Screw Terminal Torque Coordination for Automation
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Solution Overview
Problem
Existing electrical devices with screw terminals face challenges in preventing screw twisting due to vibrations, ensuring accurate alignment for secure connection, and accommodating conductors of maximum permissible diameter without damaging threads, especially when using motorized screwdrivers.
Innovation Solution
The electrical device features a shaft and screw head coordination allowing minimum torque in a first rotation angle range and maximum torque in a second, achieved through a clearance fit and press fit combination, enabling precise alignment and automation of screwdriver operation, with a curved and flat lateral surface design to prevent mechanical damage and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the threaded shaft engages with the internal thread over a certain depth to prevent thread damage, then thread protection is improved, but the clamp opening becomes smaller and cannot accommodate conductors with maximum permissible diameter
Solution Approach 1:
The screw is pre-positioned in the shaft at a specific depth before the electrical device is delivered. This preliminary positioning ensures that the threaded shaft engages with the internal thread at an optimal depth that prevents thread damage while maintaining sufficient clamp opening for maximum conductor diameter. The pre-positioning eliminates the need to adjust screw depth later, resolving the contradiction between thread protection and conductor accommodation.
2Adaptability or versatility
If the screw is loosened to allow insertion of thick electrical conductors, then conductor accommodation is improved, but the threaded shaft is no longer in engagement with the internal thread requiring realignment
Solution Approach 1:
The screw is pre-positioned and fixed in the shaft during assembly, establishing precise thread engagement before the device is delivered. This preliminary action ensures that when thick conductors need to be inserted, the screw maintains its positioned state and does not require loosening or realignment, thus preserving both conductor accommodation capability and thread alignment precision.
3Reliability
If the screw is tightened to ensure thread engagement, then thread protection is improved, but the clamp opening becomes too small for maximum diameter conductors
Solution Approach 1:
The screw is pre-positioned at the optimal engagement depth during assembly, establishing the correct balance between thread engagement and clamp opening size before the device is delivered. This preliminary positioning eliminates the need to over-tighten the screw later, ensuring both reliable thread engagement and sufficient clamp opening for maximum diameter conductors can coexist.
4Productivity
If automatic screwdrivers are used for full automation, then productivity is improved, but precise alignment of the screwdriver opening with the housing is required
Solution Approach 1:
The screw head is designed with an asymmetric geometry featuring a curved lateral surface in the area of maximum screw head diameter and a flat lateral surface in the area of reduced screw head diameter. This asymmetric design, combined with the pre-positioned screw in the shaft, ensures that the screwdriver opening aligns precisely with the housing in a specific angular position. The asymmetric shape provides a unique orientation that facilitates accurate alignment for automatic screwdrivers, enabling full automation while maintaining the required manufacturing precision.
Data Source
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AI summary
The subject matter of the invention is an electrical apparatus (1) with a screw terminal (3) for connecting electrical conductors, comprising a housing (5) with a shaft (7), in which a screw (9) with a screwdriver opening (11) is provided, which screw is surrounded radially by the shaft (7) and can be rotated in a targeted manner only via the screwdriver opening (11) thereof, wherein the screw head (15) and the shaft (7) are matched to one another in such a way that, during a rotation of the screw (9), a minimum torque is passed through in a first rotary angle range and a maximum torque is passed through in a second rotary angle range, wherein the screw head (15) has a maximum screw head diameter (D1) and a screw head diameter (D2) which is reduced in comparison therewith, wherein the shaft (7) contains a first shaft diameter (DS1) which corresponds to the maximum screw head diameter (D1), and a smaller second shaft diameter (DS2), wherein the lateral surface of the screw head (15) is curved in the region of the maximum screw head diameter (D1) and is planar in the region of the reduced screw head diameter (D2).