An Adaptive Gait for Legged Walking Machines over Rough Terrain
Ching-Long Shih and Charles A. Klein
IEEE Transaction on Systems, Man, and Cybernetics, Vol. 23, No. 4, July/August 1993. pp. 1150 - 1155
Abstract - An adaptive gait algorithm for multilegged walking machines over rough terrain has been developed. The heuristic and hierarchical approach for the three levels of 1) body motion adaptation, 2) leg sequence adaptation, and 3) leg position adaptation is effective, straightforward, and relatively independent of the number of legs. On rough terrains with depressions the algorithm behaves like a "free gait"; on level ground terrain it behaves more like a periodic gait. The effectiveness of the proposed gait over rough terrains with depressions is demonstrated with several computer simulations.

Optimal Force Distribution for the Legs of a Walking Machine with Friction Cone Constraints
Charles A. Klein and Sakon Kittivatcharapong
IEEE Transactions on Robotics and Automation, Vol. 6, No. 1, February 1990. pp. 73 - 85
Abstract - An important problem for a legged vehicle with active force control is the allocation of forces at the feet to achieve a desired net force and torque on the body. In order to prevent leg slippage, foot forces must meet friction cone constraints. This problem is especially important when these vehicles have arms which also must interact with the environment. In the past, pseudoinverse and linear programming techniques have been proposed. This paper explores two new methods which can find solutions in more extreme conditions than is possible for the pseudoinverse method. The new methods also provide answers which have better temporal continuity than linear programming results do. A simple test identifies many cases where no solutions exist.

Vision Processing and Foothold Selection for the ASV Walking Machine
Charles A. Klein, Chin-Cheng Kau, Eric A. Ribble and Mark R. Patterson
Proceedings of SPIE, Vol. 852, Mobile Robots II, 5 - 6 November, 1987. pp. 195 - 201
Abstract - This paper presents the vision system and the algorithms used to process range data for terrain following of a legged walking machine. The vision system consists of a laser range-finder, a vision computer, a terrain elevation map, and a guidance computer. The range data generated by the laser range-finder are processed and converted into a 3-D representation by the vision computer in real time, and then the elevation information along with the time data are stored in the terrain elevation map. With the real-time elevation information in the map, the guidance computer can select the best footholds for the walking machine in order to maneuver over rough terrain.

Computer Coordination of Limb Motion for Locomotion of a Multiple- Armed Robot for Space Assembly
Charles A. Klein and Mark R. Patterson
IEEE Transaction on Systems, Man, and Cybernetics, Vol. SMC-12, No. 6, November/December 1982. pp. 913 - 919
Abstract - Robotics is expected to play an important role in the construction of large space structures. One possible system would be a multiple-armed manipulator vehicle which could use general-purpose arms to walk over the structure to a construction site and then use the arms for assembly. The simulation of locomotion of such a vehicle with arms modeled after a currently available industrial manipulator is described.

Interactive Computer Control of an Adaptive Walking Machine
R.B. McGhee, C.A. Klein, and C.S. Chao
1979 MIDCON Conference, Chicago, November, 1979
Abstract - This paper presents a description of the hardware and software systems used to achieve interactive computer control of locomotion in an experimental hexapod vehicle. This vehicle, believed to be the first such machine to successfully operate under full computer control, possesses three independently powered joints in each of its six limbs. Each joint provides position and rate feedback to the control computer and on one limb has been fitted with a vector force sensor. The control computer is responsive to input commands from a human operator regarding the desired vehicle speed and direction. This information is used to automatically synthesize and execute the limb segment motions needed to achieve the desired vehicle behavior. Real-time software to permit automatic adaptation of the vehicle gait to motion over uneven ground and to optimally distribute actuator torques so as to minimize the energy cost of locomotion is currently under development.

On the Role of Regulated Compliance in Manipulation and Locomotion Tasks Involving Closed Kinematic Chains
R.B. McGhee, C.A. Klein, and R.L. Briggs
Proceedings of First Yugoslav Symposium on Industrial Robots and Artificial Intelligence, Dubrovnik, Yugoslavia, September, 1979
Abstract - Conventional materials-handling application of industrial robots do not involve closed kinematic chains except at the beginning and the end of the programmed motion. Consequently, in such situation, robot joint torques and forces are uniquely determined by the prescribed trajectory of the end-effector. In contrast, assembly tasks, bilateral manipulation, and legged locomotion all involve closed kinematic chains capable of supporting internal torques and forces not related to the desired motion. This phenomenon can result in excessive energy expenditure, saturation of actuators, and even in structural damage to the robot limb or to the manipulated object. This problem can be resolved through the use of artificial compliance introduced by the robot control computer. This paper presents a mathematical formulation of this problem together with some experimental results obtained relative to the locomotion of a six-legged robot.

Multi-Limbed Locomotion Systems for Space Construction and Maintenance
Kenneth J. Waldron and Charles A. Klein
Presented at JPL Workshop, January 20-22, 1987.
Abstract - Multi-limbed locomotion systems operating in a "hand over hand" fashion are attractive for the construction and maintenance of large structures in space. They offer much greater energy efficiency as compared to thruster based mobility systems. They also free the designer of the structure form the necessity to incorporate tracks or other elements necessary for construction robots into his structural design. This type of locomotion system also offers great flexibility for handling unexpected situations such as structural failures. A well developed technology of coordination of multi-limbed locomotory systems is now available. This presentation will include results from a NASA sponsored study of several years ago. This was a simulation study of a three-limbed locomotion/manipulation system. Each limb had six degrees of freedom and could be used either as a locomotory grasping hand-holds, or as a manipulator. The focus of the study was kinematic coordination algorithms. The presentation will also include very recent results from the Adaptive Suspension Vehicle Project. The Adaptive Suspension Vehicle (ASV) is a legged locomotion system designed for terrestrial use which is capable of operating in completely unstructured terrain in either a teleoperated or operator-on-board mode. Future development may include autonomous operation. The ASV features a very advanced coordination and control system which could readily be adapted to operation in space. An inertial package with a vertical gyro, and rate gyros and accelerometers on three orthogonal axes provides body position information at high bandwidth. This is compared to the operator's commands, injected via a joystick to provide a commanded force system on the vehicle's body. This system is, in turn, decomposed by a coordination algorithm into force commands to those legs which are in contact with the ground. The individual leg controls are mode switched between a force control mode, when the foot is on the ground, and a position velocity mode when the foot is being returned. This form of control is attractive for space applications of multi-limbed systems, whether for locomotion or manipulation, since the weight appears only as one of the forces acting on the vehicle body and the coordination algorithms are set up to minimize generation of loads by limbs pushing against one another.

Use of Force and Attitude Sensors for Locomotion of a Legged Vehicle over Irregular Terrain
Charles A. Klein, Karl W. Olson, and Dennis R. Pugh
The International Journal of Robotics Research, Vol. 2, No. 2, Summer 1983. pp. 3 - 17
Abstract - A number of legged vehicles are being developed for their mobility characteristics over irregular terrain. One such vehicle is The Ohio State University Hexapod vehicle (OSU Hexapod). Recently, the vehicle has been modified so that it can successfully walk over uneven terrain. Each of the feet has been equipped with two semiconductor strain gauges to measure lateral forces and a piezoelectric load cell to measure vertical forces. A vertical gyroscope and pendulums for orientation sensing have also been added. The control of locomotion over rough terrain can be decomposed into two complementary control processes, attitude control and active compliance. Attitude control is used to maintain the body tilt in a desired orientation, and active compliance is used to provide a suspension system by distributing force loading among the legs. It has been found that optimal force setpoints for the active- compliance algorithm can be calculated in closed form. This paper discusses the sensing hardware and the control system needed for legged locomotion over irregular terrain. Experimental results are provided for both statically determinate and indeterminate hexapod gaits.

Real-Time Control of a Multiple-Element Mechanical Linkage with a Microcomputer
Charles A. Klein and John J. Maney
IEEE Transactions on Industrial Electronics and Control Instrumentation, Vol. IECI - 26, No. 4, November, 1979. pp. 227 - 234
Abstract - In real applications, many devices are highly nonlinear and are difficult to control effectively. Variabilities within the systems and strong external influences make the problem more difficult. One example is the control of electric motors driving elements of a mechanical linkage system such as in an industrial manipulator. By adding a microprocessor to the system, however, the system can be made to operate as if it was linear with a time constant determined by the designer. A method of thus linearizing the system is the so-called "sliding mode" control scheme in which the controller causes the system to follow a prescribed straight-line path in phase space. By applying two different control laws on opposite sides of this switching line, the system is said to be in "sliding" mode between the two individual laws. Advantages of the method include insensitivity to plant parameter variations, applicability to highly nonlinear systems, and simplicity. The capabilities of this method are demonstrated through the presentation of experimental results obtained with a three-degree-of-freedom linkage system using an IMSAI microcomputer for control. Both position and force control are demonstrated.

Use of Active Compliance in the Control of Legged Vehicles
Charles A. Klein and Randal L. Briggs
IEEE Transactions on System, Man, and Cybernetics, Vol. SMC-10, No. 7, July, 1980. pp. 393 - 400
Abstract - Often it is desirable to specify both position and force at the end effector of a manipulator system; however, when the system forms a closed kinematic chain both cannot be realized independently. Active compliance is a trade-off method that can be easily incorporated into the supervisory control philosophy which is often used to control complex man-machine systems. An example of such a system is the Ohio State University (OSU) Hexapod which is a legged walking vehicle. Active compliance is shown to be invaluable for allowing legged locomotion over irregular terrain.

Operational Experience with the Adaptive Suspension Vehicle
K.J. Waldron, C.A. Klein, D. Pugh, V.J. Vohnout, E. Ribble, M. Patterson, and R.B. McGhee
Theory of Machines and Mechanisms, Proceedings of the 7th World Congress, 17-22 September, 1987, Sevilla, Spain, Vol. 3, pp. 1495 - 1498
Abstract - The Adaptive Suspension Vehicle is a legged locomotion system which uses computer coordination and advanced sensing to operate in rough terrain. This presentation will review the results of a program of testing and software installation which has occupied the calendar year of 1986. The paper will also contain a review of the major features of the mechanical and electronic hardware architectures, and the control and coordination software.

Design of a Multimicroprocessor-Based Controller Using a Structured Design Approach
C. Barrientos and C.A. Klein
IEEE Transactions on Industrial Electronics, Vol. IE-31, No. 4, November, 1984. pp. 292 - 298
Abstract - As automatic industrial devices become more and more sophisticated, increasingly complicated problems are involved in their design and testing, especially in systems such as dedicated multimicroprocessor-based controllers. Failure to address the complexities of such systems before the prototype stage can result in exceedingly lengthy redesigns and frustration, if not impossible, preproduction testing. A structured approach to both the design and testing of a complex robotic controller has been used to decompose the design/test task into manageable subtasks. Applying the approach to a legged locomotion case study has demonstrated that the structured method helps to anticipate design and testing problems by shifting effort toward the initial stages.

Force Interaction and Allocation for the Legs of a Walking Vehicle
Charles A. Klein and Tae-Sang Chung
IEEE Journal of Robotics and Automation, Vol. RA-3, No. 6, December, 1987. pp. 546 - 555
Abstract - Force is often used in the control of the legs of a walking machine to allow a vehicle to adapt to terrain irregularity. However, interaction in force among the legs have the capability of causing control system instabilities if not properly treated. Different criteria for allocating forces to the legs of a walking machine are considered, properties of force-induced instability modes are studied, and the plan of hybrid control allocated by legs as a means of avoiding these force interaction modes without requiring an excessively high control frequency is introduced.

Automatic Body Regulation for Maintaining Stability of a Legged Vehicle During Rough-Terrain Locomotion
Dominic A. Messuri and Charles. A. Klein
IEEE Journal of Robotics and Automation, Vol. RA-1, No. 3, September, 1985. pp. 132 - 141
Abstract - The evolution of legged vehicles has progressed significantly in recent years. These vehicles offer the potential of increased mobility for traversing rough terrain. The ability to maintain stability is an important consideration in the development of any control algorithm for a legged vehicle. Previous work on legged vehicle control generally assumes that the terrain is regular enough that only minimal operator interaction is necessary. However, for very irregular terrain the operator may require a guidance mode that gives maximum resolution and flexibility in controlling body, leg, position, and orientation. Several automatic body regulation schemes that aid the operator in this important task are described. A major development is the use of an improved stability measure which can be automatically optimized. This measure, together with a consideration of constraints on the kinematic limits of individual leg, leads to the development of schemes for automatic body regulation. The automatic body regulation schemes are incorporated into the vehicle control algorithm to provide a high degree of vehicle maneuverability while reducing the operator's burden.

Use of a Multiprocessor for Control of a Robotic System
Charles. A. Klein and Weerakiat Wahawisan
The International Journal of Robotics Research, Vol. 1, No. 2, Summer 1982. pp. 45 - 59
Abstract - In the control of robotic systems, multiprocessors have a number of potential advantages over single-processor configurations. These advantages include the possibility of modular future expansion, increased speed, and fault tolerance. This paper describes both the hardware and software design of a multiprocessor system and its use in controlling the OSU Hexapod vehicle, a complex robotic system. With the design of an inexpensive, high-density, eight-channel parallel line unit (PLU), it is possible to link five LSI-11 processors in a fully connected configuration. This configuration is very valuable for experimentation, since trials of tree, star, and loop structures can be made by simply ignoring links that are not needed. First, a tree structure is used to implement a hierarchical control algorithm run on a previously used uniprocessor system. Next, fault-tolerant features are added so that failed units are automatically replaced by spare units or, if all spares are in use, the necessary tasks are covered by the central processor, with a decrease in servoing frequency. To decentralize control to improve overall reliability, a ring structure is also used. If a processor fails, the ring is automatically reconfigured to isolate the faulty unit. Another application for the multiprocessor in the control of the OSU Hexapod vehicle is for real-time optimization of leg tip forces. This task demonstates the usefulness of the multiporcessor in a task that is not strictly parallel in form.