How To Achieve The Highest Accuracy in Robotics With Gearboxes

Written by Erica Li of HSOAR

 

Difficulties to Overcome for Highest Accuracy

 

• Complex structures and many parts in motion

High accuracy is obtained through complicated reduction mechanisms, even 200 parts involved in! This puts forward the highest entrance for manufacturing and precision machining techniques.

 

• Unsteady and shorter retention

 Some gearboxes have good precision and very low backlash in the beginning. However, the accuracy levels degrade quickly because not all elements are participating in motion.

When excessive torque is applied while the gear is in motion, the teeth may not engage properly, which causes non-eccentric motion. This results in shortened life and a fatigue failure, while teeth wear excessively. In addition, some parts may experience plastic deformation, and some parts buckle which causes early failure of the gear.

Vibration can occur when the driving frequency of the servo system including the gearbox is at or close to the resonant frequency of the system.

As time goes by, visible tooth crack, rim crack, pitting, interface wear, wave generator wear, diaphragm crack, red cross section crack, etc. appear physically.

 Some gearboxes perform tooth profile modification. The purpose is to try to ensure smooth meshing even though there may be small manufacturing errors, and the teeth may deflect under load. It is recognized that under zero or light load the teeth will not be exactly conjugate.

 

•  Lubrication and Viscous friction

 

Traditionally, it is extremely important to properly grease the component. There are two types of lubrication, oil and grease lubrication, You must know clearly when to replace grease, the wear characteristics of the gear are strongly influenced by the condition of grease lubrication. The condition of the grease is affected by the ambient temperature. various temperatures allow different input rotations. You will need to avoid mixing different kinds of grease/also precaution for special environments and pay attention to grease leakage.

Viscous friction occurs due to lubricant action. This type of friction results from the churning and mixing of lubricant-greatly depends on rpm speed.

 At low rotation, this friction may be negligible, once the gearbox starts to turn, viscous friction increases significantly as rpm speeds up. For example, at an input of 200rpm, viscous friction is the largest contributor of overall friction.

 

• Higher cost

 

Some gearboxes manufacturer offer different design or solution such as software to assist to obtain higher precision, such as using special processing machinery, latest machine tools, techniques, or using helical gear, bevel gear, combinations to replace spur gear, this structure cause higher cost on design and material, production.

 Higher precision will be created through rather more expensive machinery, price will be higher,

 

•  Longer delivery time

 

Some gearboxes may have classified accuracy level, for example, standard backlash: P2 level ( 《5-7 arcmin）

Reduced backlash shown as P1 ( 《3-5 arcmin)

Micro backlash, say P0 level ( 《1-3 arcmin)

For gearboxes with micro backlash, manufacturers will generally need to wait for a longer lead time than gearboxes with standard backlash.

 

•  Larger speed ratio using multiple-stage

 

When high precision planetary gearboxes goes to larger ratio, you will need to connect several gear pairs one after another, design usually turns to multi-stage, and more complex.

 Such as ratio between 12~100, higher backlash occur, larger ratio result in chunky body, bigger size and volume which eyes can see, hands can feel.  

 Overall multiplication factor of multi-stage gearboxes is calculated by multiplying the ratio of each gear stage, A three-stage gearbox is obtained by means of increasing the length of the ring gear and adding another planet stage.

 As the number of gear stages increases, the efficiency of the overall gearbox is reduced. 

 

•  High precision did not cover all items

 

High accuracy and zero backlash, means within 《3 arcmin are not commonly covering all series of products of a gearbox manufacturer, some items may have as per customer’s request, most of them may not. 

How to remove above difficulties?

Precision Cycloidal Reducer is the recommended gearbox that provides the outstandingly excellent accuracy and repeatability, through its innovative Full-contact, All-involved simple steel-ball-rolling cycloidal mechanism.