NINJA-I (1990-1993), NINJA-II (1994-). It is dangerous to inspect and perform all the operations on the exterior walls of high rise buildings and of the land bridges on high speed thoroughfares. It also requires a great deal of expense in order to install the needed scaffolding. NINJA is a wall climbing robot developed for the purpose of automating this kind of operation. Units No. 1 and 2 of both have a height of nearly 1.8 m , a left/right width of 0.5 meters, a thickness of 0.4 meters, and a main body weight of 45 kg.
All the legs of NINJA-I, as in Fig. 2, are driven by three prismatic joint actuators in parallel mechanisms. They are oriented to the direction of gravity as much as possible at all times, and manifest th e effectiveness of "coupled drive (a drive method which plans on making high output performance as a system by cooperatively utilizing as much as possible all actuators that are installed)". The feet are compliant to the wall surface while being oriented at all times in the same direction as the body by a new parallel movement mechanism which utilizes conduit wires. The NINJA-II expands the reachable area of this foot mechanism by inserting articulated joints.
As for the special gaits for the purpose of walking on walls with four legs, the optimum gait, coined as the "wall gait", was determined. It has a leg arrangement in the configuration indicated in Fig. 3. The robot is also capable of a dynamic walk with a pace gait at the velocity of 7.5 m/min.
A VM (Valve-regulated Multiple) suction pad has been newly developed which consists of many compact suction pads and of valve mechanisms for controlling the operation of each suction pad. It does not produce vacuum leaks, even on wall surfaces which are contoured and have cracks, as indicated in Fig. 4.
Photo. 1 shows the robot walking on the outside wall of a building. Photo. 2 is the VM suction pad.

1. Shigeo Hirose, Akihiko Nagakubo, Ryosei Toyama; Machine that can Walk and Climb on Floors, Walls and Ceilings, Proc. 5th Int. Cof. Advanced Robotics, Pisa, Italy,, , pp.753-758 (1991)
2. Akihiko Nagakubo, Shigeo Hirose; Wall Gait: A Standard Gait for the Quadruped Wall-Climbing Robot, Proc. '93 Int. Conf. on Advanced Robotics,, , pp.547-552 (1993)
3. Akihiko Nagakubo, Shigeo Hirose; Walking and Running of the Quadruped Wall-Climbing Robot, Proc. IEEE Int. Conf. on Robotics and Automation,, , pp.1005-1012 (1994)