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