ZERO BACKLASH IN PLANETARY GEARBOX APPLICATIONS – FACT OR FICTION?
Manufacturers in the UK are switching to automation to boost productivity and speed to market so that they can remain competitive; however, backlash within high precision production machinery can add lost motion to the system, decreasing positional accuracy and affecting performance. Eugene Detke, technical manager at APEX Dynamics UK, examines the implications of backlash and how to reduce its impact to near-zero.
Reducing backlash to a perfect zero has been the holy grail for precision gearbox manufacturers and, whilst some companies may claim this level of perfection, it is in actual fact an impossible goal. When gears fit together, backlash is an inevitable result. However, it is possible to supply precision-built gearboxes that can keep operating to maximum effect by ensuring extremely close-tolerance alignment of components in a motion control system. Building an ultra-precise gearbox to obtain
near-zero backlash requires taking measures to avoid defects such as incorrect tolerances, bearing misalignment and manufacturing inconsistencies which all tend to increase the risk of more backlash. This involves investing heavily in specialised tooling and procedures in order to yield the end result of higher accuracy. To achieve a micro backlash level of less than
one arc minute in the performance series, parts must be measured and classed. The parts that drive accuracy are the pinion, planet and internal gear, and the planet carrier. After sorting, the highest accuracy parts are selected to assemble a micro backlash unit, and all units are tested in a minimum of five spots, the highest measurement used as the rating. If it meets the specification, it is laser etched and shipped; if not, it is laser etched with the next classification level and put into stock. Then the process begins again with new components. The gearbox cannot be disassembled and rebuilt due to the risk of damage. The gearing is post heat-treatment ground
to a final accuracy that produces a less than one arc minute unit, no matter what components are chosen. The challenge within the process is how much to harden the gear tooth, which needs to have high surface hardness combined with a softer core. The surface hardness imparts strength, durability and wear resistance, whilst the softer core facilitates absorption of shock loading. Harden too deep and the whole tooth could become too brittle.
The optimum goal is a gradient of hardness
from the surface in. Since the grinding process is removing material at the surface, there needs to be enough depth of hardness to allow for this, whilst not being too hard. High speed servo technology is one solution
growing in popularity because it is more efficient, adaptable and, as we’ve shown, capable of micro backlash accuracy down to less than one arc minute - as well as special versions being designed for easy cleaning and sterilising in an environment involving food grade materials or pharmaceuticals. Servos running at a high speed (RPM) naturally operate at optimal levels when there’s no torsional wind-up. Gearbox manufacturers can utilise a wide
range of modification techniques to reduce backlash, including decreasing the width between centres, tapering, inserting a plastic filler, splitting and pre-loading dual-path configuration, however there are also downsides, such as increased wear and tear of parts and extended assembly time. Another method is to use gear train preloading, which is expensive but suitable for automation solutions where high precision is critical. In addition, there are safe handling and
packaging practices to exclude post-production damage, while speed reducers are typically produced in small batching, which enables thorough quality testing. Other possible measures include custom machining techniques and enhanced dimensional control prior to and during assembly. APEX Dynamics has set a benchmark for the
automation and motion control industry by offering a five-year warranty plan on its entire product range, as well as a three-week lead time, compared to industry-wide timescales of 15 weeks or more. Ultimately, gearboxes offering near-zero
backlash, combined with quiet operation and minimal vibration, will benefit sectors that uses automation or robotics, or other high precision machine tooling and equipment.
www.apexdynauk.com
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www.aquameter.co.uk quameter.co
A LIFESAVER FOR LONE WORKERS
SBES has launched the SBES LifeSaver SC (Structured Cabling) Lone Worker Alarm System, an independent ‘Patch & Play’ lone worker alarm system that connects via an existing in-house structured cabling system. The versatile system provides an alarm that contacts people automatically in the event of an emergency. The SBES LifeSaver SC supports the complete range
of SBES Alarm Devices, including the SBES LifeSaver Ex/ATEX and standard lone worker alarm units, SBES Emergency Help Points, SBES Disabled Toilet Alarms, Swimming Pool Alarms, Gymnasium Alarms, Sauna/Steam Room Alarms and Under Desk Panic Buttons etc. Alarm notifications can be deployed in multiple
ways: SBES LifeSaver Alarm Display Panels, SMS/Text, email, Beacon sounders, Alarm Receiving Centres, Automated Telephone Calls etc. Utilising a building’s existing Structured Cabling
System provides a number of key advantages, including: • Simple to manage • Enhanced flexibility • Reduced installation time • Ease of future upgrades – room to grow • Less disruption to the business • Reduced risk of downtime • Cost-effective
www.sbes.co.uk
PROCESS & CONTROL | DECEMBER 2019/JANUARY 2020
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