Linear drive takes on high-end rack and pinion

The BHD II is an extension of Hoerbiger-Origa original BHD range, and incorporates a precision recirculating ball bearing rail that gives it a load bearing capacity of 2 tonnes - ten times that of earlier models.

Modular linear actuators have become a favourite with design engineers and machine builders over the last decade or so, as they are 'fit-and-forget' systems that save considerable design and installation efforts.

They were originally seen as suitable for light and medium duties only, with rack and pinion drives considered the technology of choice for high load and/or long stroke requirements. But the latter systems have to be built up from basic components, so it is time consuming to develop an optimum configuration for each application, claims Hoerbiger-Origa.

Also, their unenclosed format leaves them somewhat exposed to damage and clogging in typical industrial environments; dirt can build up on them making them unsuitable for hygienic applications in pharmaceuticals, foods, and clean rooms.

Another problem associated with rack and pinions is that the drive motor has to be mounted on the moving carriage. This can add inordinately to the mass being moved and lead to issues with flying leads to power the motor.

Finally there are potential safety issues, in that the meshing of rack and pinion form a potential hazard.

Hoerbiger-Origa said it took the decision to develop a heavy-duty BHD after hearing reports that some users were overloading its medium duty units in preference to using a rack and pinion system.

Like its siblings in the BHD range, the BHD II features a compact low profile actuator, housed in a high strength one-piece aluminium extrusion. The low profile is achieved by mounting the belt pulleys with vertical axes rather than horizontal, so that the two runs of the belt loop are side-by-side instead of one above the other.

The extruded housing is strong enough to be used as a structural machine element in many applications absorbing any static loads present, including side and bending forces.

The dynamic load being moved by the actuator is carried entirely by the recirculating ball bearing rail for low friction, high dynamic performance.A stainless steel sliding seal is mounted in the housing to ensure that the belt mechanism is fully protected from ingress of dirt and oil.

Modular mounting options and dovetail slots for adding sensors and other ancillary equipment are also encompassed within the profile of the housing.

The belt is made from a high performance polyurethane reinforced with stainless steel reinforces, being supplied in 20mm, 25mm or 40mm widths depending on the size of the BHD II unit. It requires no maintenance or adjustment throughout its service life which is measured in years for most applications, according to the company.

The BHD II can run at speeds of up to 5m/s, and acceleration capabilities are up to 30m/s/s, which high enough for cycle times on short stroke applications to be reduced. Stroke length is infinitely variable up to 10m.

It is possible to join two BHD IIs together for even greater strokes, but Hoerbiger-Origa warns that in practice a reduction in speed and thrust performance may be experienced.

Options available include an integral gearbox and bi-parting carriages, according to Hoerbiger-Origa.