Ching-Long Shih

Asymptotically Stable Walking of a Five-Link Underactuated 3-D Bipedal Robot

This paper presents three feedback controllers that achieve an asymptotically stable, periodic, and fast walking gait for a 3-D bipedal robot consisting of a torso, revolute knees, and passive (unactuated) point feet. The walking surface is assumed to be rigid and flat; the contact between the robot and the walking surface is assumed to inhibit yaw rotation. The studied robot has 8 DOF in the single support phase and six actuators. In addition to the reduced number of actuators, the interest of studying robots with point feet is that the feedback control solution must explicitly account for the robots natural dynamics in order to achieve balance while walking. We use an extension of the method of virtual constraints and hybrid zero dynamics (HZD), a very successful method for planar bipeds, in order to simultaneously compute a periodic orbit and an autonomous feedback controller that realizes the orbit, for a 3-D (spatial) bipedal walking robot. This method allows the computations for the controller design and the periodic orbit to be carried out on a 2-DOF subsystem of the 8-DOF robot model. The stability of the walking gait under closed-loop control is evaluated with the linearization of the restricted Poincare map of the HZD. Most periodic walking gaits for this robot are unstable when the controlled outputs are selected to be the actuated coordinates. Three strategies are explored to produce stable walking. The first strategy consists of imposing a stability condition during the search of a periodic gait by optimization. The second strategy uses an event-based controller to modify the eigenvalues of the (linearized) Poincare map. In the third approach, the effect of output selection on the zero dynamics is discussed and a pertinent choice of outputs is proposed, leading to stabilization without the use of a supplemental event-based controller.

Asymptotically Stable Walking of a Simple Underactuated 3D Bipedal Robot

This paper presents a feedback controller that achieves an asymptotically stable, periodic, and fast walking gait for a 3D bipedal robot consisting of 3-links and passive (unactuated) point-feet. The robot has 6 DOF in the single support phase and four actuators. In addition to the reduced number of actuators, the interest of studying robots with point feet is that the feedback control solution must exploit the robots natural dynamics in order to achieve balance while walking. We use an extension of the method of virtual constraints, a very successful method for planar bipeds, in order to simultaneously compute a periodic orbit and an autonomous feedback controller that realizes the orbit, for a 3D (spatial) bipedal walking robot. This method allows the computations for the controller design and the periodic orbit to be carried out on a 2-DOF subsystem of the 6-DOF robot model. The linearization of the Poincare map of the closed-loop system proves that the achieved periodic walking motion, at a speed of approximately one and a half body lengths per second, is exponentially stable.

Fuzzy Sliding-Mode Underactuated Control for Autonomous Dynamic Balance of an Electrical Bicycle

The purpose of this paper is to stabilize the running motion of an electrical bicycle. In order to do so, two strategies are employed in this paper. One is to control the bikes center of gravity (CG), and the other is to control the angle of the bikes steering handle. As in general, the control of the CG applies a pendulum. An additional factor is the lean angle with respect to the gravitational direction of the bicycle in motion. In this total, the proposed system produces three outputs that will affect the dynamic balance of an electrical bicycle: the bikes pendulum angle, lean angle, and steering angle. Based on the data of input-output, two scaling factors are first employed to normalize the sliding surface and its derivative. According to the concept of the if-then rule, an appropriate rule table for the ith subsystem is obtained. Then, the output scaling factor based on Lyapunov stability is determined. The purpose of using the proposed fuzzy sliding-mode underactuated control (FSMUAC) is to deal with the huge uncertainties of a bicycle system often caused by different ground conditions and gusts of wind. Finally, the simulations for the electrical bicycle in motion under ordinary PID control, modified proportional-derivative control, and FSMUAC are compared to judge the efficiency of our proposed control method.

Force control and breakthrough detection of a bone-drilling system

Because neurosurgery and orthopedic surgery often require the drilling of bones, this paper attempts to solve the problem of bone drilling. The goal is to realize a control system that drills with a contact drilling force and can automatically stop drilling at the moment of breaking through. In particular, both the dc drilling motor control and the feed rate control are driven by force control in order to accommodate the system impedance. Moreover, breakthrough detection comes from to the threshold information of the thrust force as well as the trend of both the drilling torque and the feed rate. The proposed technique was experimentally verified through the drilling of pig bones, and the results are in accordance with the theoretical model both in the bone-drilling process and at the point of breakthrough.

From stable walking to steering of a 3d bipedal robot with passive point feet

This paper exploits a natural symmetry present in a 3D robot in order to achieve asymptotically stable steering. The robot under study is composed of 5-links and unactuated point feet; it has 9 DoF (degree-of-freedom) in the single-support phase and six actuators. The control design begins with a hybrid feedback controller that stabilizes a straight-line walking gait for the 3D bipedal robot. The closed-loop system (i.e., robot plus controller) is shown to be equivariant under yaw rotations, and this property is used to construct a modification of the controller that has a local, but uniform, input-to-state stability (ISS) property, where the input is the desired turning direction. The resulting controller is capable of adjusting the net yaw rotation of the robot over a step in order to steer the robot along paths with mild curvature. An interesting feature of this work is that one is able to control the robots motion along a curved path using only a single predefined periodic motion.

Fuzzy sliding-mode under-actuated control for autonomous dynamic balance of an electrical bicycle

The purpose of this paper is to stabilize the running motion of an electrical bicycle. In order to do so, two strategies are employed in this paper. One is to control the bikepsilas center of gravity (CG), and the other is to control the angle of the bikepsilas steering handle. In addition, the proposed system produces three outputs that will affect the dynamic balance of an electrical bicycle: the bikepsilas pendulum angle, lean angle, and steering angle. Based on the data of input-output, two scaling factors are employed to normalize the sliding surface and its derivative. According to the concept of if-then rule, an appropriate rule table for the ith subsystem is obtained. Then the output scaling factor based on Lyapunov stability is determined. The proposed control method used to generate the handle torque and pendulum torque is called fuzzy sliding-mode under-actuated control (FSMUAC). The purpose of using the FSMUAC is the huge uncertainties of a bicycle system often caused by different ground conditions and gusts of wind; merely ordinary proportional-derivative-integral (PID) control method or other linear control methods usually do not show good robust performance in such situations.

HZD-based control of a five-link underactuated 3D bipedal robot

This paper presents a within-stride feedback controller that achieves an exponentially stable, periodic, and fast walking gait for a 3D bipedal robot consisting of a torso, revolute knees, and passive (unactuated) point feet. The walking surface is assumed to be rigid and flat; the contact between the robot and the walking surface is assumed to inhibit yaw rotation. The studied robot has 8 DOF in the single support phase and 6 actuators. In addition to the reduced number of actuators, the interest of studying robots with point feet is that the feedback control solution must explicitly account for the robot¿s natural dynamics in order to achieve balance while walking. We use an extension of the method of virtual constraints and hybrid zero dynamics (HZD), a very successful method for planar bipeds, in order to determine a periodic orbit and an autonomous feedback controller that realizes the orbit, for a 3D (spatial) bipedal walking robot. The effect of output selection on the zero dynamics is highlighted and a pertinent choice of outputs is proposed, leading to stabilization without the use of a supplemental event-based controller.

Autonomous dynamic balance of an electrical bicycle using variable structure under-actuated control

In an electric bicycle, two strategies are taken up to stabilize the running motion of a bicycle. One is the control of its center of gravity (CG), and the other is the control of its steering angle of handle. In general, the control of the CG is used a pendulum. In addition, the motion of a bicycle often possesses a lean angle with respect to vertical direction. In this situation, the proposed system contains three outputs: steering angle, lean angle, and pendulum angle, these will affect the dynamic balance of an electrical bicycle. The proposed control generating the handle torque and pendulum toque is called variable structure under-actuated control (VSUAC). The motivation of using the VSUAC is that the system uncertainties of a bicycle are often huge due to different ground conditions and a gust of wind. Merely use an ordinary proportional-derivative-integral (PID) control or other linear controls often can not have good robust performance. Finally, the compared simulations for the electrical bicycle among ordinary PID control, modified proportional-derivative control (MPDC), and VSUAC confirm the usefulness of our proposed control.

Force control and breakthrough detection of a bone drilling system

Because neurosurgery and orthopedic surgery often require the drilling of bones, this paper attempts to solve the problem of bone drilling. The goal is to realize a control system that drills with a contact drilling force and can automatically stop drilling at the moment of breaking through. In particular, both the dc drilling motor control and the feed rate control are driven by force control in order to accommodate the system impedance. Moreover, breakthrough detection comes from to the threshold information of the thrust force as well as the trend of both the drilling torque and the feed rate. The proposed technique was experimentally verified through the drilling of pig bones, and the results are in accordance with the theoretical model both in the bone-drilling process and at the point of breakthrough.

Steering of a 3D bipedal robot with an underactuated ankle

This paper focuses on steering a 3D robot while walking on a flat surface. A hybrid feedback controller designed in [1] for stable walking along a straight line is modified so that it is capable of adjusting the net yaw rotation of the robot over a step in order to steer the robot along paths with mild curvature. The controller is designed on the basis of a single pre-defined trajectory for periodic walking along a straight line. In order to illustrate the role of internal/external (i.e., medial/lateral) rotation at the hip in achieving curved walking motions, the performance of two robots, one with internal/external rotation and one without, is compared.