Harmonic Drive is a general term for devices that achieve motion or power transmission through the elastic deformation of an intermediate flexible component. It is named so because the deformation process of the intermediate flexible component is essentially an asymmetrical harmonic.
Based on the working principle and application conditions of industrial robot drives, the analysis suggests that the performance of grease used in industrial robot harmonic drives requires the following:
Good adaptability, suitable for both indoor and outdoor, and can be used universally in northern and southern regions, meeting a temperature range of -40℃ to 120℃;
Excellent wear resistance to reduce wear on the friction parts of the robot;
Suitable friction coefficient to maintain stable lubrication;
Excellent oxidation resistance, with no significant oxidation phenomena even after long-term use (or lifetime lubrication);
Good tribological properties, low temperature rise, and low energy consumption.
Selection of Thickener
Thickener accounts for 5.0% to 20% of the mass fraction of the grease and determines the high-temperature performance, water resistance, and service life of the grease. Its special fibrous network structure plays a role in adsorbing and fixing the base oil in the grease.
The operating temperature of robot harmonic drive grease is between -40℃ to 120℃. Considering the performance of different thickeners comprehensively, 12-hydroxystearic acid lithium soap is selected as the thickener for the proposed development of robot harmonic drive grease.
Selection of Base Oil
The performance of base oil directly determines the performance of the grease, and the lubrication performance, high and low temperature performance, thermal/oxidative stability, etc., of the grease are directly related to the performance of the base oil.
The performance of grease for robot harmonic drives has high requirements in terms of lubrication performance, high and low-temperature performance, thermal/oxidation stability, and long-term use (or lifetime lubrication). Therefore, the base oil also needs to meet these high requirements.
The low-temperature (-40℃) flow pressure of grease for robot harmonic drives is used as the basis for investigating the base oil. Considering the better low-temperature performance of synthetic base oils, the low-temperature performance of base greases prepared with PAO (polyalphaolefin) and/or synthetic esters was investigated. The smaller the flow pressure of the grease at -40℃, the better the low-temperature performance of the grease.
Additionally, synthetic base oils (PAO and trimethylolpropane ester) themselves have good oxidative stability, which is also an important factor in selecting synthetic base oils as the base oil for grease used in robot harmonic drives.
Selection of Additives
Considering the actual usage conditions of grease in robot harmonic drives, it is necessary to add efficient anti-wear extreme pressure agents and anti-rust anti-corrosion agents to the grease to ensure excellent anti-wear extreme pressure performance and anti-rust anti-corrosion performance.
