| | 2 | |
| | 3 | == !Finger Drivetrain and TorqueSwitch™ == |
| | 4 | |
| | 5 | It is easiest to understand Barrett's patented TorqueSwitch™ mechanism by first understanding the operation of the BarrettHand finger assembly. The image below shows a single finger without the rest of the Hand, including all critical drive elements. |
| | 6 | |
| | 7 | {{{ |
| | 8 | #!div class="center" align="center" |
| | 9 | [[Image(htdocs:bhand/282/OverallFinger.PNG)]] |
| | 10 | |
| | 11 | '''Single BarrettHand Finger Assembly''' |
| | 12 | }}} |
| | 13 | |
| | 14 | |
| | 15 | This second image is a close-up of the drive elements in the finger. During normal operation, the motor shaft/pinion (gray) drives both the distal (yellow) and proximal (blue) gears, which transmit power through their respective worms (red and green) and into two worm gears (orange and purple). The proximal worm gear (purple) is tied directly to the proximal link with six screws, whereas the distal gear (orange) connects to the distal link via mechanical cable. The net result is a motion ratio of 93.75:1 for the motor shaft to proximal joint position and a 125:1 reduction for the motor shaft to distal joint position. |
| | 16 | |
| | 17 | {{{ |
| | 18 | #!div class="center" align="center" |
| | 19 | [[Image(htdocs:bhand/282/FingerDriveElements.PNG)]] |
| | 20 | |
| | 21 | '''BarrettHand Finger Drive Elements''' |
| | 22 | }}} |
| | 23 | |
| | 24 | The connection between the proximal worm (green), the belleville washers (pink) and the proximal gear (blue) is the critical part of this assembly that makes the TorqueSwitch™ work. The proximal gear is internally threaded, and rides on threads cut into the worm shaft, while the belleville washers are compressed between the side of the gear and a shoulder on the shaft. |
| | 25 | |
| | 26 | When the proximal link contacts a stiff surface, the resultant resistance in the worm causes the gear to back off the washers by twisting back up the threaded worm shaft. The resistance must be sufficiently large to overcome the friction between the gear and shaft that comes from the belleville washer compression. The sequence of images below shows this process. |
| | 27 | {{{ |
| | 28 | #!div class="center" align="center" |
| | 29 | [[Image(htdocs:bhand/282/WormSpinning.png)]] |
| | 30 | |
| | 31 | '''The worm and proximal gear rotate together at first.''' |
| | 32 | }}} |
| | 33 | |
| | 34 | |
| | 35 | {{{ |
| | 36 | #!div class="center" align="center" |
| | 37 | [[Image(htdocs:bhand/282/Breakaway.png)]] |
| | 38 | |
| | 39 | '''When the proximal link encounters adequate resistance, the proximal gear backs off the belleville washers and the link stops moving.''' |
| | 40 | }}} |
| | 41 | |
| | 42 | |
| | 43 | {{{ |
| | 44 | #!div class="center" align="center" |
| | 45 | [[Image(htdocs:bhand/282/BrokenAway.png)]] |
| | 46 | |
| | 47 | '''The proximal gear then moves up the worm shaft, leaving the proximal link immobile but allowing the distal link to continue to move.''' |
| | 48 | |
| | 49 | '''Enough threaded shaft is provided such that the distal link will close fully before the proximal gear runs out of space.''' |
| | 50 | |
| | 51 | '''The distal link continues until it closes around the object.''' |
| | 52 | }}} |
| | 53 | |
| | 54 | The TorqueSwitch™ is reset by opening the finger fully. This drives the proximal gear against the belleville washers when the proximal link contacts its joint stop, preloading the system appropriately. The amount of prelod can be altered by changing the "OT" parameter in the Puck driving that finger. |
| | 55 | |
| | 56 | Finally, it is important to note the two magnets and their associated magnetic encoders at the ends of the motor shaft and worm shaft. These two encoders allow the Puck to determine the position of both joints in the finger (the proximal link via the worm encoder and the distal link via the motor encoder). |
