Paul E. Sandin - Robot Mechanisms and Mechanical Devices Illustrated (779750), страница 46
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This design has great simplicity and reliability. In a car, the leafspring performs the task of springs, but it also holds the axles in place,with very few moving parts. The usual layout on a car has one endattached to the frame through a simple pivot joint and the other endattached through either a pivoting link, or a robust slot to allow for thatend to move back and forth in addition to rotating. The center of thespring is attached to the axle, allowing it to move up and down but not inany other direction. Two springs are required to hold the axle horizontal.286Chapter 11Proprioceptive and Environmental Sensing Mechanisms and DevicesFigure 11-16 Horizontaloose footed leaf springThe leaf spring can also be used to suspend a robot’s bumper quiteeffectively by turning the spring on its side and attaching the center tothe chassis and each end to points on the bumper.
One end, or both, stillneeds to be attached through a slot or pivoting link, but the result is stillvery simple and robust. This layout can be used on larger robots also,since the leaf spring is an efficient suspension element even in largersizes.For robots that must detect bumps from the rear, it may be possible touse a single spring to support an entire wrap around bumper. If thiswould produce a cumbersum or overly large spring, the sideways-leafspring layout can be enhanced by adding a second spring to further support the rear of a one-piece wrap around bumper. Figure 11-16 shows asingle slot sideways leaf spring layout.Sliding Front PivotDesigning a bumper suspension system based on the fact that the bumperneeds primarily to absorb and detect bumps from the front produces asystem which moves easily and farthest in the fore-and-aft directions,but pivots around some point in the front to allow the sides to movesome.
The system could be called a sliding front-pivot bumper suspension system (Figure 11-17). Sliding joints are more difficult to engineerthan pivoting or rotating joints, but this concept does allow large motionsChapter 11Proprioceptive and Environmental Sensing Mechanisms and Devices287Figure 11-17 Sliding front pivotin the most important direction. Springing it back to its relaxed positioncan be tricky.Suspension Devices to Detect Motionsin All Three PlanesThe V-groove device can be applied to 3D layouts as well, simply bymaking the V-block angled on top and bottom, like a sideways pyramid.A mechanical limit switch can be placed so that any motion of the Vblock out of its default position trips the switch. For even more sensitivity, the V-block can be made of rollers or have small wheels on its matingsurfaces to reduce friction.The simplest suspension system that allows motion in three directionsrelies on flexible rubber arms or compliant mounts to hold the bumperloosely in place.
These flexible members can be replaced with springsand linkages, but the geometries required for 3D motion using mechanical linkages can be complex. Figure 11-18 shows a layout for an elastomer or spring-based system. A well-sprung bumper or bumper/shell288Chapter 11Proprioceptive and Environmental Sensing Mechanisms and DevicesFigure 11-18 Vertical flexiblepost bumper suspensionthat uses one of these layouts can be used with no hard centering systemby using the “limit switch as hard stop” concept discussed previously.The bumper is sprung so that its relaxed position is just off the contactsof three or more switches.
This system is simple and effective for smallerrobots and a very similar layout is used on the popular Rug Warriorrobot.For larger designs, where the flexible post would need to be too big,compression springs can be used instead. A clever designer may even beable to size a single-compression spring layout that would be simpleindeed. The system can be designed to use the springs in their relaxedstate as springy posts, or, for larger forces, the springs can be slightlycompressed, held by internal cables, to increase their centering force andmake their default position more repeatable.Chapter 11Proprioceptive and Environmental Sensing Mechanisms and DevicesCONCLUSIONThe information you’ve just read in this book is intended for those interested in the mehanical aspects of mobile robots. There are, of course,many details and varieties of the mobile layouts, manipulators, and sensors that are not covered—there are simply too many.
It is my sincerehope that the information that is presented will provide a starting pointfrom which to design your unique mobile robot.Mobile robots are fascinating, intriguing, and challenging. They arealso complicated. Starting as simply as possible, with a few actuators,sensors, and moving parts will go a long way towards the successfulcompletion of your very own mobile robot that does real work.289This page intentionally left blank.IndexNote: Figures and tables are indicated by an italic f and t, respectively.AAaroflex, Inc., xviiiabsolute encoders, 46faccelerometers, 132Ackerman, Rudolph, 190Ackerman steering layout, xii, 152, 179f, 190actuatorscable-driven joints, 203, 205count, 67–68, 192direct-drive rotary actuators in leg movement, 203, 205, 206flinear actuators in leg movement, 202–203, 205fand mobility system complexity, 235motor linear, 41–43in rocker bogie suspension systems, 154–155rotary, 66f–68and steering, 192–194stepper-motor based linear, 42f–43addendum circle, 87AeroMet Corporation, xxviiiair-bearing stages, 13all-terrain cycles (ATCs), 137, 197Alvis Stalwart, 152amplifiers.
See motor driversanalog-to-digital converters (ADCs), 60Andros (Remotec), 155Angle, Colin, xiiiangular displacement transducers (ATDs), 55–57, 56farm geometries, 245–249articulated steering, 167Asea Brown Boveri (ABB), 260automatic guided vehicles (AGVs), 192–193autonomous, term defined, xiiiautonomous manipulators, 241axis stages, in motion control systems, 3Bbacklash, 88Ballistic Particle Manufacturing (BPM), xvi, xxvii–xxix,xxviii(f)ballscrew drive, 12fballscrew slide mechanism, 6–7fBayside Controls, Inc., 104bellows couplings, 14f–15beltsabout, 72–73flat belts, 73, 74fO-ring belts, 73, 74ftiming belts, 75f–76fV-belts, 73–74f, 76–77Bendix-Weiss joints, 116bevel gears, 89, 102, 103fBradley Fighting Vehicle (U.S.
Army), 167bumper geometriesabout, 280–2823D motion detection, 287–288fhorizontal loose footed leaf spring, 285–286fsimple bumper suspension devices, 282, 283fsliding front pivot, 286–287ftension spring layout, 284fthree link planar, 283f–284torsion swing arm, 284–285fbutton switch, 266, 267fBv206 four-tracked vehicle (Hagglund), 166, 184Ccable-driven joints, 203, 205291Copyright © 2003 by The McGraw-Hill Companies, Inc. Click here for Terms of Use.292IndexCAM-LEM, Inc., xxiiicamming, electronic, 11Carnegie Mellon University, xxxcartesian arm geometry, 246f–247center of gravity (cg) shifting, 131–134, 132f, 133fcg.
See center of gravity (cg) shiftingchain drivesladder, 80frack and pinion, 82froller, 80–82f, 81fsilent (timing), 82–83fchasms. See crevasse negotiationchassis elevation, 132, 134fCincinnati Milacron, 260circular interpolation, 10circular pitch, 87clearance, 87closed-loop motion control systems (servosystems), 5–9, 5f,6f, 7f, 8f, 18cluster gears, 86fcommutation, 26–28f, 27f, 30, 34–35computer-aided design (CAD), xiv, xvicomputer-aided motion control emulation, 10–11cone clutches, 122fcone drives, 84fconstant-velocity couplings, 115f–116fcontact ratio, 87contouring, 10controlled differential drives, 93–95f, 94fcontrol structures, xiiicostsand actuator count, 68and gearhead installation, 104–105couplersbellows couplings, 14f–15Bendix-Weiss joints, 116constant-velocity couplings, 115f–116fcylindrical splines, 116f–119f, 117f, 118fface splines, 120fflexible shaft couplings, 14fhelical couplings, 14f–15Hooke’s joints, 114fof parallel shafts, 115fCrawler Transporter (NASA), 165crevasse negotiation, 163–164, 166, 234Cubital America Inc., xxcylindrical arm geometry, 247fcylindrical splines, 116f–119f, 117f, 118fDdark fringe, 58DCDT.
See linear variable differential transformers(LVDTs)dead-reckoning error, 196debugging, and actuator count, 67–68dedendum circle, 87degrees-of-freedom (DOF)in manipulator arm geometry, 241–242, 245degrees-of-freedom (DOF)in manipulator wrist geometry, 250–251fin walker mobility systems, 203–208, 204f, 205f, 206f,207fdepth, in gears, 87derivative control feedback, 9design tools, xivdiametrical pitch (P), 87differential, 139–140fDirected-Light Fabrication (DLF), xvi, xxix(f)–xxxDirect-Metal Fusing, xxixdirect power transfer devicescouplersBendix-Weiss joints, 116direct power transfer devicescouplers, 14f–15, 109–113f, 110f, 111f, 112fbellows couplings, 14f–15constant-velocity couplings, 115f–116fcylindrical splines, 116f–119f, 117f, 118fface splines, 120fflexible shaft couplings, 14fhelical couplings, 14f–15Hooke’s joints, 114fof parallel shafts, 115ftorque limiters, 121–125f, 122f, 123f, 124fDirect-Shell Production Casting (DSPC), xvi, xxvi(f)–xxviidrive/steer modules, 195f–197fdrop on demand inkjet plotting, xx, xxviii(f)DTM Corporation, xxidynamic stability, 201–202EE-chains, 243felectric motors.
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