LITERATURE ON CAPACITIVE SENSING HBB 6/24/96 MAUER 89 An End-Effector Based Imaging Proximity Sensor, Georg F. Mauer, Journal of Robotic Systems, 1989, pp301-316, Wiley & Sons. Built a 4x4 capacitive array for use as an end-effector sensor below 2 mm range. Developed equations for capacitance vs. distance and compared to experiments. Showed attenuation of image sharpness. Used capacitive bridge driven at 1 mhz. Elements switched on one at a time to eliminate cross-talk. Output signal approx. logarithmic with distance. FRANKLIN 77 U.S. Patent #4,099,118, Electronic Wall Stud Sensor, Robert C. Franklin, 1977 NOVAK 93 Jim L. Novak and Dan Schmitt, Closed-Loop MAST System Eyes Robotic Manufacturing, Sandia Technology Bulletin, December, 1993. Multi Axis Seam Tracker uses multiple, small capacitive sensors to guide robots along seams, edges or other constant-cross-section shapes. Developed for guiding a robot for paste-brazing rocket exhaust cooling tubes. SCHMITT 94 Dan J. Schmitt, Jim L. Novak, Gregory P. Starr and John E. Maslakowski, Real-Time Seam Tracking for Rocket Thrust Chamber Manufacturing, 1994 IEEE Robotics and Automation Proceedings. Developed capacitive sensor to automate seam tracking for precisely dispensing brazing paste at up to 100 mm/sec. Sensor has 4 capacitive electrodes and allows determination of x-y position and orientation. Tracking errors for the closed-loop robot system on the order of 0.2-0.6 mm, depending on speed (50-200 mm/sec). LUO 93 Ren C. Luo and Zhenhai Chen, An Innovative Micro Proximity Sensor, Proceedings of the 1993 JSME Intl. Conf. on Advanced Mechatronics, Tokyo, August, 1993, pp 621-625. Analyzed and built micro sensors based on principle of capacitive fringing: field between two adjacent electrodes is disturbed by the presence of conducting or non-conducting objects. Sensor size 1 mm square. Sensing range about 200 microns. Capacitances about .05 pF. No discussion of electronics. CHEUNG 89 Edward Cheung and Vladimir Lumelsky, Development of Sensitive Skin for a 3D Robot Arm Operating in an Uncertain Environment, IEEE, 1989 Developed a sensing skin for robot arm utilizing 500 reflective optical (IR) sensors. Sensors are time multiplexed and driven at different frequencies to prevent cross-talk. Output depends on the color, size and shape of the object. Light is modulated in range of 67-135 khz. Sensing range 3-10 inches. KOTHARI 88 M. Kothari, J.G. Webster, W.J. Thompkins, et al, Capacitive Sensors for Measuring the Pressure Between the Foot and Shoe, IEEE Engineering in Medicine & Biology, 10th Intl. Conf., 1988. Utilized commercial load sensor(Hercules model F4-4R) to measure foot force for gait analysis. Built frequency measuring circuit to sense force. Capacitance range 230-460pF, pressure 0-1.3 MPa. STUCKMAN 89 B.E. Stuckman, G.R. Zimmerman and C.D. Perttunen, A Solid State Infrared Device for Detecting the Presence of Car in a Driver's Blind Spot, Proceedings of the 32nd Midwest Symposium on Circuits and Systems, Champaign, IL, August, 1989 An active IR sensor was built and tested to detect vehicles 3-12 feet away in the blind spot. Reflected signal was affected by car color (white best, black worst); angle of incidence (perpendicular best); height. Not clear how beam was modulated. SIMMONS 94 I.M. Simmons, Automotive Applications of Millimetre Wave Radar, IEE Colloquium on Exploiting the Millimetre Wave-bands, London, January, 1994. Discusses applications for millimetre wavelength radar (e.g. 70-90ghz) for automotive applications: intelligent cruise control, speed sensors, parking aids, ground height sensor, blind-spot detectors, obstacle detection. ICC is where most work is currently centered. Frequency 76-77ghz allocated for auto radar in Europe. High frequency allows size reduction and wide frequency band (because of air frequencies available). Attenuation doe to rain or fog not problems at short ranges. Low cost is major factor for auto applications. Blind spot sensor with 5 m range should be easy to do. HOLPP 94 W. Holpp, Automotive Radars for Advanced Road Traffic Safety, Proceedings of Microwave and Millimetre Wave Technologies, London, October, 1994 New technologies are making millimetre radar (30 ghz and above--1 cm and shorter) attractive for automotive applications. Potential applications include ground-speed msmt., auto cruise control, collision avoidance, road-condition assessment, and traffic data acquisition. AEG, Bosch and Phillips have worked on collision avoidance radar systems around 77 ghz. FM/CW widely used rather than pulsed. Good technical details of various systems. WAI 87 W.O. Wai, Blind Spot Monitor, Sixth Intl. Conference on Automotive Electronics, London, October, 1987. Failure of drivers to be aware of vehicles in their blind spots has resulted in many accidents. Turning to check blind spot takes the drivers attention from things ahead. A passive, 2-element IR system was tested that relies on higher relative temperature of passing vehicles, esp. the engine area. Used logic to determine whether vehicle is overtaking or passing in opposite direction. Electronic circuits shown, but little technical detail on operation or results. BIMAN 91 D. Biman, Proximity Matrix Sensor Image Processing, Robot Control 1991, (SYROCCO '91), Third IFAC/IFIP/IMACS Symposium, Vienna, Austria, September, 1992, pp 519-524. Overview of proximity sensing technologies for robot end-effectors: inductive, ultrasonic, photoelectric, magnetic, capacitive. Build two prototype sensors with 8x8 elements, sensing capacitance to ground. Elements were square on flat surface. Discussion of image processing algorithms for orientation and position, edge detection. WEGERIF 92 D. Wegerif and D. Rosinski, Sensor Based Whole Arm Obstacle Avoidance for Kinematically Redundant Robots, Sensor Fusion V, SPIE, Boston, November, 1992, vol. 1828 pp 417-426. Authors at Merritt Systems, Inc. built a system using 49 reflective optical sensors to cover a 3-link SCARA arm (ala Cheung and Lumelsky). IR LEDs were modulated with square waves of 37.5, 75 and 150 khz for the three links. Received signal was demodulated and low-pass filtered at 10 khz, giving settling time of 0.25 msec. Three links were monitored at 30 hz through 3 separate A/D channels. They used standard IREDs and PIN diodes. These were plugged into ribbon-cable connectors crimped onto 50-conductor ribbon-cable. Targets were reflective. They also compared optical, ultrasonic and capacitive sensors. They found optical and ultrasonic sensors detected objects 4-6 inches away; capacitive about 3 inches. Recommend combined IR and ultrasonic system. KARLSSON 94 N. Karlsson, Theory and Application of a Capacitive Sensor for Safeguarding in Industry, Proceedings of IEEE Instr. and Msmt. Technology Conf.--IMTC 94, Hammamatsu, Japan, May, 1994. A capacitive sensor was built and tested to detect entry of persons into a robot work cell with a floor area of 9 sq. meters. Sensor comprises floor and ceiling electrodes, 2 m apart, driven at 1.25 v at 50 khz. Sine wave signal is "modulated by bandwidth limited white Gaussian noise" (?); lock-in amplifier makes it possible to detect the signal among noise. Signal for one person apx. 250 mv; noise (including robot motions) about 20 mv. Electric field is about 440 mv/m, below the guideline of 2.5 v/m for visual display units. Signal was about 500 mv for 2 people in area. NERINO 95 R. Nerino, Capacitive Sensor Arrays in Dimensional Analysis of Surfaces, IEEE Trans. on Instr. and Msmt., vol. 44, no. 4, pp 875-80, August, 1995. Theoretical study of using capacitive sensing for measuring smoothness and flatness of surfaces on sub-micron level. Propose a 3-element linear array (for linear, not surface, msmts.) to determine surface profile. Gap is assumed small compared to surface wavelengths, and sensor size small compared to gap. NOVAK 92 J.L. Novak and J.T. Feddema, A Capacitance-Based Proximity Sensor for Whole Arm Obstacle Avoidance, 1992 IEEE Proceedings of the Intl. Conf. on Robotics and Automation. Capacitive sensors have advantages over others for proximity sensors: broad coverage, instantaneous sensing, simple sensor construction, operation in hostile environments, insensitivity to surface characteristics. Use two, side-by-side plates and measure capacitance between them via charge amplifier. Guard not needed, and signal lines can be unshielded, they claim. They used 8-element sensor array to cover an arm; sensitive to 16 inches. Charge amplifier senses only changes in mutual capacitance. Used sensors 15 mm long with gaps from 3 mm to 108 mm between the plates. (What is length in other dimension?) Operating frequencies 100 and 158 khz. Lots of technical details. FEDDEMA 94 J.T. Feddema and J.L. Novak, Whole Arm Obstacle Avoidance for Teleoperated Robots, 1994 IEEE Robotics and Automation Proceedings. Use WHAP (Whole Arm Proximity) sensors to cover Puma 560 robot for obstacle avoidance. Each sensor comprised a 20 mm dia button surrounded by a 30 mm ID x 38 mm OD ring made on 3-layer PCB. Used 49 sensors to cover arm. C-C distances for sensors ranged from 50-120 mm to provide complete coverage. Sensor range apx. 330 mm using flat metal target. Discussion of arm control scheme. NOVAK 91 J.L. Novak and J.J. Wiczer, A High Resolution Capacitive Imaging Sensor for Manufacturing Applications, Proceedings of the 1991 IEEE Intl. Conf. on Robotics and Automation, Sacramento, CA, April, 1991. Analyzed and built small sensor for measuring burrs. Sensor uses two .020" diameter electrodes with .010" gap between them. Allows inspection during the deburring operation. Mutual capacitance between the side-by-side elements decreases (?) when other obstacles "shield" the field. Used a "synchronous detection scheme" comprising a mixer driven by a carrier signal generated by the original oscillator. AC noise equivalent to 2 aF (.002 pF) or 5 ppm. Repeatability on the order of microns with object ~500 microns from sensor. NOVAK 89 J.L. Novak, Initial Design and Analysis of a Capacitive Sensor for Shear and Normal Force Measurement, 1989 Proc. of the IEEE Robotics and Automation Conf. Analyzed and built a capacitive sensor for measuring shear and normal forces on an elastomeric pad. Used differential capacitance in shunt mode. Sensor was about 2.5 mm square.Forces in the range of 1 pound, capacitances ~1pF. PUERS 93 Robert Puers, Capacitive Sensors: When and How to Use Them, Sensors and Actuators A, 37-38 (1993) 93-105. Capacitive sensors for pressure and acceleration measurement have advantages over more common piezoresistive sensors: high sensitivity, low power, smaller temp. effects and drift, simple sensor element. Measure displacement not strain. Discussion of various sensor configurations; overview of devices being developed. VON DER EMDE 93 Gerhard von der Emde, The Sensing of Electrical Capacitances by Weakly Electric Mormyrid Fish: Effects of Water Conductivity, Journal of Exp. Biology, vol. 181, 157-173, 1993. African Mormyrid fish can distinguish capacitive and resistive objects and "electro-locate" objects. An electric organ in the tail creates an electric field around the body that is measured by epidermal electro-receptor organs. This is useful in distinguishing living objects--which possess capacitive components--from non-living. LI 94 X.J. Li and G.C.M. Meijer, A Novel Smart Resistive-Capacitive Angular PSD, 1994 IEEE Instrumentation and Msmt. Technology Conf. Authors developed a novel potentiometer that replaces the sliding contact with a capacitive coupling. Appropriate circuitry is developed to obtain a period-modulated signal that can be read directly by a micro-controller. KIRKBY 89 D.R. Kirkby, P.J. Hillson and C.A. Mosse, Capacitance Sensing Drop Counter, Journal of Biomedical Eng., vol. 11, March, 1989, pp 166-69. Developed a drop counter to replace optical counters used parenteral infusion. Reliable drop counting by capacitance measurement from ring that clips on outside of tube. Insensitive to ambient light. BRAMANTI 90 Mauro Bramanti, A High Sensitivity Measuring Technique for Capacitive Sensor Transducers, IEEE Trans. on Industrial Electronics, vol. 37, no. 6, December, 1990. A technique is proposed for measuring low-level capacitance changes (e.g. less than 1 pF). The test capacitance is part of a resonant LRC circuit with high Q (low damping). Analysis shows that the phase shift of the output relative to the circuit excitation is the product of the relative change in capacitance and the circuit Q. HIGHWAY COLLISION AVOIDANCE LITERATURE: YOUNG 95 Stephen K. Young, Collision Avoidance System Performance for Lane Change, Merging and Backing: Phase I Results and Future Plans, prepared for U.S. Dept. of Trans., National Highway Traffic Safety Administration, October 27, 1995. Phase I of the study by TRW on crash avoidance systems (CAS). Four year effort initiated in 1993 to develop CAS. Phase I tasks to analyze the problem, test existing hardware (commercial or in development) and establish prelim. performance specs. Defined 8 categories of lane change/merge crashes. In 86% of these cases, no driver crash avoidance maneuvers were indicated, suggesting driver inattentiveness and potential for warning systems. In 58%, closing speeds were less than 5 mph, where "blind-spot" monitor would probably be useful. Goals for backing CAS include detection of obstacles near rear of vehicle; detection of crossing-path pedestrians, cyclists, vehicles; detection of crossing-path backing vehicles in forward path of subject vehicle. Tested 11 existing CAS including acoustic, radar and electro-optical. Most simple proximity detectors (<5 m). Latencies 40-1900 msec. Recommended performance specs: Detect potentially conflicting vehicles before/during lane changes by subject vehicle Warn drive in time to avert collision or reduce severity ... Operate in all weather, day and night. Cost not critical at this stage, but is considered. Key performance specs. of the blind-spot detector: 3.7 m (1 lane) to L or R, 1 vehicle length fwd/back, 0.3-3 m high Targets: bike to truck Latency: <500 msec Accuracy: 0.6 meter Prob of detection: > 0.99 MECHENG 92 Fiber Optics Eliminate Driver's Blind Spot, Mechanical Engineering, November, 1992, p20. Fiber optic system has been patented by HAS Group, Inc. (San Jose, CA) which provides a flexible, passive rear view for the driver. Fiberview is commercially available for about $200, but price could drop to $18 in quantity. It uses to coherent fiber bundles to transmit images from two lens assemblies to a single viewer: the two images are merged to provide a single, panoramic scene. Claimed to provide clearer image than video cameras, esp. in poor lighting, and to be more reliable. POPSCI 95 Lane Changing, Confidently, Popular Science, June, 1995. Unintentional side-swiping accounts for about 14% or highway collisions. Side-Minder is an active IR system developed by Optoelectronics Division of Siemens Corp. (Cupertino, CA) that alerts drivers of the presence of vehicles in the blind spot. A cluster of IR emitters and detectors in the tail light looks for vehicles in the blind spot. A yellow warning light appears on the side mirror when a vehicle is detected. Main development problem was sensing over the range of car colors-- 6 sensors are used each side to receive reflections from curved body panels. Must receive 14 positive signals in .05 sec. to give alarm. Works in rain or snow. Could cost as little as $50/car as original equipment. ELEC 94 George Taninecz, System Brings Vision to Auto Blind Spots, Electronics, 24 October, 1994, p11. Side-Minder (see POPSCI 95 above) monitors blind spots on both sides of car, covering the area from 3 ft. ahead of the rear bumper to 9 ft. behind, and 9 ft. laterally (about 1/2 lane). Uses 6 LEDs and 6 photo detectors monitored by ASIC. If 7 consecutive pos. signals received in 20 msec, ASIC checks for a repeat sequence then warns the driver. A blue LED on the side mirror indicates system operation; 3 blinking, yellow LEDs indicate an alarm. System self-checks every 1.2 sec, and warns of improper operation if sensor is dirty. May use heater to clear frost and moisture. Should be available for 97 or 98 model vehicles at $50 or less. POPSCI 94 Rest Those Neck Muscles, Popular Science, September, 1994. Spartan Corp. (Jackson, MI) is developing an acoustic sensor that mounts in a car's side mirror housing and scans the blind spot when the turn signal is activated. A red light glows in the mirror to indicate a vehicle present. Muth Advanced Technologies (Sheboygan, WI) is developing the mirror unit, with variable intensity warning lamp that adjusts for ambient light levels.