Ball Screw Robotic Gripper for Direct Force Control
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Solution Overview
Problem
Existing robotic grippers rely on indirect force control schemes that require extra force sensors and are prone to instability due to contact modeling errors, and are often not backdrivable, making them unsafe for interacting with diverse items of varying characteristics.
Innovation Solution
A gripper assembly with a ball screw actuator assembly that provides direct force control by connecting the actuator directly to the ball screw shaft, allowing precise force control without the need for external force measurement, and is mechanically backdrivable, ensuring safe interaction with items of varying characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If indirect force control schemes are used with position control or force plus position control, then the gripper can control finger positions, but extra force sensors are required and the control is prone to instability
Solution Approach 1:
The patent replaces the need for force sensors by substituting the measurement function with a direct mechanical force control mechanism. The direct connection between the actuator and ball screw shaft creates a mechanically backdrivable system where the actuator can be controlled to apply precise forces without requiring separate sensing elements, thereby eliminating the need for extra force sensors while maintaining measurement capability through the mechanical linkage itself.
Solution Approach 2:
The ball screw assembly acts as an intermediary mechanism between the actuator and the finger assemblies. This intermediary component translates actuator motion into controlled finger movement while providing a mechanically backdrivable connection that enables direct force control, serving as a mediator that eliminates the need for separate force sensing while maintaining precise force application capability.
2Reliability
If indirect force control schemes are used, then force can be limited, but the control is prone to instability due to contact modelling errors
Solution Approach 1:
The patent replaces complex contact modeling requirements with a direct mechanical force control system. By creating a mechanically backdrivable connection through the ball screw assembly, the system achieves stable force control without relying on computational contact models, thereby improving reliability by eliminating the source of instability associated with contact modeling errors.
3Object-affected harmful factors
If most grippers are made non-backdrivable, then they provide controlled force, but they become less safe to interact with
Solution Approach 1:
The patent implements a dynamically adjustable force control system through the mechanically backdrivable ball screw assembly. The system can adapt its backdrivability characteristics based on operational requirements, allowing safe interaction during normal operation while maintaining controlled force application. This dynamic capability enables the gripper to be both safe and adaptable to various interaction scenarios.
4Force
If ball screw shaft is subjected to radial forces, then the shaft can bend, but friction between ball screws and shaft increases
Solution Approach 1:
The patent segments the force transmission path by introducing a carriage assembly that separates the radial force bearing function from the ball screw shaft. The carriage assembly absorbs radial forces through its guide rails, while the ball screw shaft maintains its primary function of transmitting axial driving forces, thereby preventing shaft bending and reducing friction losses in the ball screw mechanism.
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
Enables precise direct force control and safe interaction with items of varying characteristics by eliminating the need for external force sensors and reducing friction, while maintaining stability and compliance.
Implementation Method 1
a ball screw assembly comprising a first ball screw nut connected to the first finger assembly and a ball screw shaft comprising a first section upon which the first ball screw nut is movably mounted, the ball screw shaft being rotatable about its longitudinal axis
Implementation Method 2
an actuator directly connected to the ball screw shaft and configured to rotate the ball screw shaft about its longitudinal axis
Implementation Method 3
This configuration isolates the ball screw actuator assembly from any forces applied to the gripper assembly as a result of manipulating an item and transfers them to the first carriage assembly and the one or more guide rails. In particular, it ensures that any radial forces are not brought to bear on the ball screw shaft, which could bend the ball screw shaft and consequently increase the friction between the ball screws and ball screw shaft.
Data Source
Figure 1
Figure 2a
Figure 2b
AI summary
This disclosure relates to a gripper assembly (122) for a robotic manipulator (121). The gripper assembly (122) includes two finger assemblies (132,146) and a ball screw assembly comprising a first ball screw nut (136) connected to the first finger assembly (132) and a ball screw shaft (138) comprising a first section (140) upon which the first ball screw nut (136) is movably mounted. An actuator (154) is directly connected to the ball screw shaft (138) and configured to rotate the ball screw shaft (138) about its longitudinal axis to move the first finger assembly (132) in a direction of the second finger assembly (146) when the ball screw shaft (138) is rotated in one of a clockwise or anticlockwise direction and to move the first finger assembly (132) in a direction away from the second finger assembly (146) when the ball screw shaft (138) is rotated in the other of the clockwise or anticlockwise directions.