Underactuated Robotic Gripper with Cable-Pulley Actuation
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Solution Overview
Problem
Robotic end-effectors often face design compromises that increase size, weight, or cost when trying to broaden their capabilities, and existing solutions struggle to provide a wide range of grasping forces while maintaining compactness and lightness, making them versatile for interacting with both delicate and heavy objects.
Innovation Solution
A compact, lightweight robotic end-effector design featuring an underactuated system with a series of pulleys and a high-torque driving mechanism, utilizing a non-circular driving cable and sensors for precise force control, allowing for a wide range of grasping forces and independent motion control of fingers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If existing robotic end-effector designs are used to provide a wide range of grasping forces, then the grasping force range is improved, but the size and weight of the device increase
Solution Approach 1:
The end-effector is divided into multiple independent finger assemblies, each with its own underactuated mechanism. This segmentation allows each finger to be lightweight while the collective system provides a wide range of grasping forces through coordinated operation of multiple fingers with different capabilities
Solution Approach 2:
The patent employs underactuated mechanisms where a single motor controls multiple degrees of freedom through cable-pulley systems. This dynamic coupling allows the system to achieve complex grasping motions and force ranges without requiring proportionally more actuators, thus avoiding increased weight
2Force
If existing robotic end-effector designs are used to provide a wide range of grasping forces, then the grasping force range is improved, but the device size increases
Solution Approach 1:
The cable-pulley systems are nested within the finger structures, with pulleys integrated into the finger links and cables routed through the interior of the finger assemblies. This nesting eliminates the need for separate housing spaces, reducing overall end-effector volume while maintaining the complex cable-driven actuation mechanisms
Solution Approach 2:
The underactuated cable-driven mechanisms allow for compact packaging by eliminating the need for multiple motors and gearboxes that would occupy significant space. The flexible cables can be routed through narrow channels within the finger structures, enabling a compact design that achieves wide grasping force ranges
3Weight of moving object
If a compact and lightweight end-effector design is used, then the device size and weight are reduced, but the grasping force range is limited
Solution Approach 1:
The end-effector uses multiple finger assemblies with different actuation characteristics. Each finger is lightweight but the collective system achieves a wide grasping force range by coordinating fingers with different mechanical advantages and cable routing configurations, allowing the lightweight design to compensate for individual finger limitations
Solution Approach 2:
The patent varies key parameters across different finger assemblies, including pulley diameters, cable routing paths, and link dimensions. By optimizing these parameters for each finger while maintaining lightweight construction, the system achieves a wide overall grasping force range without requiring any single finger to be heavy or large
4Adaptability or versatility
If complex actuation mechanisms are added to broaden end-effector capabilities, then the versatility is improved, but the device complexity increases
Solution Approach 1:
The cable-pulley actuation mechanism serves multiple functions simultaneously: it provides actuation forces, transmits motion between joints, and enables both active grasping and passive compliance. This multi-functionality reduces the need for separate mechanisms for each capability, thereby reducing overall device complexity while maintaining versatility
Solution Approach 2:
The underactuated fingers possess inherent compliance and passive motion capabilities that eliminate the need for complex active control mechanisms at each joint. The cable tensioning automatically produces appropriate finger motions and contact forces, reducing control system complexity while maintaining versatile interaction capabilities
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 end-effector achieves a grasping force range significantly higher than human capabilities, enabling interaction with both delicate and heavy objects while maintaining a compact and durable design, which relaxes the design requirements of the robotic arm and overall robot, allowing for increased versatility and dexterity.
Implementation Method 1
the driving cable in contact with the contact sections of the first joint pulley and the second joint pulley such that rotation of the hub alters the tension in the driving cable and induces rotation of at least one of the first or second appendage links
Data Source
AI summary
A compact lightweight robotic end-effector has a large range of possible applied force. The end-effector includes one or more underactuated appendages, where each appendage is driven by a single motor connected to a driving cable wound throughout the appendage. The driving cable may be a flat cable or a cable with another non-circular cross section. The driving cable may be wrapped through a series of pulleys and/or bearings within the appendage to reduce frictional losses. The design of the pulley path may allow a desired mechanical response by the appendage, and the mechanical response may be optimized for a grasping process.