly.
"Typical PCB components usually offer significant cost savings in key areas including power supply, solid state logic, and switching small loads. Combining the talents of two established providers of custom solutions simplified the specification and design process, and produced an almost seamless product with better features than traditional control panels with minimal NRE cost," said Peter Miczek, project manager at Adicon.
In parallel with the above efforts, Monopanel Technologies worked on the membrane switch front panel design. The new membrane switch was designed with second surface graphics and matte surface texture. This included custom embossed graphics on the function keys and embedded chip LEDs for status indicators. Larger LED display modules replaced mechanical speed setting indicators for better visibility. The panel was laid out to make the controls more intuitive, so an operator can easily follow the control logic from one button to another. The new control panel replaced six electromechanical panel-mounted components and eliminated their control wiring and the associated labor cost. Terminal blocks were replaced with connectors and wire harnesses. Therefore, the final assembly of the finished unit has significantly fewer connection points and will prove to be simpler in assembly and more reliable in the field. In addition, the membrane switch was sealed from the front using an adhesive gasket around the perimeter of the overlay. This environmental seal provides improved chemical resistance while allowing easy cleaning of the front graphics.
"Taking this example one step further, the use of an integrated membrane switch solution can provide OEM customers with any combination of inputs and outputs, application specific functions such as interface to AC drives, sensors, and encoders, embedded control loops, and serial communication ports. Custom graphics on the panel overlay improve the appearance and ease of use of the product. Combining state-of-the-art membrane switch and display technology with I/O in one package reduces the number and cost of most components and connections, lowers the test cost of the final assembly, and improves the reliability of the product," said Martin Hedrich, president and chief executive officer of Monopanel Technologies.
In conclusion, teamwork between supplier and customer generated a final product with a more modern "solid state" user interface. The new panel keeps the same form factor and fits within the current oven enclosure. This synergistic approach helped Wisconsin Oven bring their new product to market in a timely fashion by utilizing engineering and design resources from Monopanel Technologies and Adicon Consulting and Design.