The range of applications for drives and gears stretches over numerous technological fields. The gear, as found in every motor vehicle, represents only a single small but important sub-application. The automation industry as a whole has a constant demand for new individual solutions tailored to solve particular problems. But again and again, it is called upon to find new ways of transmitting movements that a particular component is required to conduct so as to attain a particular result.

Direct drives - gearless units

In a direct drive, there is no mechanical transmission taking place between the drive unit and the output in the form of gearing. In this situation, the motor, as a driving unit, must be capable of supplying the torque for the output at a particular rotational speed. As there is no gearing in a direct drive, the moment of inertia of all the individual rotating masses is smaller than with comparable drive units with intermediate gears.

An perfect example of a direct drive application is the torque motor. This high-pole synchronous motor operates at a relatively low rotational speed but generates a high level of torque.

Servo drives as support structures in medicine

The term servo drive refers to electrical drives that can be dimensioned for a high speed range. A special characteristic of this type of drive is that it enables the selection of a torque characteristic that is configured for a particular task. Servo motors are constructed to allow the selection of suitable operating or work points on the torque’s characteristic curve. It is thanks to these positive characteristics that servo drives are frequently found in packaging machines or in the field of robotics. These are typical fields in which loads often need to be moved with point precision along a given track curve. A further area of application of servo motors is in the field of medical engineering. An exoskeleton is a support structure made for people with physical disabilities. The aim of the exoskeleton, or external skeleton, is to provide fine motor support for certain physical functions. As a sensitive structure, it considerably simplifies the performance of repetitive, everyday movements for a disabled person and is an invaluable aid to the user. This applies in particular to the active exoskeleton, which uses a separate power supply to feed the servo drives.

The strain wave gear principle

This special type of gear has a unique construction that comprises only three essential components: the wave generator, the flex spline and the circular spline. It enables large transmission ratios from high down to low rotational speeds. A further decisive criterion for the Harmonic Drive® strain wave gear is the complete absence of play, as offered by the CPL-2A component set from Harmonic Drive AG.

The Harmonic Drive® strain wave gear is driven by the wave generator, which is mounted centrically and an elliptical outer contour. A special thin ball bearing is positioned on this elliptical contour that can absorb the elastic deformations in the elliptical contour as it rotates. These elastic deformations are transmitted to the flex spline, which has teeth on its outer contour. The outer teeth of the flex spline mesh with the inner teeth of the circular spline - the third essential component. The number of teeth in the circular spline is generally two more than that of the flex spline with the external teeth. Consequently, one full turn of the wave generator results in a turn of the circular spline that is two teeth shorter, and therefore incomplete. However, if the circular spline’s movement is arrested, a full turn of the wave generator results in an incomplete turn of the flex spline, but in the opposite direction.

Component overview of the Harmonic Drive® strain wave gear

  • Wave generator is a driven elliptical element
  • Flex spline is a deformable cylindrical steel bushing
  • Circular spline is a fixed external ring

Drives for use in aerospace

The unique property of the strain wave gear in that it is fully free of play means that such drives are ideal in the aerospace industry, where they are used in spacecraft. One striking example of their application is in the automatic adjustment of solar panels to supply energy, while another can be found in the course correction units and thrust nozzles used in the spacecraft. Similarly, the precise positioning of antennas is enabled by the use of strain wave gears. As the precision of repeat movements is of great importance in the field of aerospace, the complete absence of play is of central importance when it comes to ensuring the operation of these vital functions.

Drives with planetary gears

The term planetary gear, also known as epicyclic gearing, is derived from the fact that the individual cogwheels - which are denoted as the planet set - not only rotate about their own axis but also about a central wheel, the sun wheel set. Planetary gears feature high torque transmission. In addition, high gear ratios can be achieved with only a few cogwheels. Both the input and the output of planetary gears are in the same axis. In the basic configuration of a planetary gear, the cogwheels are mounted on three shafts. The sun is mounted on the first shaft and it is through this that the propulsion from the motor is generally obtained. The second shaft accommodates the planetary carrier that contains the planet set. The third shaft is mounted coaxially to the other shafts and contains a mounting for the hollow wheel with the internal teeth. It is with these inner teeth that the teeth of the planetary wheels mesh. During operation, the shaft with the hollow wheel is often arrested, but this is not necessarily always the case. When the shaft bearing the planetary carrier is arrested, the result is known as stationary transmission.

A very common application of planetary gears is the differential gearbox found in every motor vehicle. When driving round bends, these gears compensate for the difference in speeds between the wheels following the internal radius and those following the external radius. Another familiar application of planetary gears are the hub gears found in some bicycles.

Special drives built to individual customer specification

This sub-area of drive technology, which always requires an individual approach, is found above of all in the field of robotics. As a representative of automation in this sector, the aim is not only to perform directed movements on certain spatial track curves. A further essential aspect is the ability to control the momentary speed of the component. Any emerging accelerations and decelerations as well as the attendant dynamic mass forces must be taken into account in all considerations.

Drive technology as a pillar of automation

The field of drive technology is extremely diverse and demands a high degree of experience and practical relevance due to the often highly ramified problems associated with it. This is why it is often necessary to replace standard systems with individually modified solutions. In such special cases, it is sometimes necessary to use a combination of several components, both in terms of drives and gears. Thanks to their use in special gears, such as those based on the strain wave principle, which are also employed in the aerospace industry, this type of drive enjoys a high degree of currency. As progress in the field of automation continues, drive technology is set to be of enormous relevance in the future and will have a leading effect on the world of technology.