Kiyoto Itakura

Surface Profile Observation of PTFE Thrust Bearings under Rolling Contact Fatigue in Water

The life of the PTFE thrust bearing under rolling contact fatigue (RCF) was investigated. The different conditions of axial loads and the rotating speeds under water were applied. The shapes of the bearing race before and after the tests were measured by a two-dimensional shape measurement sensor. The wear loss of PTFE bearing was rarely generated and the shape of the bearing changed slightly in the test. However, it was found that the lifetime of PTFE bearing depended on the temperature generated in the contact surface. In our testing machine condition, the bearing was collapsed over a load of 1600 N.

Measurement of Joint Element Transmission Error in a Humanoid Walking Robot

In the present work, a prototype of a joint element to be used in lightweight and compact joints for tall humanoid robots is investigated. The newly developed element consists of a harmonic drive gearing device, a multi axis mechanism and a resin bush. Bushes produced from two kinds of bush materials: poly-ether-ether-ketone (PEEK) and polyacetal (POM) were tested. Furthermore, two testing machines to evaluate the joints were constructed: for the power input-output transmission error measurement and for the investigation of the influence of walking-load on bush wear.

Wear and transmission error between PEEK bush and 7075 aluminium alloy cam plate components in robot joints

In this work, wear of reinforced poly-ether-ether-ketone (PEEK containing PTFE, graphite and carbon fibres) polymer bushes in friction against 7075 aluminium alloy cam plates is investigated in order to establish the application possibilities in transmission parts in humanoid robot joints. The PEEK bush surface conditions as well as the input axis-output axis transmission error (backlash) require close examination. Sliding wear tests were performed on bushes under 900 kgfcm loaded torque, while the cam plate oscillated. Based on the wear observation, it was found that PEEK wear fragments in the interface between PEEK bush and aluminium alloy cam plate formed a PEEK film.

Relationship between Life, Load and Rotation Speed of UHMWPE Bearing under Dry Rolling Contact Fatigue

The polymer bearings have been widely used in recent years. In this study, ultra-high-molecular-weight-polyethylene (UHMWPE) is investigated. In order to investigate the relation between the lives, loads and rotation speeds, rolling contact fatigue tests were conducted. It was found that rotation speed related to the bearing life and wear loss.

Influence of wear and backlash on machined PEEK polymer bushes and 7075 aluminium alloy cam plates used in robot joints

Due to constant exposure to high torque and loads toughness, compressive durability and light weight of joint parts are crucial factors for biped walking humanoid robot parts. When polymer transmission parts are used for the manufacture of humanoid robot joint, wear becomes an important factor in terms of transmission error (backlash) between the input and output axes, ex. between the motor and the robot’s leg joint. In such joint system, a polymer bushes is directly connected to a cam plate, playing an important role in the robots movement ability. In this work, the influence of wear of reinforced poly-ether-ether-ketone (PEEK) polymer bushes in friction against 7075 aluminium alloy cam plates is investigated in order to establish the application possibilities in transmission parts in humanoid robot’s joint. The PEEK bush surface conditions as well as the input axis-output axis backlash require close examination, so that efficient systems can be built. Sliding wear tests were performed on bushes under 0-50kgfcm loaded torque while the cam plate oscillated. Based on the wear observation, it was found that in a high load range the backlash increased along with number of cycles due to PEEK bush wear. The bush surface roughness also increased during testing. Roughness of PEEK bush surface and the loaded torque for output axis were significantly related to backlash of output axis in robot joint.

Measurement of fatigue and wear of PEEK bush and A7075 cam plate in humanoid robot joints

Abstract Machine elements in humanoid robots for our life support require light weight, high accuracy and high output torque. In order to achieve low transmission error of the humanoid robot joints, wear of reinforced poly-ether-ether-ketone (PEEK) bushes against the 7075 aluminium alloy cam plates is investigated. Sliding fatigue wear tests of PEEK bushes in the humanoid robot leg joint were performed under various load torques. In the case of the bush under 127 Nm load torque at 5·7 mm s−1 sliding velosity, the backlash values were stable after the running process in fatigue wear test. PEEK film was formed by the friction between PEEK bush and 7075 cam plate under compression load. The oscillation angle of the output axis in the robot joint was stable after early stage because of the solid lublication caused by the film. This means the backlash value was stable and decreased due to the PEEK film between the bush and the cam plate.

Change in Backlash of Humanoid Robot Joints under High Load

In this work, wear of reinforced poly-ether-ether-ketone (PEEK) polymer bushes in friction against 7075 aluminium alloy cam plates or titanium crankshafts is investigated in order to establish the application possibilities in transmission parts in humanoid robot joints under high load torque. The PEEK bush wear requires close examination as well as the input axis-output axis transmission error (backlash). Sliding wear tests were performed on bushes under 4000 kgfcm (392 Nm) load torque, while the cam plate oscillated in the humanoid robot leg joint evaluation system. The robot joint using PEEK bush achieved quite small backlash after the fatigue wear test.

Observation of Wear Surface between Pure PEEK and Counterpart Materials; Titanium and 7075 Aluminum Alloy, in Robot Joint

In our recent work, in order to realize joint element in lightweight and compact joints for tall humanoid robots, a new joint element was designed. It consists of a harmonic drive gearing device, a multi axis mechanism and a resin bush. The resin bush slides on a titanium crankshaft of the pole shape while the joint works. However, the bush was stuck, and stopped movement of the joint. In our present work, we observed the bush surfaces against two materials; the titanium and the 7075 aluminum alloy have been used. We could observe the differences between the titanium and the 7075 aluminum alloy by an optical microscope after the fatigue tests.

Measurement of Backlash and Fatigue Wear of PEEK Bush in Robot Joint under Middle Load

In order to establish the application possibilities in transmission parts in humanoid robot joints, wear of reinforced poly-ether-ether-ketone (PEEK) polymer bushes in friction against 7075 aluminium alloy cam plates is investigated. Additionally the transmission error (backlash) in robot joint was measured. The PEEK bush wear requires close examination as well as the input axis-output axis transmission error. Fatigue wear tests were performed on bushes under middle load at 3000 rpm motor speeds, while the cam plate oscillated in the humanoid robot leg joint evaluation system under 1300 kgfcm (132 Nm) load torque. The robot joint using PEEK bush achieved stable small backlash due to good friction perforance.