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Minimal-backlash servo gear units

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article image The SEW-Eurodrive 'BSF' series of helical-bevel gear units.
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A NEW generation of minimal-backlash servo gear units will be showcased by drive solutions provider SEW-Eurodrive at National Manufacturing Week in May.

The re-engineered 'PSF' series of planetary gear units and new 'BSF' series of helical-bevel gear units offer superior torque handling for a given model size and are precision-engineered to maximise power transmission efficiency.

The servo gear units are available with multiple output shaft configurations--including a unique 'flange block shaft' arrangement.

According to Darren Klonowski, SEW-Eurodrive applications engineer, the 'flange block shaft' gear units (PSBF and BSBF models) feature a rotating flange that enables the load to be bolted directly to the gearbox, obviating the need for a coupling.

This unique development significantly reduces backlash--a primary criterion for precision servo positioning systems.

Other gear unit output shaft arrangements within the range include solid shaft with/without key (PSF and BSF models) and a hollow shaft arrangement in the angular helical-bevel gear unit range (BSHF model).

"SEW has engineered the new servo gear unit range to meet three different backlash criteria, depending on the application," Klonowski said.

"The standard backlash figures can be 'reduced' for both the BSF and PSF units, and further 'minimised' for the PSF units, where backlash figures of less than 1 arc-minute are achievable."

Another feature of the SEW-Eurodrive servo gear unit range is the high overload capacity achieved by exactly matched components, allowing high torque transfer and the absorption of large axial and radial forces. This means the gearboxes can be accelerated faster--for example, in belt drive systems and rack and pinion applications.

"These are highly dynamic gear units," said Klonowski. "For good servo performance you need to limit the mismatch (or ratio of external inertia) to 10 to one; lower inertia means quicker acceleration and better stability for the control system."

Compact and lightweight, the PSF and BSF servo gear units are each available in a range of sizes and torque ratings that exceed most others of comparable size on the market.

The planetary gear unit with solid shaft (PSF) range is available in nine different models from 25 to 3000Nm output torque; the planetary gear unit with flange block shaft (PSBF) range has six models from 55 to 1750Nm; while the helical-bevel gear unit ranges (BSF, BSBF, BSHF) have six models each from 40 to 1500 Nm. All models exhibit high overload capacity of up to 400 per cent.

SEW-Eurodrive provides two options for the mating of PSF and BSF servo gear units with servo motors. Standard motor mounting with other brands of servo motor is possible using a standard EQH adapter; however the gear units can also be directly mated with SEW-Eurodrive servo motors--such as the CM or CP series--without the need for an adapter, via unique plug-in pinions inside the motor.

Not only does this provide complete positive connections from the motor shaft to the output shaft, but it significantly reduces the length and weight of the gear unit/motor assembly.

The 'PSF' series of planetary gear units and 'BSF' series of helical-bevel gear units will be showcased at SEW-Eurodrive's stand at National Manufacturing Week '05: AIEE pavilion, stand 4401, Melbourne Exhibition and Convention Centre, May 10 to 13, 2005.

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