The transformation from high level task specification to low level motion control is a fundamental issue in sensorimotor control in animals and robots. This paper describes a control scheme called Virtual Model Control that addresses this issue. Virtual Model Control is a motion control language that uses simulations of imagined mechanical components to create forces, which are applied through real joint torques, thereby creating the illusion that the virtual components are connected to the robot. Due to the intuitive nature of this technique, designing a Virtual Model Controller requires the same skills as designing the mechanism itself. A high level control system can be cascaded with the low level Virtual Model Controller to modulate the parameters of the virtual mechanisms. Discrete commands from the high level controller would then result in fluid motion. Virtual Model Control has been applied to a physical bipedal walking robot. A simple algorithm utilizing a simple set of virtua...

Walking is an easy task for most humans and animals. Two characteristics which make it easy are the inherent robustness (tolerance to variation) of the walking problem and the natural dynamics of the walking mechanism. In this thesis we show how understanding and exploiting these two characteristics can aid in the control of bipedal robots. Inherent robustness allows for the use of simple, low impedance controllers. Natural dynamics reduces the requirements of the controller. We present a series of simple physical models of bipedal walking. The insight gained from these models is used in the development of three planar (motion only in the sagittal plane) control algorithms. The first uses simple strategies to control the robot to walk. The second exploits the natural dynamics of a kneecap, compliant ankle, and passive swing-leg. The third achieves fast swing of the swing-leg in order to enable the robot to walk quickly (1.25 m s ). These algorithms are implemented on Spring Flamingo...

Series Elastic Actuators have linear springs intentionally placed in series between the motor and actuator output. The spring strain is measured to get an accurate estimate of force. Despite using a transmission to achieve high force/mass and high power/mass, the spring allows for good force control, high force fidelity, minimum impedance, and large dynamic range. A second order linear actuator model is broken into two fundamental cases: fixed load -- high force (forward transfer function), and free load -- zero force (impedance). This model is presented with dimensional analysis and extends previous linear models to include friction. Using the model and dimensionless groups, we examine nonlinear e#ects of motor saturation as it relates to large force bandwidth and nonlinear friction e#ects such as stiction. The model also helps to clarify how the springs help and hinder the operation of the actuator. The information gained from the model helps to create a design procedure for Series...

Simple intuitive control strategies can be used to compel bipedal robots to walk over sloped terrain. We describe an algorithm for walking dynamically and steadily over sloped terrain with unknown slope gradients and transition locations. The algorithm is developed based on geometric considerations. The overall algorithm is very simple and does not require the biped to have an extensive sensory system for walking over moderate slopes. The ground is detected blindly using only foot contact switches. Using a few simple strategies, we have compelled a 7 link planar biped simulation to walk up and down slopes and over rolling terrain. 1 Introduction We have successfully used Virtual Model Control to control a planar biped to walk on flat ground [4,5]. Since rough terrain locomotion is important for legged locomotion, this motivates us to apply Virtual Model Control for rough terrain locomotion of a biped. Zheng and Shen [7] achieved control of a static biped to walk on an unknown sloped ...

We present the design and construction of Mertz, an active-vision humanoid head robot, with the immediate goal of having the robot runs continuously for many hours a day without supervision at various locations. We address how the lack of robustness and reliability lead to limitations and scalability issues in research robotic platforms. We propose to attend to these issues in parallel with the course of robot development. Drawing from lessons learned from our previous robots, we incorporated various fault prevention strategies into the electromechanical design. We have implemented a preliminary system, integrating sensorimotor, vision, and audio in order to test the full range of all degrees of freedom and enable the robot to engage in simple visual and verbal interaction with people. We conducted a series of experiment where the robot ran for 82 hours within 9 days at different public spaces. The robot interacted with a large number of passersby and collected at least 100,000 face images of at least 600 individuals within 4 days. We learned various lessons involving the robustness of current design and identified a set of failure modes. Lastly, we present the long term research direction for the robot.

A simplified cartesian computed torque (SCCT) control scheme and its application to an experimental climbing robot named LIBRA is presented. SCCT control is developed exploiting some of the characteristics of highly geared mobile robots. The effectiveness of the method is shown by simulation and experimental results using the LIBRA robot. SCCT control is shown to have improved performance, over traditional Jacobian Transpose Control, for the LIBRA multilimbed robot. 1. INTRODUCTION There is an increasing need for mobile robots to perform tasks such as space exploration, nuclear site cleanup, bomb disposal, and infrastructure inspection and maintenance [1-3]. To function in these unstructured environments, the capabilities of multilimbed robots are desirable. However, the use of multilimbed robotic systems has been limited for a number of reasons including the fact that multilimbed systems can be difficult to control in unknown or partially known rugged environments. Effective control ...

Robot manipulation tasks in unknown and unstructured environments can often be better addressed with hands that are capable of force-sensing and passive compliance. We describe the design of a compact four degree-of-freedom (DOF) hand that exhibits these properties. This hand is being developed for a new humanoid robot platform. Our hand contains four modular Force Sensing Compliant (FSC) actuators acting on three fingers. One actuator controls the spread between two fingers. Three actuators independently control the top knuckle of each finger. The lower knuckles of the finger are passively coupled to the top knuckle. We place a pair of torsion springs between the motor housing and the hand chassis. By measuring the deflection of these springs, we can determine the acting force of the actuator. The springs also provide compliance in the finger and protect the motor gearbox from high impact shocks. Our novel actuators, combined with embedded control electronics, allow for a compact and dexterous hand design that is well suited to humanoid manipulation research. 1

Since robots are typically designed with an individual actuator at each joint, the control of these systems is often difficult and non-intuitive. This thesis explains a more intuitive control scheme called Virtual Model Control. This thesis also demonstrates the simplicity and ease of this control method by using it to control a simulated walking hexapod. Virtual Model Control uses imagined mechanical components to create virtual forces, which are applied through the joint torques of real actuators. This method produces a straightforward means of controlling joint torques to produce a desired robot behavior. Due to the intuitive nature of this control scheme, the design of a virtual model controller is similar to the design of a controller with basic mechanical components. The ease of this control scheme facilitates the use of a high level control system which can be used above the low level virtual model controllers to modulate the parameters of the imaginary mechanical components. In...

This analytic and experimental study proposes a control algorithm for coordinated position and force control for autonomous multi-limbed mobile robotic systems. The technique is called Coordinated Jacobian Transpose Control, or CJTC. Such position/force control algorithms will be required if future robotic systems are to operate effectively in unstructured environments. Generalized Control Variables, GCV’s, express in a consistent and coordinated manner the desired behavior of the forces exerted by the multi-limbed robot on the environment and a system’s motions. The effectiveness of this algorithm is demonstrated in simulation and laboratory experiments on a climbing system.

Abstract — Physical humanoids often require the ability to maintain upright balance while performing various tasks involving locomotion and environmental interaction. Such balance requirements have been difficult to maintain with traditional approaches to articulated motion control. We claim that these difficulties are significantly due the use of parent-space in standard proportional-derivative (PD) servoing, typically requiring highly sophisticated decision making policies to function while maintaining balance. Using inspiration from inverted pendulum robots, we address humanoid balance control through a worldspace servoing model. Our model retains the same basic form as the PD-servo, but uses inertial/accelerometer measurements rather potentiometer-like sensing. Our humanoids are able to functionally balance, locomote, and recover without sophisticated decision making. We demonstrate the efficacy of our approach through simulation experiments involving locomotion, user interaction, ballistic motion, uneven terrain, and dramatic disturbances. I.