Robotic arms with strap drive trains
In one embodiment of the invention, a robotic arm is provided including a linkage assembly and a strap drive train. The linkage assembly includes first, second, third, and fourth links pivotally coupled in series together at first, second, and third joints to define a parallelogram with an insertion axis. The strap drive train includes first and second sets of straps coupled to the linkage assembly. As the linkage assembly is moved about a pitch axis, the first set of straps ensures the third link maintains the same angle relative to the first link, and the first and second set of straps ensures the fourth link maintains the same angle relative to the second link.
1. A robotic arm comprising:
a linkage assembly including a plurality of links pivotally coupled in series together at one or more joints to slidingly support a tool along an insertion axis, the plurality of links including a first pulley and a second pulley;
at least one strap coupled between the first pulley and the second pulley to drive the linkage assembly; and
a strap tensioning system coupled to the at least one strap, the strap tensioning system to tension the at least one strap;
wherein the strap tensioning system includes
the first pulley having a first pocket;
the second pulley having a second pocket; and
the at least one strap including
a tab coupled to a first end of the at least one strap, the tab to hook into the first pocket of the first pulley to couple the first end of the at least one strap thereto, and
a tensioning block coupled to a second end of the at least one strap, the tensioning block to hook into the second pocket of the second pulley to couple the second end of the at least one strap thereto;
wherein the first pulley further has a first recess in a portion of its circumference joining the first pocket to receive the first end of the at least one strap, a first stop at a front of the first pocket to couple to a front side of the tab, a first side restraining protrusion extending from the first stop to retain the tab in the first pocket, and a first lip at the back of the first pocket to further retain the tab in the first pocket; and
wherein the second pulley further has a second recess in a portion of its circumference joining the second pocket to receive the second end of the at least one strap, a second stop at a front of the second pocket to couple to a front side of the tensioning block, a second side restraining protrusion extending from the second stop to retain the tensioning block in the second pocket, and a second lip at the back of the second pocket to further retain the tensioning block in the second pocket.
2. The robotic arm of claim 1 , wherein the strap tensioning system further includes
a tensioning fastener to tension the at least one strap,
and wherein
the tensioning block has an opening with threads, and
the second pulley further has a cutout and an opening into the second pocket to receive the tensioning fastener and allow the tensioning fastener to mate with the threaded opening in the tensioning block.
3. The robotic arm of claim 2 , wherein the strap tensioning system further includes
a screw-lock helical coil in the threaded opening of the tensioning block to keep the tensioning fastener from rotating and changing tension on the at least one strap.
4. The robotic arm of claim 2 , wherein the strap tensioning system further includes
a locking fastener to keep the tensioning fastener from backing out on its own and reducing the tension on the at least one strap, and
the second pulley further has a threaded opening to receive the locking fastener and couple it against the tensioning fastener.
5. The robotic arm of claim 1 , wherein
the at least one strap is formed of multiple plies of metal generating a spring force to keep the tab locked into the first pocket of the first pulley and the tensioning block locked into the second pocket of the second pulley to avoid complete collapse of the arm if the at least one strap is slackened.