Search

An earthworm moves by a locomotion mechanism called peristaltic crawling. This mechanism requires less space than others and allows for movement across irregular ground and inside a narrow pipe. In this study, we developed a peristaltic crawling robot using several servo motors, and discussed fundamental characteristics of the locomotion patterns. As a result, it was confirmed that the motions of the robot resemble those of the actual earthworm. Furthermore, the experimental results were obtained that there is an appropriate period for the peristaltic crawling motion of the robot, and the velocity tends to decrease with decreasing friction force, etc.

This paper discusses the pitch (angular tilt) of a moving platform, which is the main factor to determine the accuracy of motion in parallel spring movements. As major causes of the pitch the following factors are considered : (1) inaccuracies of construction such as the inequality in free lengths of the two springs and the inequality in separation of the two springs, and (2) the height at which to drive the platform. The theoretical analyses of the effects of these factors on the pitch, and the experiments conducted to verify the validity of the analyses, are presented. It is shown that the pitch due to the driving condition can be eliminated by proper selection of the driving point. It is also shown that the pitch due to the inequality in separation of the two springs can be eliminated by adjusting the length of a moving platform. Description of a variable-length moving platform, which was devised for this purpose, is included.

This paper describes a rectilinear vibration table specifically developed for performing accurate crosstalk calibration of torsional vibration pickups. It is suspended by parallel fiatsprings, and it incorporates a yaw correction device in onder to minimize the parasitic rotation. The correction device is composed of two identical electrodynamic driving units, which are disposed off-centre so as to generate an adjustable torque in addition to the main thrust. Dynamic behaviour of the moving table is analysed, taking into account manufacturing inaccuracies of the suspension. The theoretical analysis indicates that the parasitic rotation can be minimized over a wide frequency range by proper adjustment of the correction device. The validity of the theoretical analysis and effectiveness of the correction device are verified by experiments. Experimental results are presented showing that after the adjustment the parasitic rotation is reduced to less than ±0.05 arcsec over the frequency range 5 Hz to 48 Hz for a constant-acceleration harmonic excitation of ± 0.1 g. It is pointed out that the correction device is also applicable to statically-driven moving tables. Detailed description of the design and construction of the vibration table is given.

This paper describes a vibration generator specifically developed for performing accurate crosstalk measurements of torsional vibration pickups. The vibration generator consists of a rectilinear vibration generator and a torsional vibration generator which functions as a roll correction device. Dynamic behaviour of the vibration generator is analysed, taking into account manufacturing inaccuracies of the elastic suspension of the rectilinear vibration generator. The theoretical analysis indicates that the parasitic rotation (roll) of the rectilinear vibration generator can be minimized by proper adjustments of the roll correction device. The validity of the theoretical analysis and the effectiveness of the roll correction device are verified by experiments. Experimental results are presented showing that after the adjustments the roll is reduced to less than ± 0.015 arcsec over a frequency range 5 Hz to 14 Hz for a constantacceleration harmonic excitation of ±0.1 g. It is pointed out that the correction device is equally effective when the vibration generator is driven statically. Detailed description of the design and construction of the vibration generator is given.

A taut-wire suspension of the seismic rotor of torsional pickups, particularly suitable for the torsional pickups of low natural frequency, is described. Design formulas are briefly outlined for the torsional stiffness, the sag of rotor due to gravity, the shearing stress of wire, and the possible modeforms of the suspension system. The sag of rotor is considered in some deta a comparison of the sags is made with that of the taut-band suspension, and a suggestion is made for the design to minimize the sag.The taut-wire suspension has been applied to an electrodynamic pickup of low natural frequency and 66mm diameter, of which the sag of rotor, the linearity of torsional stiffness, the creep and hysteresis, and the fatigue limit are examined ; it is concluded that the maximum deflection angle of the rotor should be determined mainly from a consideration of the creep and hysteresis characteristics.

A seismic instrument for measuring the hob-to-table cyclic error of large gear hobbing machine is described in which a large and heavy torsional vibration pickup, currently in use for detecting the non-uniformity of rotation of the machine table, is replaced by a pair of small and light rectilinear vibration pickups mounted tangentially on a periphery of the machine table, 180 apart. Two differential-transformer seismic pickups of 1.6 s natural period are connected so as to be additive for the rotational vibration and null each other for the rectilinear vibration of the machine table. The sensitivity for rotational vibration increases in proportion to the table diameter, the minimum measurable angular displacement being 0.0025 sec of arc for the table diameter of 6 m.From theoretical analysis of the motion of the seismic system under working condition, it is shown that the equality of the sensitivities and frequency responses and the parallelism of the sensitive axes of both pickups, and the accuracy of the machine alignment are important factors in determining the measurement error; and these factors are examined in detail. The operating principle of the instrument and the adjustment and calibration of pickups, together with the test results on the bobbing machines of 2 m and 6 m in table diameter, are outlined.