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issue: February 2003 APPLIANCE Magazine

Switches & Switching Devices
Rotary Dial Improves Blower Vac Function

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by David Simpson, Contributing Editor

"The #1 electric blower vac just got better." The Toro Company of Bloomington, MN, U.S. recently made this claim upon releasing its latest blower vac product series.

This rotary dial from DNA Group, Inc. (Raleigh, NC, U.S.) was included in the Toro variable speed Ultra 225 blower and vacuum. Use of the switch improved operator ease of use

"The #1 electric blower vac just got better." The Toro Company of Bloomington, MN, U.S. recently made this claim upon releasing its latest blower vac product series. The improved design followed a full analysis of its existing blowers, in which the company developed three main objectives. One was to convert to a metal impeller for improved balance and reliability; another was to mold a rubber grip into the handle for comfort; and the third was to add a variable speed function with a rotary dial.

Of the three key improvements, the metal impeller and the "comfort grip" were modifications easily done by the company. For the conversion from a slide switch to a rotary dial, it accepted recommendations offered by DNA Group, Inc., of Raleigh, NC, U.S.

The slide mechanism previously used could be somewhat awkward for the end user. When using the unit as a blower, the linear switch was used as an on-off switch. When the unit was turned around to use the vacuum function, the switch was also turned around, becoming reversed to the end user. Converting to a rotary dial eliminates the confusion and allows identical function when used from either direction.

Changing to a rotary switch with both two-speed and variable speed settings was where the expertise of the switch supplier became critical. Eric Vaughn, president of DNA, and Tim Smith of Electroline Sales (an independent representative for DNA) met with Steve Svoboda and John Hurst, Toro senior design engineers, to discuss the OEM's desired results. DNA and its manufacturing partner, Defond Manufacturing (Hong Kong), then prototyped a rotary switch into an existing blower unit and presented the concept to the OEM's marketing department. This presentation convinced the company, and other options were not pursued or considered. The rotary switch with variable speed function came with little additional cost to Toro and required few adjustments. The supplier met the high-volume demands of the appliance company's production line with JIT delivery.

The CYM series rotary switch was an existing DNA switch series. In its original configuration, the switch offers three main functions. First, it serves to switch the main power source for the blower vac. As the switch is rotated into the ON position, it enters the variable-speed function. The switch remains within the variable speed through the middle travel points of the control. Defond's patented "stepped speed" technology produces the variable speed function. The consistency provided by this technology allows the control to more reliably repeat the speed and power curve. The variable-speed function is achieved by the phase-controlling power delivered to the motor. This phase-controlled power is delivered by a triac that is remotely mounted on a heat sink external to the switch, adding a higher level of control reliability. The third switch function is a high-speed bypass to provide a burst of full power to the unit.

Standard features of the CYM include a compact electronic control, an example of Defond's surface-mount assembly and miniaturization capability, as well as welded lead wires to provide a superior electrical connection. This connection reportedly can withstand more handling than traditional poke-in terminal connections, preventing problems associated with wire retention and handling after-wire insertions.

While the existing CYM switch already had some key features designed in to help prevent common assembly problems, other adaptations were made to prevent assembly and usage problems that were foreseen for the blower-vac applications. DNA's electrical engineer, Clinton Piland, manager of Electronics and Controls, made some recommendations, and Defond then implemented a few modifications to best complement the application and overcome some of the initial obstacles faced during the development stages. One suggestion was to have the triac mounted on an aluminum heat sink within the airflow path to keep the triac cooled for better performance and reliability. There were also several iterations of detents tested to determine the best feel for the blower applications and to minimize over-rotation problems for the end users.

Since the rotary switch required a knob, Mr. Piland recommended that Defond mold and assemble the knob to the switch. Toro engineering provided the knob design to Defond as a ProE solid model file. Defond engineering produced the knob to snap firmly to the switch, eliminating the need for any adhesives or fasteners. The materials were chosen for suitable printing capabilities of the knob markings (printed in-house at Defond) and strength and stability of the shaft and switch construction. In addition, a wire harness with a plug was added to the switch for assembly ease.

The OEM conducted in-house testing, including cycle tests, dust tests, and ball-impact tests, and did field testing that simulated actual environments. During the dust tests, dust particles migrated into the housing, causing ineffective switch functioning. DNA suggested a solution to the failed dust test, allowing the production schedule to remain intact. Minor tooling modifications were made to the switch's center spindle and a felt gasket was added to prevent dust penetration.

By using the same principles of the previous CYM switch, DNA was able to reduce the required design time to meet the OEM's scheduled production dates. While the switch's existing function offered an immediate solution for the variable speed "Ultra 225" blower, it was also tooled as an on-off rotary switch to accomplish the same rotary dial concept and design for Toro's two-speed blowers, the Rake & Vac and Super Blower Vac.

It had been 12 years since Toro had manufactured a variable speed blower. The program had been too expensive and eventually cost reduced out of production. DNA offered a cost-effective design allowing Toro to finally re-introduce a variable speed blower vac. This, in turn, satisfied the end users, allowing them to use the blower in confined spaces, such as the garage, without creating a dust storm, or to remove leaves from flower gardens without pummeling the delicate flowers and plants. Both the individual switch as well as the fully assembled unit are UL approved.

Also from the February 2003 issue of APPLIANCE Magazine:
Switches & Switching Devices: Location Isn't Everything


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