Small but perfectly formed gear units

A new manufacturing process has been developed for the production of precision gear units measuring just 8mm in diameter and 1mm in depth. Providing reduction ratios of between 500:1 and 1,000:1, they are touted as a stepping stone towards a new generation of miniature devices. The gear units, based around Harmonic Drive's wave generator, flexispline and circular spline technology, are inherently backlash-free and offer a repeatability accuracy of a few seconds of arc. Maximum output torque is10mNm at an output speed of 100rpm. Miniature gearboxes are not new: we have certainly seen our fair share of them over the years in Eureka. However, conventional manufacturing processes have not always demonstrated the accuracy demanded by smaller gear forms, typically offering a module of 60 to 100µm depending on the tooth geometry. This new production method, based on the LIGA process, will take the module down to 34µm. The inherent inaccuracies with conventional processes tend to create large amounts of backlash. The lower module offered by the new process and the operating principle of the flexispline eliminate this, and the Heason Technologies Group sees applications in a number of specialist and non-specialist arenas. These include medical, laser, photonics, metrology, semiconductor manufacture, robotics, microscopy, space hardware and aerospace applications. According to David Wheeler, the company's managing director: "These precision microgears are a key enabling technology for a new generation of miniature devices in a wide range of application areas”. The manufacturing process is similar to that used in the fabrication of semiconductor devices. Abosrbers and photoresists are used to create the basis of the component and, in order to maintain accuracy over a height of several millimetres, a synchrotron X-ray source is used. This gives tolerances better than 1µm. The initial structures are expensive to manufacture so a different, more cost-effective forming process is required to produce them in commercial volumes. This new process is based on the LIGA process with a special forming process, which is described as a 'second galvanoforming' and is the subject of a patent. X-ray lithography is used to produce highly accurate master moulds that can be reproduced using a process such as injection moulding. These plastic structures serve as moulds for the second galvanoforming process – metal is deposited in the moulds creating the final metal structure once the mould is removed. Design Pointers Pointer: The manufacturing process produces miniature gears which are backlash free Pointer: Reduction ratios of between 500:1 and 1,000:1 are available Pointert: A higher-cost master is used to create multiple lower-cost production moulds