Capacitive transducers

The theory, applications, and possible structural designs of capacitive transducers are presented. Emphasis is placed on the circuits used in connection with the sensors, such as AM, FM, resonant circuits, mode circuits, direct current circuits, and special circuits. Some criteria for selection of a design or the purchase of a commercial device are given

Criteria for the Choice of a Capacitive Device for Mechanical Measurements

The advantages and disadvantages of different models of capacitive transducers and of various signal conditioning circuits are discussed with particular emphasis on the field of applications. A practical example of a design procedure is discussed

Two examples of applications of Kalman filtering to integrated systems of navigation

Two applications of optimal stochastic filters to navigation systems are described. The first is an air navigation system consisting of an inertial device (INS) and a Loran, plus an altimeter. The second is an application to a system of submarine navigation consisting of an inertial device (SINS) and an Omega plus a depth sensor

Hybrid computers and simulation languages in the study of dynamics of continuous systems

A comparison is presented of the use of hybrid computers and simulation languages as a means of studying the behavior of dynamic systems. Both procedures are defined and their advantages and disadvantages at the present state of the art are discussed. Some comparison and evaluation criteria are presented

Viking Thrust Vector Control Dynamics Using Hybrid Coordinates to Model Vehicle Flexibility and Propellant Slosh

Control System Design Implementation of the linear feedback control system with time varying feedback gains and command forces may be accomplished with a fairly simple analog controller. The feedback gains and command forces consist of well behaved sinusoidal functions, constants, and simple ramp functions. The difficulty caused by the gain fluctuation near the simulation final time may be overcome by cycling the control gain functions back to the beginning before the fluctuations take place. Cycling the control gain functions is not a problem because the control is in a feedback form. The effect of cycling the control gain functions may be interpreted in the analysis as restarting the nonlinear simulation with an initial state closer to the final state. Simulation of the nonlinear system within the region of operation always resulted in a stable response so the effect of restarting the simulation when the system state has moved closer to the final state is valid. A consequence of cycling the control is that the functional in Eq. Conclusions This study has shown that the dynamic instability caused by sloshing fluid stores carried in the main rigid body of a spacecraft may be controlled by use of a linear quadratic regulator with the fluid modeled as an equivalent spherical pendulum and only the first mode of fluid oscillation included. The control system presented stabilized a highly nonlinear system for a large deviation from the nominal operating point and uses easily measured state variables (only main body fixed angular rates and attitude) and was shown to be stable for a wide variation in fluid level. It was shown that sensing the dynamic state of the fluid was not necessary for the specific spacecraft under study. A pointing maneuver was also successfully accomplished by this control system and a control design based on the analysis was outlined for the specific spacecraft. Acknowledgments This study was completed under partial support of contract no. AFOSR-86-0080 and subcontract 83RIP33, U.S. Air Force. The authors wish to acknowledge the support of Iowa State University in accomplishing the lengthy digital computer simulation required in this study. References Introduction An interesting problem in robotics is cloth handling. Applications include composite lay-up and apparel and upholstery manufacturing. Rebman (1986) describes an application of a tactile sensor to assembly of a flexible diaphram and a plastic cap. Hertzanu and Tabak (1986) described an adaptive controller for an industrial sewing machine. For most applications, cloth must be held taut and unwrinkled. It was postulated that this requires multi-axis force control, and a suitable control system was designed and constructed. The system chosen is an adaptive force feedback loop with position accommodation. Non-adaptive force feedback control schemes have been described and tested by many researchers, such as Whitney (1977). An adaptive force feedback loop for coordination of two robot arms was described by Because cloth stiffness varies depending on whether the individual cloth fibers are taut or slack, a nonadaptive loop is unsuitable for cloth handling. An adaptive control loop was designed with cloth stiffness as the adaptive variable. The system design was constructed and tested using a PUMA 560 robot with a LORD 15/50 force/torque sensor mounted on its wrist. Control System Description The parameter estimator is a least mean square (LMS) estimator. Let y=KH(z)u = K a x z ' + + a"z~ -r-"u, \+b x z + ... +b"z~ where a it ..., a" and b\ b" axe found from the ordinary least squares plant identification, y is the error in the force, and u is the position command. Then the LMS estimator for A-is K* =K*^i+r{y-y*)w-l , where K* is the estimated stiffness, +a"u""), and Vf_ 1 =ff 1 «_ 1 + The position control law is where u, is the change in the position of the /th degree of freedom (DOF), y t is the force (or torque) error of the ith DOF, and K* is the stiffness of the rth DOF. end of a cloth of dimensions 36 by 36 in., the other end of which was attached to a table. Both ends of the cloth were stapled to wooden rods; proper robot end effectors would eliminate the need for these rods. Two 8086 microprocessor cards were also built. The 1st microprocessor calculated the cloth stiffness and end effector position changes; the 2nd microprocessor was used for communication with the robot and the force/torque sensor. Experimental Procedure The experiments were run with one end of the cloth fixed. The initial slack and misalignments of the cloth were as follows: Stretch (x) direction Lateral (y) direction 6 direction 6 to 10 in. of slack 2 to 4 in. of misalignment 5° to 20° of misalignment The robot straightened out the misalignments and pulled 4 lb of tension on the cloth. After it had done so the end effector was moved inward to produce 6 in. of slack in the x-direction. This movement draped the cloth over 2 boxes without wrinkling. Test Setup Experimental Results The visual results showed consistency between the experiments. In all of them, the cloth was successfully draped over the boxes without wrinkles, the motion was smooth, and the times were approximately the same. Transactions of the ASME position, the robot pulls a 4 lb tension on the cloth and adjusts the lateral (y) force and the moment to zero. This requires approximately 12 s. At 14 s the robot drapes the cloth; at this point the tension (x-force) falls to zero. This experiment was successfully repeated several times. Conclusions A force feedback control loop implemented on a robot has been used successfully to straighten and draw a tension on a cloth. Further work will include using more sophisticated end effectors to grip the cloth, and applications in upholstery and composite manufacture. Reference