To evaluate age-related differences in the expression of heat shock protein (HSP) 27 in periodontal ligament (PDL) cells at the protein and mRNA levels, we obtained PDL cells from the incisors of rats weighing approximately 150 g (young group) and 350 g (aged group) and seeded the cells in culture dishes.Over 2 weeks of cultivation, PDL cells were subjected to quantitative reverse transcription polymerase chain reaction (RT-PCR) to measure HSP27 mRNA, and HSP27 protein expression was examined by immunofluorescence.HSP27 mRNA expression in the young group increased slightly over the 2 weeks, while in the aged group it increased significantly over the same time period.The expression ratio of HSP27 mRNA in the aged group was higher than in the young group at 14 days.Furthermore, immunofluorescence signals for HSP27 were stronger in the aged group than in the young group.These data reveal that PDL cells vary their expression of HSP27 with age, and suggest that in view of such changes in HSP27 mRNA expression, the self-defense mechanism is enhanced in aged PDL cells although their overall homeostatic conditions are suppressed.

A new lightweight six-legged robot that uses a simple mechanism and can move and work with high efficiency has been developed. This robot consists of two leg-bases with three legs each, and walks by moving each leg-base alternately. These leg-bases are connected to each other with a 6 degrees of freedom (DOF) mechanism. While designing this robot, the output force, velocity, and workspace of various connection mechanisms were compared, and the results showed that good performance could be achieved with a serial/parallel hybrid mechanism. The serial/parallel hybrid mechanism consists of three 6-DOF serially linked arms positioned with radial symmetry about the center of each leg-base; each leg-base is composed of two active and four passive joints. Walking experiments with this robot confirmed that this mechanism has satisfactory performance not only as a walking robot, but also as an active walking platform. Furthermore, in this robot, the entire leg-drive mechanism acts as a 6-axis force sensor, and individual sensors at the feet are not necessary. The forces and moments can be calculated from the changes in the joint angles. Experiments conducted verified that smooth contact with the ground by the swing-leg and successful switching from swing to support leg can be achieved using this force control and force measurement method.

We advocate the effectiveness of a walking robot to have a structure with a reduced DOF, not based on a model of real animals, to make the robot lightweight and practical, and discuss a technique for reducing the active degrees of freedom (DOF) of a quadruped walking robot as an example for realizing such objectives. If functions required of a quadruped walking robot are properly organized and the required active DOF is examined, 4 active DOF make it possible to select an arbitrary position on uneven terrain and to move in all directions. We describe a mechanism with 4 active DOF and 2 passive DOF as an example of concrete configurations for quadruped walking robots with 4 active DOF. A robot with a reduced active DOF, namely with 3 active DOF and 2 passive DOF, has a capability to reach an arbitrary position at an arbitrary angle on uneven terrain. An actual mechanical model was manufactured as an experimental model, and a walking experiment was conducted. The mechanical model turned out to be about one-4th in weight compared to a conventional biomimetic model of the same size. Based on the walking experiment, it was confirmed that this mechanical model can carry a load up to 4 times its own weight.

In this paper, partial leg exchange gait for twin-frame walking robot is proposed. This twin-frame walking robot doesn’t have the degrees of freedom (DOF) for moving the center of gravity (CG). Thus, it is impossible to increase the stability margin actively. But using this proposal method, CG can move in the leg exchange phase and obtain enough stability margins. Proposal gait motion is verified through experiments using mechanical model ParaWalker-II.

In general a quadruped has 3 degrees of freedom for each leg, for a total of 12 degrees of freedom. Therefore the mechanism for actuating the leg and control system becomes extremely heavy. This paper describes a new design of a quadruped with 4 degrees of freedom. Arrangement of the degrees of freedom and the principle of walking motion are first explained. Then, verification by a mechanical model is described.

A walking robot that has high ground adaptability and the ability to perform various tasks would be extremely desirable in many fields. It can move efficiently in an outdoor environment and on uneven terrain such as stairs, as well as perform tasks. In this paper, for a six-legged uneven terrain walking robot with two body segments, we examine the number of degrees of freedom, movement performance, stability on uneven terrain, and work performance. In addition, we examine the arrangement of the degrees of freedom suitable for practical uneven terrain work by this type of robot. We also propose that a walking robot with an extra leg extension mechanism and a 6-DOF between the body segments is effective. We adopt this design to ParaWalker-II, which we had previously developed, and verify the effectiveness

To introduce the force control for an uneven terrain walking robot such that it effectively sets the suitable contact pressure of its supporting legs and is able to change from support to swing legs smoothly, the force control for ParaWalker-II, serial/parallel hybrid mechanism that is connected between two frames and contacts ground at three points, is proposed. With this method, the entire leg-drive mechanism acts as a 6-axis force sensor; and the force and moment can be calculated from the changes of each joint angle such that sensors at the ends of the leg are not necessary. Furthermore in the paper; force control and position control can be chosen for each direction in order to smoothly walk on uneven terrain. Smooth contact with the ground by the swing-leg and the changing from swing to support leg is verified through experiments using this force control and measurement method