Technical Blog

Planetary Gearheads within the Medical Industry

Gearheads are used across a wide range of engineering industries with the aim to provide efficient, precise and reliable gear reduction. Since the development of the Thomson Micron TRUE planetary gearhead, interest has focused on the medical industry. So much so that these gearhead now feature in a spectrum of medical appliances such as blood pumps, infusion pumps, dental equipment, lifting equipment, lung machines and kidney dialysis machines. They are also key in the operation of scanners and patient tables.

How do planetary gearheads work?

Planetary gearheads use a gear arrangement in which three planet gears rotate about a central pinion, or sun gear. The planet gears obit with an internal gear which is cut into the inner circumference of the gearhead. The construction of the gearhead is exceptionally rigid which increases the torsional rigidity and stiffness of the gearhead.

Planet gears share the load attached to the output shaft in such an arrangement that gives planetary gearheads a higher load capacity. As it is feasible to have a quantity of gears within a confined space, high ratios can readily be achieved.

Interest in the medical sector grew after the planetary gearheads were optimised by attaching planet gears with a mobile ‘swing’ unit. This enables the planet gears to pivot, adjusting accordingly so they mesh more effectively with both the sun and the ring gears, whilst sharing the load dynamically between them. This resulted in a 25% increase in torque capacity compared to fixed planet configurations, and a reduction in noise levels.

Frictional losses caused by over-tight meshing with the ring gear are also reduced as the ‘swing’ link improves tooth contact by balancing the load, thus enabling a 3-11% increase in efficiency. Torque ripple can also be reduced by as much as 20% making gearboxes suitable for low and medium speeds.

Planetary Gearheads from Heason Technology 

There are 7 Thomson Micron Planetary Gearheads available for applications which require a high torque-to-volume ratio, torsional stiffness and low backlash. These include:

 

  • XTRUE - ideal for duty cycles this gearhead is the smoothest operating gearhead on the market
  • NemaTRUE - an economical solution for all applications
  • AquaTRUE - suitable for harsh environments
  • DuraTRUE - a high precision solution
  • ValueTRUE - a low-cost, high performing solution
  • UltraTRUE - for applications that require high torque capacities, precision and rigidity
  • EverTRUE - a continuous duty version which is lubricated for life

 

In medical scanning equipment, one of the biggest successes of planetary gearheads is with scanners and patient tables. The use of scanners is becoming increasingly important in medical diagnostics and treatment.

Scanners and patient tables require smooth, precise and coordinated movement of a patient relative to imaging emitters and detectors. Of all scanning systems, including Computed Tomography (CT), Magnetic Resonance (MR) and Positron Emission Tomography (PET), it is Cardio Vascular (CV) that has the largest requirement for coordinated, smooth and synchronised movements.

CV scanners can have 6-7 axes of movement, the patient table another 4-5. So for full 360° scans, it is necessary to coordinate all these axes simultaneously. Space is also a limiting factor as all hardware must be enclosed within scanner and table covers.

There is also the necessity for high-efficiency engineering in order to prevent significant heat build-up. Backlash must also be considered. Any gaps or roughness during this change of axis generates backlash which will disturb image quality. The design of a planetary gearhead provides the highest possible torque output, doing so with high efficiency, low noise and minimum backlash. That way servomotor size can be reduced, keeping the overall size of scanning CV and patient tables to a minimum. This has the added benefit of allowing medical staff to be very close to a patient during set-up of a scanning procedure.

What are the four axis of movement for CV patient tables?

  • Height Axis - the up/down movement which is accomplished using a ball screw linear actuator driven by a servomotor via a Thomson Micron planetary gearhead.
  • Tilt Axis - the movement of a table from the horizontal position to either the patient legs-down or head-down position.
  • Lateral Axis - achieved via a rack and pinion gearing system with the rack-gear-pinion mounted directly on a planetary gearhead output-shaft, with the gearhead being driven by a servomotor.
  • Longitudinal Axis - when standing next to a table on which a patient is lying in a horizontal position, this is the left-to-right/right-to-left movement of the table. The drive mechanism here is similar to lateral movement, using rack and pinion, Micron planetary gearhead and a servomotor.

Speak to one of our specialists to find out how these planetary gearheads can be incorporated into your motion application. Call us on +44 (0) 1403 792 300 or email sales@heason.com.

Article published on: 25/08/2016