Terumasa Sawato

New Foot System Adaptable to Convex and Concave Surface

Many control methods have been studied on the assumption that the feet of biped robots contact the ground with four points. However, it is difficult for almost all of such biped robots to maintain four-point contact on uneven terrains because they have rigid and flat soles. In order to solve the problem, foot mechanisms should be studied. In 2003, we developed WS-1R (Waseda Shoes - No.1 Refined) which is able to maintain four-point contact. However, it is difficult to deal with the concave or convex ground because of the problems of the contact detection and sideways slip. So, WS-5 (Waseda Shoes - No.5) has been developed. To avoid the slip of the foot, a cam-slider locking system consisting of a solenoid and a cam is constructed and installed at the foot. Also, linear encoders are employed to measure the position of the foot sliders. Through walking experiments on uneven terrains, the effectiveness of WS-5 is confirmed.

Landing Pattern Modification Method with Predictive Attitude and Compliance Control to Deal with Uneven Terrain

Many researchers have been studying on walking control methods for biped robots. However, the effectiveness of these control methods was not verified in outdoor environments such as pedestrian roads and gravel roads. In this paper, a landing pattern modification method adaptable to uneven terrain in a real environment is proposed which is based on a predictive attitude compensation control and a nonlinear compliance control. This method does not require any other sensors except force sensors. Also, a new biped foot system is described which can form larger support polygons on uneven terrain than conventional biped foot systems. Using the modification method and the foot system, WL-16RII (Waseda Leg-No.16 Refined II) achieved a stable walk on bumpy terrain with 20 mm height and 10 degrees inclination. Furthermore, a stable dynamic walk was realized on a paved road, when a human rode it. Through various walking experiments, the effectiveness of the method was confirmed

Static and dynamic disturbance compensation control for a biped walking vehicle

This paper describes a static disturbance compensation control for a biped walking vehicle. To measure forces and moments caused by a passengerpsilas motion, we use a 6-axis force/torque sensor placed under the passengerpsilas seat. When small external force acts on a robot, only a reference ZMP trajectory is changed inside a support polygon. When large external force over a predetermined threshold force acts on a robot, a waist motion is changed. With only the proposed control, however, a robot cannot adapt to rapid disturbance changes. But we have already developed a dynamic disturbance compensation control, so by combining two controls, a human-carrying biped robot, Waseda Leg - No. 16 Refined V (WL-16RV) realized a stable dynamic walk under unknown external disturbances caused by passengerpsilas static and dynamic motion. We confirmed the effectiveness of our proposal through experiments.

Terrain-adaptive control to reduce landing impact force for human-carrying biped robot

Many researchers have studied on walking stability controls for biped robots. Most of them are highly accurate acceleration controls based on the mechanics model of the robot. However, the control algorithms are difficult to be used for human-carrying biped robots due to modeling errors. In the previous report, we proposed the landing pattern modification method, but it had a problem that a foot landing impact increased when a walking cycle was short. So, we propose a new terrain-adaptive control reducing a landing-impact force. To increase a concave terrain adaptation, we set a target landing position beneath a reference level. To reduce the landing-impact force, we change the position gain control value to a small value at a swing phase. Moreover, we set landing-foot speed at zero when the foot landing is detected by the force sensor mounted on a foot. To follow uneven terrain, a virtual spring is applied along the vertical direction after detecting a foot-landing on a ground, and a virtual compliance control is applied to the roll and pitch axes. In a stable walk while carrying a 65 kg human on uneven terrain, the new control method decreased the landing-impact force than the previous terrain-adaptive control.

Unknown disturbance compensation control for a biped walking vehicle

This paper describes how to compensate unknown external forces caused by a riders motion of a biped walking vehicle. When external forces act on a robots waist, the waist is accelerated so that a measured ZMP may be equal to a reference ZMP. To inhibit the divergence of the waist motion, the reference ZMP is varied inside a support polygon. However, if a large external force acts on a robot, the waist trajectory does not converge by only controlling a reference ZMP. So, ZMP trajectory is varied by changing a foot-landing point. Using the proposed control method, WL-16RIV (Waseda Leg-No. 16 Refined IV) achieved a stable human-carrying walking under unknown external forces which exert forward and sideways on the robots waist. Through various walking experiments, the effectiveness of the proposed method was confirmed.

Development of a Biped Locomotor with the Double Stage Linear Actuator

Previously, the realization of ascending and descending stairs and landing pattern modification control by WL-16RII were reported. However, it is difficult to use the landing pattern modification control when ascending stairs, because of the insufficient stroke of linear actuators. In this report, the design of a double stage linear actuator with a larger expansion and contraction ratio is described. The new linear actuators developed have been installed in WL-16RII, and several experiments were conducted. Through experiments involving walking with a wide step length and ascending a stair with landing pattern modification control, the effectiveness of the actuator developed is confirmed.

Avoidance behavior from external forces for biped vehicle

This paper describes an avoidance behavior from unknown external forces for a biped walking vehicle. To distinguish between external forces from passenger and those from environments, we use the data of a force sensor mounted on foot, and external forces are estimated from ZMP errors. To guarantee a walking stability, the waist position is adjusted to match the measured ZMP to the reference ZMP, and the position of landing foot is adjusted so that the waist trajectory does not diverge. By implementing the developed method on the human-carrying biped robot, the robot realized a stable walk under unknown external forces from environments. When pushing the robot stepping, the robot moved backward and moved away from the generation source of external forces about 400 mm. When pushing the robot walking forward, the robot stopped going forward and prevented from coming closer to the generation source of external forces. We confirmed the effectiveness of the proposed control through these experiments.

Walking Pattern Generation of a Biped Walking Vehicle Using a Dynamic Human Model

This paper describes a passive dynamic model of passenger for a biped walking vehicle. The walking pattern generation that enables stable walking even if passenger sits naturally is also described. The model consists of lower-limbs part assumed to be fixed to the robot, and the upper body assumed to be 1 particle with 2 DOF mounted on the seat via 2 springs and dampers. The parameters are identified through waist shaking experiments by using a force-torque sensor under the seat. The walking pattern generation method involves the proposed model being built onto a strict model of the robot, and through iteration computation, a stable walking pattern is generated. The effectiveness of the proposed method is confirmed through experiments