Drill Spindle Axial Force Measurement via Load Cell
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Solution Overview
Problem
Existing drill spindle units face issues with inaccurate feed force measurement due to irregularities in power transmission, leading to misleading motor power output and bulky designs when attempting to measure axial force using multiple bearings and sensing devices.
Innovation Solution
A drill spindle unit with a single axial force sensing device, such as a load cell, integrated between the feed drive sleeve and the housing, which provides a direct and true measurement of axial force applied, unaffected by power transmission irregularities, utilizing needle bearings that do not transfer axial loads, allowing for compact and slim design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple axial force sensing devices are arranged to measure feed force, then measurement precision is improved, but device complexity increases and outer dimensions become bulky
Solution Approach 1:
The patent combines multiple axial force sensing functions into a single load cell that measures the total feed force directly. Instead of using multiple separate sensing devices that require complex signal processing, one load cell integrates the measurement function, simplifying the device structure and signal treatment while maintaining accurate feed force measurement.
2Ease of operation
If motor power output is monitored to control feed force, then ease of operation is improved, but measurement precision deteriorates due to power transmission irregularities
Solution Approach 1:
The patent extracts the feed force measurement function from the motor power monitoring system. Instead of inferring feed force from motor power output (which is affected by power transmission irregularities), the system directly measures feed force using a load cell, eliminating the influence of damaged bearings, gears, and other power transmission components on measurement accuracy.
Solution Approach 2:
The load cell acts as an intermediary device that directly measures the axial feed force between the feed drive mechanism and drill spindle. This intermediary measurement point bypasses the power transmission path, providing accurate feed force data independent of motor power fluctuations or transmission irregularities.
3Device complexity
If needle bearings are used that do not transfer axial loads, then device complexity is reduced and outer dimensions are minimized, but the ability to measure axial force through bearings is lost
Solution Approach 1:
The load cell serves as an intermediary element positioned in the axial force path between the feed drive sleeve and housing. Needle bearings are used to support radial loads without transferring axial loads, while the load cell specifically measures the axial feed force. This separation of functions allows simple bearing arrangement while maintaining accurate axial force measurement capability.
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
This solution provides a precise and direct measurement of axial feed force, unaffected by power transmission malfunctions, simplifying signal treatment and enabling a more compact drill spindle unit with improved accessibility.
Implementation Method 1
an axial force sensing device in the form of a load cell (36) which is arranged to deliver electric signals in response to the axial forces applied on the drill spindle (14)
Data Source
Figure 1~2
AI summary
A drill spindle unit (11) comprises a housing (12), a rotatable and longitudinally displaceable drill spindle (14) provided with axial keyways (20) for cooperation with internal projections (24) of a drill spindle (14) surrounding rotation drive sleeve (21), and a screw thread (26) for cooperation with an internal thread (27) of a drill spindle (14) surrounding feed drive sleeve (22), and bearings (30-32,34) for radial as well as axial support of the drill spindle (14) relative to the housing (12), wherein the radial support bearings (30-32) are arranged to transfer radial forces only, and a thrust bearing (34) is arranged to transfer axial forces between the housing (12) and the drill spindle (14), wherein the thrust bearing (34) is associated with an axial load sensing device (36) by which signals are generated in response to the axial load applied on the drill spindle (14).