| 76 | | }}} |
| 77 | | |
| 78 | | |
| 79 | | |
| 80 | | == !TorqueSwitch™ == |
| 81 | | Barrett Technology’s patented !TorqueSwitch™ mechanism affords the !BarrettHand™ unparalleled weight reduction without sacrificing dexterity or functionality by serving as a “smart” coupling of two finger joints to one motor. The mechanism’s operation is similar to that of a simple screw fastener. Theoretically, the torque with which one tightens a uniform screw should be equal to that which is required to subsequently loosen it (neglecting inertia and provided all materials deformations remain elastic). This principle holds true for the !TorqueSwitch™ mechanism. |
| 82 | | |
| 83 | | The !TorqueSwitch™ consists of a threaded shaft; a pair of Belleville spring washers and a spur gear with a threaded bore, shown in Figure 29. |
| 84 | | |
| 85 | | {{{ |
| 86 | | #!div class="center" align="center" |
| 87 | | [[Image(htdocs:bhand/280/figure29.png)]] |
| 88 | | |
| 89 | | '''Figure 29 - Barrett's Patented !TorqueSwitch™ Mechanism''' |
| 90 | | }}} |
| 91 | | |
| 92 | | |
| 93 | | The following description follows the progression of Figure 30. When the clutch is engaged, both worm gear drives and their corresponding finger links are coupled to the geared servo-motor pinion. In this state, the ratios of motor position to joint position for the 1st and 2nd finger joints are 93.75:1 and 125:1, respectively. |
| 94 | | |
| 95 | | When a finger opens against its motion stop, the threaded spur gear is tightened against the Belleville spring washers with a known motor torque; thereby setting the threshold torque for disengaging the spur gear. If the inner finger link, while closing, contacts a target object of sufficient stiffness to increase the torque in the gear train above the threshold torque, the clutch will disengage from the Belleville spring washers. |
| 96 | | |
| 97 | | When the clutch is disengaged, the threaded spur gear “free-wheels” on the threaded shaft, allowing the motor pinion to turn without inducing motion in the inner link. Instead, only the smaller spur gear, solidly fixed to its shaft, is driven. This fixed spur gear actuates the worm gear drive for the fingertip. Thus, when the clutch is disengaged, the inner finger link remains motionless while the fingertip continues to move allowing the fingers to form-fit around any shape. |
| 98 | | |
| 99 | | {{{ |
| 100 | | #!div class="center" align="center" |
| 101 | | [[Image(htdocs:bhand/280/figure30.png)]] |
| 102 | | |
| 103 | | '''Figure 30 - !TorqueSwitch™ Operation''' |
| 104 | | }}} |
| 105 | | |
| 106 | | The force required to cause the !TorqueSwitch™ to disengage can be set using the properties, IVEL, IOFF, IHIT, and OT. Barrett Technology recommends that users should not change IVEL, IOFF, and IHIT from their default values. The following Breakaway force Curve can be repeated by using OT with the default values. |
| 107 | | |
| 108 | | {{{ |
| 109 | | #!div class="center" align="center" |
| 110 | | [[Image(htdocs:bhand/280/figure31.png)]] |
| 111 | | |
| 112 | | '''Figure 31 - Breakaway Force Curve''' |
| 113 | | }}} |
| 114 | | |
| 115 | | To control how much force is applied to an object being grasped without sensor feedback such as finger-tip torque sensors (strain gauges) or tactile sensors, the MT property must be used. Please see this graph to understand how MT and finger torque are related: |
| 116 | | http://web.barrett.com/support/BarrettHand_Documentation/MotorTorque280.png |
| 117 | | |
| 118 | | |
| 119 | | {{{#!comment |
| 120 | | These commands use the Velocity Control Law with the properties MCV and MOV. To determine the amount of desired force at the fingertip use Figure 32 to select proper velocities. |
| 121 | | |
| 122 | | {{{ |
| 123 | | #!div class="center" align="center" |
| 124 | | [[Image(htdocs:bhand/280/figure32.png)]] |
| 125 | | |
| 126 | | '''Figure 32 – Stalled FingerTip Force Vs. Commanded Velocity (measured before breakaway).''' |
| 127 | | }}} |
| 128 | | |
