Kiyotaka Ikejo

A Prediction Method of Wear on Tooth Surface for Spur Gears

Gear drives are widely used in various mechanical systems. Therefore, the understanding for the failure mode of gear tooth provides the improvement of various machines. The wear on the tooth surface is one of the important failure modes for the gear drives. The tooth wear changes its profile, and frequently increases gear vibration and noise. However, there are many unclear phenomena about the wear on the tooth surface for the gear drive. In this study, we investigated wear of spur gear using a power circulating-type gear testing machine, and measured the change in tooth profile of the test gears. Furthermore, we developed a computer program to predict the amount of the wear on the tooth surface for the spur gears. The method employs two equations. One is based on the wear theory under lubricated condition that was deduced by Soda. The other is derived from the ploughing wear model. Using these equations, the wear depth on the tooth surface is calculated with the contact stress, the sliding velocity, the oil film thickness, etc. The calculated value of the wear agreed with the experimental data.Copyright

Study on the walking support machine indoors by assisting whole legs

There is currently research to support the construction of a walking assist machine, which machine uses a spatial parallel link mechanism for the elderly or rehabilitants. The flat steps of the assist machine move in parallel with the ground and can support the legs of a person including the soles. We developed a prototype and designed to assist people walking at up to fifty percent power. To grasp the walking phase of each leg of the equipped person, pressure sensors were laid under the thenar eminence and the heel of the sole, and the pressure variation at each sensing point was measured. For safety support, we developed a control method of the walking assist machine to fit the motion in phase by phase. Furthermore, in order to support walking indoors, we investigated the assist methods of turning around during walking and walking on a slope or stairs. A flexible link was installed in the mechanism for taking into account the twisting motions of the waist and ankle. To grasp the behavior of turning around during walking of the equipped person, pressure sensors were attached outside of the flexible link in both crural parts of the machine. As a result of the experiment wearing the machine, the equipped person could turn around during walking at will. To confirm the validity of the supporting method, muscle activity of the leg while wearing the walking assist machine evaluated by using the surface electromyography (called as “EMG”), and calculated the ratio of the integrated EMG (called as “IEMG”) with and without the walking assist machine. The initial results show that the activities of the rectus femoris muscle and the tibialis anterior muscle can be held to approximately 60 percent by wearing the walking assist machine. Furthermore, in order to support walking indoors, we investigated the assist methods of walking on a slope or stairs. The machine was equipped with a gyro sensor and an ultrasonic sensor; the angle of the slope and the size of stairs could recognize and the machine could be controled according to the signals from the sensors. As a result of the experiment wearing the machine, the equipped person could walk on a slope or stairs at will. The subject assisted with the machine was able to walk on a slope up to the angle of plus or minus fifteen degrees.Copyright

Friction Loss of Non-Involute Tooth Profile Gears

In the previous study, we have developed two non-involute spur gears that have involute-cycloid composite tooth profile and modified cycloid tooth profile, and proved that these gears have greater bending strength and surface durability than the involute spur gear. In this study, we measured the friction losses of involute-cycloid composite tooth profile gear, modified cycloid tooth profile gear and involute gear using a power circulating-type gear testing machine, by the oil immersion formula, whose method is based on the oil temperature rise due to the power loss in the gear drives. It was found that the involute-cycloid composite tooth profile gear has the least friction loss in the three gears. Furthermore, we calculated the gear friction losses of these gears. The calculated value agreed with the experimental data.Copyright

Power Loss of Spur Gear Drive Lubricated With Traction Oil

This paper describes the effect of traction oil on the power loss of spur gear drive. In this study, we measured the power loss of super gear drive using several traction oils. We separated the power loss into gear friction loss and oil churning loss. Furthermore, we measured the surface temperature on the gear tooth by the dynamic thermocouple method, and observed the lubrication condition between meshing teeth by the electrical resistance method. Then, we investigated the relationships between the power loss of the gear drive lubricated with the traction oil, the surface temperature on the gear tooth, and the lubrication condition.Copyright

Simulation on the vibration characteristics of elliptical gears

Elliptical gear drive is a typical non-circular gear drive, which can be used to transmit a variable-ratio rotation and power simultaneously. To date, elliptical gears are commonly used in automatic machinery, pumps, flow meters and printing presses. However, the vibration characteristics of elliptical gears have not been clarified yet. Due to the non-uniform rotation, the vibration of elliptical gear demonstrates particular characteristics, which should be paid attention to in practical application. This article presents a simulation method on the vibration characteristics of elliptical gears. The torsional vibration simulation model of elliptical gears is established and the simulation programme is developed. The particular gear mesh characteristics of elliptical gears are determined and both the inertial effects of the driving and driven sides of elliptical gears are taken into account in the simulation programme. By means of the simulation programme, two elliptical gear pairs which are a single elliptical gear pair and a double elliptical gear pair and, for comparison, two circular gear pairs which are of the same gear properties as the two elliptical gear pairs respectively are investigated. The torque variations, the rotation speed variations and the circumferential vibration accelerations of elliptical gears are analysed. Furthermore, the critical rotation speeds of tooth separation of elliptical gear drives are obtained and their relations with the load torques are also unveiled. Meanwhile the experiments of the test gears are carried out. The agreement of the simulative results and experimental results proves the validity of the simulation method on the vibration characteristics of elliptical gears proposed in this article.

Diagnosis of gear damage based on coefficient of variation method by analyzing vibration accelerations on one gear tooth

Since minor gear damage may cause serious failures of the entire equipment, early detection of gear damage is one of the important measures to prevent the machine system from malfunction. This paper proposes a method of diagnosing early gear damage by analyzing the vibration accelerations of one gear tooth. Gears manufactured with three different kinds of methods are tested in this study. Their tooth profile error is different from each other. Therefore, the influence of tooth profile error to the damage diagnosis is also discussed in this study. The vibration acceleration on the gear box was acquired as the original signal. In order to eliminate the interference components from the original signal, the time synchronous averaging method is adopted to process the original signal. Thus, the time synchronous averaging signal of driving gear is obtained as the analytical signal. Because the abnormal wave is not obvious in the whole signal, the vibration accelerations of one gear tooth was extracted from the time synchronous averaging signal for studying in detail. For illustrating the representative character of the vibration signal, statistical parameters are calculated from the vibration acceleration of one gear tooth to evaluate the conditions of gear tooth. In addition, the coefficient of variation method is employed to evaluate the contribution ratio of these parameters to gear damage and the weight coefficient of each parameter is obtained. The statistical parameters are synthesized into a unified feature based on the weight coefficient. The results show that the unified feature distance of damaged tooth is distinctive from the normal teeth, and the gear damage can be detected by the present method in this study.

Detection of Damaged Tooth by Support Vector Machines

Gear is one of the most important and commonly used components in machine system. Early detection of gear damage is crucial to prevent the machine system from malfunction. This paper proposes a method for detection of damaged tooth based on support vector machines. Statistical parameters of standard deviation, root mean square value, maximum value and mean value are extracted from the vibration signal as representative features of tooth conditions to be input to the support vector machine classifier. The validity of the presented method is confirmed by the application of detecting early damaged tooth during the cyclic fatigue test. The vibration acceleration on gear box is acquired as original data. Furthermore, the signal of each gear tooth is separately extracted from the signal for a further analysis.The experimental results demonstrate the effectiveness of the proposed method.

Development of a diagnosis method of a gear tooth surface by predicting laser beam reflection

We developed a new diagnostic method by using a laser beam. This method is as follows: A tooth surface is irradiated by the zonal laser beam from an oblique direction, and then the irradiated laser beam line is shifted along the surface of the tooth according to gear rotation. If the damage on the irradiated tooth surface exists, the voltage proportional to laser reflection increases. We developed the method to predict and make the reflection benchmark on the normal condition according to the gear surface. To make the benchmark of the diagnosis, the three dimensional basic-data map (x: irradiated angle, y: irradiated distance, z: reflection intensity) was created by measuring the gear only whose material, heat treatment, and roughness were same as the targeted gear. By using the equations of tooth profile and fillet curves calculated from the specifications of the targeted gear, the distance and angle relations between the laser sensor and the tooth surface can be derived. By using the three dimensional basic-data map, the benchmark can be created. The measured reflection data of the non-damage gear agreed well with the benchmark, therefore we can diagnose the various specification gears, if the targeted gear’s material, heat treatment, and roughness are same. Finally, by using the benchmark which was made by our developed method, we proposed a novel diagnosis method. The procedure of the method is as follows:1) The benchmark is made from the targeted gear’s specifications.2) To take into account the fluctuation of the benchmark line influenced by the roughness on the gear surface, normal condition area of the reflected data is defined in the range between −0.05 V and +0.05 V of the benchmark line.3) The normal condition area and measured data is compared, if the measured data is deviated from the normal condition area, there is defined as the abnormal area possible to be damaged.To confirm the validity of this diagnosis method, the measured value of the damage area with caliper directly and calculated value from the method as mentioned above. The errors of the area and the location were within 20 %. Therefore, the effectiveness of the method using the benchmark data can be confirmed.Copyright

Self-Locking of 2S-C Type Planetary Gear Train Composed of External Gears

A planetary gear train is used in a transmission in many fields, because it has a smaller size, a lighter weight, and a larger gear ratio than a conventional gear train. However, a planetary gear train has a lower efficiency than a conventional gear train. Self-locking sometimes occurs, in which case the planetary gear train can not be driven, because of a significant low efficiency. In this study, we theoretically analyzed the efficiency of a 2S-C type planetary gear train composed of external gears, and presented the condition in which the self-locking occurs. Furthermore, we examined the self-locking of 2S-C type planetary gear train composed of external gears using several gear sets with different numbers of teeth by the practical test. As the result, the condition of the self-locking which was analyzed theoretically agreed with experimental result.Copyright

Driving Performance of High Reduction Planetary Gear Drive With Meshing of Arc Tooth Profile Gear and Pin Roller

This paper describes a new type planetary gear drive with the high reduction ratio. The planetary gear drive is mechanically similar to a 2S-C type planetary gear, which has two sun gears and one carrier. The planetary gear drive has two pairs of an arc tooth profile gear and a pin roller, which mesh each other. The planetary gear drive has little backlash, a high efficiency, a long fatigue limit, etc., because the tooth contact holds on concave and convex surfaces. In this study, we measured the vibration acceleration, the transmission error, the gear noise, and the efficiency on the new type planetary gear drive by the running test. We discuss and report the driving performance of the planetary gear drive.Copyright