By: Paul Coughlin
There
has been a lot of discussion over the years as to who created the stepping
motor, or at least the industrial 1.8° motor we know today.
The two
relevant companies involved with the design were Superior Electric, originally
in Bristol Connecticut, and Sigma Instruments, originally in Braintree,
Massachusetts.
Although
Superior Electric seems to have the leading edge as being the first, it appears
that Sigma Instruments may have been the true innovator.
In 1952 the
General Electric Company designed a stepping motor to be used with the Superior
Electric variable transformers and rheostats.
General Electric originally sold the motors to Superior, to attach to
the rheostats, and Superior sold a complete system back to GE.
General
Electric sold the stepping motor design to Superior Electric and in the 1960s
Superior improved the design and introduced the M Series hybrid stepping motors
in 1970. These were marketed under the name
Slo-Syn.
However,
in 1952 Sigma Instruments introduced the Cyclonome Stepping Motor, which is regarded
as the first practical two-wire stepping motor.
Unfortunately it would be years later before integrated circuit
electronics would allow for wide spread application use.
The
Series 9 Cyclonome stepping motors were single phase, uni-directional stepping motors
with step angles of 15° (24 steps/revolution) and 18° (20 steps/revolution). Torque ranges were 1 – 12 oz-in.
Cyclonome 9
Series Stepping Motors
Shortly
after, Sigma released the Series 18 AC Synchronous motor. These were two phase, bi-directional
permanent magnet motors with speeds of 360, 450, 600 and 900 rpm at 120 Vac,
60Hz. Torque ranges were 0.6 – 11 oz-in.

18 Series AC
Synchronous Motors
In 1969
Sigma introduced the 20 Series stepping motor, which had solid broached rotor
segments and is closer to the typical
1.8° (200 steps/revolution) stepping motor we know today.
The 21
Series motor, with laminated rotor segments, was introduced shortly afterward. The laminated rotor segments allowed for
cooler, high speed performance and the 21 Series motor became known as the High
Performance Motor.
In 1984
Sigma took a giant leap in innovation and created the Enhanced Stepping Motor. This was a revolutionary design in that we
placed magnets within the stator teeth, thereby concentrating the flux field,
and providing up to 50% more low speed torque.
This was released as the 802 Series motors.

Sigmax
Technology Enhanced Motors
Along the way Sigma released Bipolar Chopper Drives
with patented features such as Mid-Range Instability Compensation and 4-Phase Chopping
circuitry which combined the best of recirculating and non-recirculating
current regulation.
In 1987
Sigma Instruments was sold to Pacific Scientific, to complement their AC Servo
Motors and Permanent Magnet DC Motors with the Stepping Motors.
Since
then other innovations have taken place for the Sigma Instruments motors, such
as the Powermax, Powerpac and CT Series Stepping Motors, but that’s for another
day.
Kollmorgen
now owns and manufactures both the original Sigma Instruments and Superior
Electric 1.8°. Internally we (I) still
argue as to who released first (eh-hem, Sigma!), but as a team of rivals, we
offer the best in the industry.
One last
note about Sigma Instruments, Inc. which I share with my Superior colleagues –
Sigma invented the Boston Whaler. Ok,
not really, but here’s the connection: Included with the stepping motors being
manufactured in Braintree, MA in 1977, Sigma Instruments manufactured power
supplies, solid state and reed relays, sewing machines, outdoor lighting
controls and capacitor switching devices.
The outdoor lighting controls and capacitor switching devices were part
of a division called Fisher-Pierce.
Dick
Fisher, of Fisher-Pierce, invented the Boston Whaler while at Sigma. The Boston Whaler is a fiberglass flat-bottom
boat, which was widely regarded as being unsinkable. These were used by the Navy Seals in Viet Nam
and more popularly seen with Bud and Sandy in the popular 1960s Flipper films
and TV series.
