Active Contact Force Control with Damped Axial Force Sensing
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Numerically controlled machine tools and robots face challenges in actively controlling forces with real-time accuracy due to variations in workpiece surface geometry, clamping effects, inertia, and limitations of actuators, leading to inadequate operation and undesired oscillations, especially when dealing with tools like polishing, grinding, drilling, milling, or sanding tools.
Innovation Solution
An apparatus with a linear actuator, force sensor, spherical joints, and mechanical dissipative elements (MDE) is used to precisely measure axial force and attenuate non-axial loads and rapid oscillations, while an inertial measurement unit compensates for gravity, ensuring accurate force control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a direct mechanical connection (actuator spindle - force sensor - tool flange) is used, then the structure is simple, but non-axial forces cause measurement errors
Solution Approach 1:
Spherical joints are introduced as intermediary elements between the actuator spindle and force sensor, and between the force sensor and tool flange. These spherical joints act as mediators that decouple non-axial forces (bending and torsional stresses) from the force sensor, allowing only axial forces to be transmitted to the sensor while maintaining structural connectivity.
2Speed
If the control loop operates without mechanical damping, then the system response is fast, but rapid force oscillations occur and can damage the force sensor
Solution Approach 1:
Mechanical dissipative elements (MDE) are pre-installed in the mechanical connection path between the actuator and tool flange. These MDEs provide beforehand cushioning by mechanically attenuating rapid changes in contact force before they reach the force sensor, preventing sensor overload damage and filtering out high-frequency oscillations that would otherwise cause control loop instability.
3Measurement precision
If spherical joints and mechanical dissipative elements are added, then measurement precision and stability improve, but device complexity increases
Solution Approach 1:
The spherical joints serve multiple functions simultaneously: they act as mechanical connectors, force decouplers, and alignment elements. The mechanical dissipative elements provide both vibration attenuation and force smoothing. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in overall device complexity while achieving improved measurement precision and stability.
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 apparatus achieves precise measurement of axial forces and reduces oscillations, enabling higher speed and stability in machining operations, particularly on uneven surfaces, with improved control loop responsiveness and reduced conflict situations.
Implementation Method 1
one or two spherical joints are implemented in the present invention. Their role is to eliminate negative effects of non-axial loads, i.e., bending and torsional stresses, on the installed force sensor in the apparatus according to the present invention
Implementation Method 2
an additional element called - the mechanical dissipative element (MDE) is added. The role of MDE is to mechanically attenuate rapid changes in the contact force measured by the force sensor and, thereby, to prevent system oscillations
Implementation Method 3
The position in the space of the system apparatus - tool is possible to measure from the control system of the multi-axis machine or robotic arm which carries the said system. However, this often affects the autonomous program logic of the multi-axis machine so the extraction of the tool position and orientation in the space is not a simple process for a person skilled in the art.
Data Source
Figure 1
Figure 2~3
AI summary
The present invention discloses the enhanced apparatus for active contact force control. The tool used in the production process is mounted on the upper flange (11) of the apparatus. The apparatus is mounted on the multi-axis machine to obtain spatial motion together with the corresponding tool. The apparatus comprises the housing inside which the linear actuator is installed and connected to the guides (7, 7'). Mechanical connection between the ball screw (4) and the upper flange (11) contains the force sensor (2) and at least one spherical joint (1). The connection between the spherical joint (1) and the upper flange (11) is formed using the mechanical dissipative element made of elastic dissipative elements (12, 14) and the disc plate (13) positioned between them. Mechanical dissipative element is integrated into the upper flange (11). In the preferred embodiment, the apparatus is equipped with the inertial measurement unit (15).