Tendon-Driven Serial Robot Actuation Using Planetary Gear Transmission
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Solution Overview
Problem
Tendon-driven joint configurations in serial robots, such as multi-jointed robotic fingers, often result in large stroke and out-of-range errors, constraining the use of smaller actuators and limiting packaging design due to the need for linear actuation near the proximal joint.
Innovation Solution
A transmission system with gear elements, including planetary gear sets or pulley gears, is used to assist in the rotation of the distal joint, allowing for more compact packaging designs and reduced stroke by linking the proximal and distal joints, enabling the use of smaller actuators.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a typical tendon-driven joint configuration is used to actuate a distal joint, then the joint can be actuated, but relatively large stroke and out-of-range errors result
Solution Approach 1:
A transmission mechanism with gear elements is introduced as an intermediary between the actuator and the distal joint. This transmission system includes intermediate gears that transfer and modify the motion from the actuator to the distal joint, enabling precise control of the joint's movement range and reducing unwanted stroke and out-of-range errors.
2Ease of operation
If joint actuators are located near the proximal joint to actuate distal joints, then actuation is achieved, but the range of available actuators is constrained and packaging becomes less compact
Solution Approach 1:
The transmission system is segmented into multiple gear elements (including planetary gear sets and pulley gears) that distribute the actuation function across different components. This segmentation allows the actuator to be positioned near the proximal joint while still effectively controlling the distal joint, improving packaging compactness by utilizing the existing spatial arrangement of the serial robot segments.
3Manufacturing precision
If a transmission system with gear elements is added to reduce stroke, then actuation precision improves and packaging becomes more compact, but device complexity increases
Solution Approach 1:
The transmission system with gear elements serves multiple functions simultaneously: it reduces unwanted stroke, corrects out-of-range errors, enables compact packaging by utilizing existing spatial arrangements, and maintains actuation precision. By designing the transmission to perform these multiple functions, the increase in device complexity is justified by the significant improvements in precision and compactness.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The transmission system effectively reduces unwanted stroke and enables more compact packaging designs in serial robots, allowing for the use of smaller actuators and improving the range of available joint actuators, enhancing the dexterity and efficiency of robotic systems.
Implementation Method 1
the transmission includes a planetary gear set
Implementation Method 2
the gear element may be a pulley gear having an offset center
Data Source
AI summary
A serial robot includes a base, first and second segments, a proximal joint joining the base to the first segment, and a distal joint. The distal joint that joins the segments is serially arranged and distal with respect to the proximal joint. The robot includes first and second actuators. A first tendon extends from the first actuator to the proximal joint and is selectively moveable via the first actuator. A second tendon extends from the second actuator to the distal joint and is selectively moveable via the second actuator. The robot includes a transmission having at least one gear element which assists rotation of the distal joint when an input force is applied to the proximal and/or distal joints by the first and/or second actuators. A robotic hand having the above robot is also disclosed, as is a robotic system having a torso, arm, and the above-described hand.