Convergent-Taper Collet Assembly for Stable Clamping of Short Workpieces
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Solution Overview
Problem
Existing clamping units for machine tools, such as collet chucks, struggle to firmly grip workpieces with both significant and reduced longitudinal extensions, leading to ejection of pieces with smaller dimensions due to the clamping elements' rotational movement.
Innovation Solution
A clamping unit design featuring a collet with a convergent outer surface and a seat with a convergent inner surface, combined with a pusher mechanism, ensures that the workpiece is positioned within the clamping cavity, preventing rotational ejection and allowing firm clamping of pieces with varying dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a collet with divergent outer surface and seat with divergent inner surface is used, then pieces with significant longitudinal extensions can be clamped firmly, but pieces with reduced longitudinal extensions cannot be clamped firmly due to rotational ejection
Solution Approach 1:
The patent inverts the traditional divergent taper geometry to use convergent tapers instead. The collet head portion has an outer surface tapered in a convergent manner towards the front opening, and the seat front portion has an inner surface tapered in a convergent manner towards the front opening. This geometric inversion changes the mechanical behavior: when the collet is pulled rearward, the convergent surfaces cause clamping elements to move radially inward without rotating, preventing ejection of short pieces while maintaining clamping effectiveness for long pieces.
2Force
If the clamping elements are allowed to rotate to grip the workpiece, then clamping force is generated, but the workpiece is ejected due to rotational movement
Solution Approach 1:
By inverting the taper geometry from divergent to convergent, the patent eliminates the rotational component of clamping element movement. The convergent surfaces guide the clamping elements to move purely radially inward when the collet is actuated, generating clamping force without the rotational motion that causes ejection. This resolves the contradiction between generating clamping force and maintaining workpiece stability.
3Ease of operation
If the collet is pulled rearward to activate clamping, then clamping elements move closer to the clamping axis, but this causes rotation and ejection of short pieces
Solution Approach 1:
The patent maintains the simple rearward pull activation mechanism but changes the geometric response. The convergent taper surfaces ensure that rearward movement of the collet translates purely into radial inward movement of clamping elements, eliminating rotation. This preserves ease of operation while preventing workpiece ejection and improving 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 clamping unit effectively secures workpieces with significant and reduced longitudinal extensions by ensuring they are fully contained within the clamping cavity, preventing rotational ejection and enhancing stability during machining.
Implementation Method 1
the head portion of the collet defines an outer surface tapered in a convergent manner towards the front opening of the collet holder seat, and the front portion of the collet holder seat has an inner surface also tapered in a convergent manner towards the front opening. The inner surface of the front portion of the seat is operatively associated with the outer surface of the collet so as to control the position of the clamping elements of the collet with respect to the clamping axis as a function of the position of the collet in the seat
Data Source
Figure 1a~1b
Figure 2
Figure 3a~3b
AI summary
The present invention concerns a clamping unit (1) configured to clamp a workpiece (P) around a clamping axis (A-A), comprising: - a collet holder (2) defining a seat (20) which extends along the clamping axis (A-A) between a front portion (20a) provided with a front opening (20c) and a rear portion (20b), - a collet (3) slidably mounted in the seat (20) of the collet holder (2), extending between a tail portion (30a) and a head portion (30b), and comprising: - clamping elements (30) arranged around the clamping axis (A-A) and separated along a circumferential direction (C-C) so as to be mutually movable away from/closer to the clamping axis (A-A) to switch the clamping unit (1) between a clamping and opening configuration, - elastic elements (33) arranged around the clamping axis (A-A) in interposition between the clamping elements (30) along the circumferential direction, - a pusher (5) slidably mounted in the seat (20) along the clamping axis (A-A) and configured to push the collet (3) towards the front opening (20c) of the seat (20) and switch the clamping unit (1) from the opening configuration to the clamping configuration or keep it in the clamping configuration. A feature of the present invention is that the head portion of the collet (3) has an outer surface (30c) tapered in a convergent manner towards the front opening (20c), and that the front portion (20a) of the seat (20) has an inner surface (20d) also tapered in a convergent manner towards the front opening (20c) which, in use, controls the position of the clamping elements (30) with respect to the clamping axis (A-A) as a function of the position of the collet (3) in the seat (20).