GEARS & GEARBOXES FEATURE
eight axes on its 2.6m arm. The length of the arm means that any errors that come from the base of the robot are magnified when they reach the end of the arm. Accuracy and repeatability are vital in such military applications, ensuring the threat is safely managed and the robot’s operator is not under any danger. Bomb disposal units are often used on
remotely operated vehicles (ROVs). These ROVs are being used in desert environments, presenting terrain and torque challenges. Harmonic Drive gears were used in NASA’s Mars space rover programme in a similar environment. The terrain on Mars is similar to the challenging desert environment on earth. To navigate this terrain, a reliable steering and drive system was required, meaning that the rovers implemented wheel and steering drive actuators. However, to avoid the vehicle being torque limited, all four wheels were actuated with each actuator being capable of applying half of the rover’s 185kg weight in thrust. As well as this, it is important that the steering actuator is able to maintain its position at a 45° angle, while the drive actuator is operating. The same principles apply to the ROVs used in the military, which must have a similar construction to move across the desert terrain. Military vehicles and weapon stations on ships often use antennas to communicate with each other. Just as with other military applications, it is important that the gearing system provides smooth, repeatable movements with absolute accuracy and zero backlash. Harmonic Drive gears, referred to mechanically as strain wave gears, fulfil this role, as demonstrated by their use on the NASA Mars rover. Harmonic Drive gears differ from conventional planetary gears in that the gear teeth form the outside edge of a flex spline. This leaves the central area to be bored into a hollow shaft, to allow data cables and other services to pass through, while allowing continuous rotation. This prevents cable wrap and is essential for cameras, which rotate through 360°. It’s clear that there are a large number of factors to consider when choosing a gear, or servo actuator, to integrate into military equipment. While there is a high level of military spending, which offers many opportunities for companies looking to produce equipment for this sector, they must consider the high levels of reliability and accuracy that are required in often tough environments.
Harmonic Drive T:01785 245190
harmonicdrive.de
REDESIGNING THE GEAR - A CLOSER LOOK AT NEW WAVEPLUS TECHNOLOGY
Sometimes, you only need one small innovation to make something revolutionary. Sliced bread, for example, simply took a stroke of inspiration for Otto Rohwedder to combine automatic bread wrapping equipment with cutting functionality. Graham Mackrell, managing director of Harmonic Drive UK, explains WavePlus technology, a development in strain wave gearing. The strain wave gear has been the pinnacle
of precision gearing since the technology was first developed in 1957, by renowned inventor and founder of Harmonic Drive, Walton Musser. Consisting of just three crucial components - the wave generator, flexspline and the circular spline - and ensuring zero backlash, as well as a high gear reduction ratio, strain wave gears have long been the standard for critical applications. However, the changing face of industry in recent years has driven increasing demand for highly precise large hollow shaft gears. Here, the bore of the gear can be used for running through power cables or data lines. This is absolutely critical for many complex applications that require digital functionality. For example, surgical robots require a constant power supply to operate. Due to the location of the precision gears in the axis of the robot, it is essential that power lines can pass through easily and safely. Making designs and processes more convenient is a powerful catalyst for innovation. After all, sliced bread was
conceived purely to address the minute irritation of manual slicing. Similarly, the lack of hollow shaft in strain wave gears prompted the development of WavePlus. Traditionally, the wave generator of a
strain wave gear is made up of a specially designed ball bearing. This bearing is necessary for the wave generator to rotate precisely, but due to its shape, it is impossible to include a large hollow shaft in the design. WavePlus addresses this issue by redesigning the strain wave gear to use a specially designed needle bearing. This needle bearing uses cylindrical rollers with very small diameters, capable of providing the same precise motion but with a significantly reduced footprint that allows for a wider central shaft-diameter. Something as straightforward as this adjustment revolutionises the way that high precision gearing is delivered to the aerospace, medical and military sectors. It is a design that has worked well for Harmonic Drive’s recently launched IridiumLine component sets, which have shaft diameters of up to 60 per cent of the gear size. The technology also enhances Harmonic
Drive’s ability to offer bespoke designs for customers. WavePlus technology is an advancement that reinvents the strain wave gear principle, in line with the increasingly technical demands of today’s modern applications. While it is only a small change, for modern engineers this may be the greatest development since sliced bread.
DESIGN SOLUTIONS | FEBRUARY 2017
23
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64
