Kenichi Saruwatari

Influence of Wear and Thermal Deformation on Machined PEEK Plastic Bush and Ti Crank Shaft

In biped walking humanoid robot, toughness, durability and lightweight of joint parts are crucial factors due to parts’ constant exposure to high torque and loads. Such ergonomically challenging conditions create the need for joint systems comprising independent elements capable of keeping the component operable for long periods of time. In our work, we focused on wear and thermal deformation in two different grades of both poly-ether-ether-ketone (PEEK) and polyoxymethylene (POM) plastic bushes. The components used for investigation were bushes typically employed in speed reduction devices in joint models for biped walking humanoid robots. In such joint systems, plastic bushes are directly connected to a crankshaft, playing an important role in the robots movement ability. In order to acquire the knowledge of how to build more efficient systems, the influence of the titanium crankshaft roughness on the frictional heat occurring between the shaft and the polymer bush as well as the input axis-output axis backlash require close examination. Based on Rolling Contact Fatigue test, we established the optimal machining conditions for the crank shafts and bushes. Also, superior to other tested polymers as far as glass transition temperature, wear toughness and thermal deformation are concerned, PEEK was found to be the best suiting material for our investigation.

Three-dimensional magnetic microscopy of early stage fatigue in WMZ of low carbon steel plates (JIS-SS400)

Abstract Cyclic stresses around welding joint part affect the strength of mechanical components. In order to understand the fatigue phenomena caused by the cyclic stresses, non-destructive methods that can be related to number of stress cycles are necessary. In the present work, we used a newly developed scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor and observed three-dimensional magnetic fields of the specimen before and after four-point fatigue testing at room temperature in air. Low carbon steel plates (JIS SS400) were used in the experiments. It was found that the intensity of the magnet field in a direction perpendicular to the specimen surface was strongly affected by the fatigue cycles. This result means that we can evaluate the fatigue in welding joint area using quantitative magnetic field measurements. Furthermore, it was discovered that the key factor to evaluate the fatigue is the range between ‘S’ and ‘N’ (‘peak to bottom’ values) of the magnetic fields. The three-dimensional magnetic fields decrease before the dislocation does not accumulate enough to generate a small crack at the early stage of the fatigue.

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.

Changes in Magnetic Fields in Tool Steel (SKS93, JIS) under Single Tensile Load

Fatigue failure of machine components is caused by cyclic load. Non-destructive observation methods that can be related to stress are necessary to study the fatigue phenomena. In the present work, a three-dimensional scanning Hall probe microscope (SHPM) equipped with GaAs film sensors was used to observe the fundamental features of the magnetic fields in a tool steel specimen (SKS93, JIS B 4404: 2006, equivalent to AISI W4 tool steel) during tensile loading. The nature of the magnetic fields during tensile loadings of 430μstrain and 640μstrain was observed using the SHPM. It was found that the magnetic fields decrease due to the tensile loading.

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.

Localization of Partial Magnetization around Artificial Slits in Square Bars of Medium Carbon Low Alloy Steel JIS S45C

Fatigue failure of steel occurs when cracks form and grow in the material’s stress concentration area. In order to understand the relation between stress concentration and crack propagation phenomena, non-destructive evaluation methods that can be related to in-situ measurements around the stress concentration area are necessary. In the present work, we developed a scanning Hall probe microscope (SHPM) equipped in a GaAs film sensor and observed three dimensional magnetic fields at room temperature in air. Medium carbon low alloy steels specimens (JIS, S45C) were used in the experiments. Only the area around the artificial slit had been magnetized and the effect of the magnetization area on the artificial slit was observed.

Magnetic Microscopic Evaluation of Early-Stage Fatigue in WMZ (Weld Metal Zone) of Low Carbon Steel Plates (JIS, SS400)

Cyclic stresses around welding joint-part affect the strength of mechanical components. In order to understand the fatigue phenomena caused by the cyclic stresses, non-destructive methods that can be related to number of stress cycles are necessary. In the present work, we used a newly developed scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor and observed three dimensional magnetic fields of the specimen before and after four point fatigue testing at room temperature in air. Low carbon steel plates (JIS, SS400) were used in the experiments. It was found that the intensity of the magnet field in a direction perpendicular to the specimen surface was strongly affected by the fatigue testing. This result means that we can evaluate the fatigue in welding-joint area using quantitative magnetic field measurements. Furthermore, it was discovered that the key factor to evaluate the fatigue is the range between “S” and “N” (“peak-to-bottom” values) of the magnetic fields.

Asymmetric change in three dimensional magnetic fields of bearing steel (JIS-SUJ2) under spherical Hertzian contact

Flaking failure of bearings is caused by crack growth and stress concentration. The contact conditions between ball, retainer and race affect the durability of the bearings. Non-destructive methods that can be related to contact conditions are necessary to study and understand the phenomena caused by the contact stresses. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was used to observe the asymmetric distribution of three-dimensional magnetic fields in bearing steel plates (JIS-SUJ2) before and after light load contact tests of 19.6N. It was found that only vertical components of the magnetic fields are slightly affected by the spherical Hertzian contact. Furthermore, the change in the three-dimensional magnetic fields is asymmetric to the contact center and magnetization center.

Effect of Off-Center Magnetization Location on Changes in Magnetic Fields under Single Spherical Hertzian Contact

Tribological failure of machine components, such as wear and flaking failure is caused by contact stress concentration. However, observation of stress under contact load is a difficult task. Non-destructive methods that can be related to contact conditions are necessary to study and understand the phenomena caused by the contact stresses. In the present work, a scanning Hall probe microscope (SHPM) equipped with a GaAs film sensor was used to observe the three-dimensional magnetic fields in a long square bar specimen (JIS-SUJ2) before and after contact tests at 196N. It was found that the changes in the three-dimensional magnetic fields caused by spherical Hertzian contact are not affected by the location of the magnetization point on the specimens surface.

Observation of Magnetic Fields in Medium Carbon Low Alloy Steel JIS S45C under Point Contact Loading

In order to understand the phenomena caused by the contact stresses occurring within surface, non-destructive methods that can be related to contact conditions are necessary. The main purpose of this work is to study the relationship between magnetization location and direction, spherical Hertzian contact and changes in the magnetic field asymmetry. In the present work, we used a newly developed GaAs film sensor-equipped scanning Hall probe microscope (SHPM) and observed magnetic fields in tool steel plates before and after contact tests under 196N load, at room temperature in air. Medium carbon low alloy steels specimens (JIS S45C) were used in the experiments. Around the contact test area, changes in ‘S’ and ‘N’ poles generated by magnetization using a square magnet block were investigated.