Harmonic Gear Reducer Transmission Error Analysis and Detection

Harmonic gear reducer is the key component of the electric servo system, its transmission error analysis and testing play a crucial role in the development, production, testing, assembly of gear reducer. According to the thin shell elastics deformation theory, the harmonic transmission principle is analyzed, and the harmonic transmission error sources. The calculation of transmission error is further discussed; the transmission error formula of harmonic gear reducer considering the case of gear backlash and stiffness is given. A harmonic gear reducer transmission error testing system is designed. This system can achieve the detection for the static and dynamic transmission error of harmonic gear reducer, the accuracy of measuring angular is batter than .

An Automated Testing Assembly for Characterizing Stiffness of an Ankle Foot Orthosis

An ankle foot orthosis (AFO) is a device that provides a controlled force to compensate for the muscle deficiencies in the ankle and helps normalize the gait of the patient. Evidence has indicated that there exists an optimal match correlating the patient’s gait related problems and the AFO stiffness. AFO ankle stiffness is measured by the moment around the ankle joint exerted by the AFO per degree of ankle joint rotation. To date, several testing devices and procedures have been developed to assess the stiffness characteristics of AFOs. Most of the devices are manually driven and may not exactly replicate human leg motion. Objective of developing an automated testing assembly is to identify stiffness characteristics of passive AFOs so as to develop an active AFO with shape memory alloy. We have developed an assembly using aluminum T-slotted profiles, single flange linear bearings, and living hinges from 80/20 Inc. Angle measurement was done by mounting Digital Protractor on the shank segment. The whole assembly was mounted on BOSE ElectroForce 3330 test instrument. dSPACE hardware-in-the-loop solution was used for real time data capture of force and angle sensor output. After assessing the characteristics of passive AFO we incorporated SMA wire in the AFO. Similar tests were conducted to evaluate effect of SMA wires on the overall stiffness of an AFO. The results confirm that SMA wires provide stiffness variation such a way that AAFO can be developed to achieve stiffness variation close to normal ankle stiffness.

A Study of Frictional Forces between Orthodontic Brackets and Archwires

The differences in magnitude of static and kinetic frictional forces generated by 0·022 × 0·030-inch stainless steel (Dentaurum®) and polycrystalline ceramic (Transcend®) brackets in combinntion with archwires of different sizes (0·018 inch and 0·019 × 0·025 inch) and materials (stainless steel, nickel-titanium, and beta-titanium) at a constant ligature force were investigated. A friction-testing assembly using the Instron machine was used. In all cases, the static frictional force was greater than the kinetic frictional force. There were no significant differences in the frictional forces generated by stainless steel and polycrystalline ceramic brackets. Beta-titanium archwires produced greater frictinal forces than the other two materials. Increasing the archwire diameter increased the frictional force.