Pretensioned Workpiece Holder for Load-Induced Alignment Control
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Solution Overview
Problem
The weight force of a workpiece causes deformation in the workpiece holder device, leading to machining inaccuracies due to deviations from the desired position.
Innovation Solution
A workpiece holder device with a support part and a holder part, featuring at least one pretensioning device that applies static or quasistatic pretension to counteract deformation, reducing the modulus of elasticity and minimizing position deviations under load.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the holder supports the workpiece without pretension, then the holder can accommodate the workpiece easily, but the weight force of the workpiece causes deformation and position deviations
Solution Approach 1:
The pretensioning device applies a preliminary force to the holder structure before the workpiece is loaded. This preliminary action creates a pre-compression or pre-tension state in the holder that counteracts the deformation caused by the workpiece weight during machining, thereby maintaining position accuracy without requiring complex active compensation systems
Solution Approach 2:
The invention changes the mechanical parameter of the holder by introducing pretension, which alters the stress state and stiffness characteristics of the holder structure. This parameter change allows the holder to resist deformation from workpiece weight while maintaining structural simplicity
2Speed
If piezo actuators are used to compensate for vibrations, then rapid control is achieved, but the travel and elastic deformation capability are limited
Solution Approach 1:
Instead of using piezo actuators for position correction during machining, the invention applies pretension before loading the workpiece. This preliminary action establishes a stable mechanical baseline that prevents the need for large-scale active compensation, allowing the system to maintain both stability and sufficient travel range for the holder mechanism
3Manufacturing precision
If the holder structure is made rigid to prevent deformation, then position accuracy is maintained, but the holder cannot accommodate varying workpiece weights effectively
Solution Approach 1:
The pretensioning device is configured to apply a preliminary force that creates a pre-loaded state in the holder structure. This preliminary action allows the holder to adapt to different workpiece weights while maintaining alignment accuracy, as the pretension provides a stable mechanical baseline that compensates for varying loads
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 pretensioning device effectively maintains the desired alignment of the holder part by reducing elastic deformation caused by the workpiece's weight force, minimizing machining inaccuracies and maintaining consistent pretension during operation.
Implementation Method 1
the weight force of the workpiece can cause a deformation
Implementation Method 2
The pretensioning device can pretension at least one part of the support part and/or of the holder part
Data Source
AI summary
A workpiece holder device for a machine tool has a holder, which has a support part and a holder part. The support part supports the holder on a support device, preferably so that the holder can rotate about an axis of rotation. The holder part is set up to hold a workpiece directly or indirectly. To avoid, or at least minimize deviations from a desired alignment of the holder part based on elastic deformation of the holder due to the weight force of the workpiece, the holder has at least one mechanical or hydraulic pretensioning device arranged on or in it. The pretensioning device can be used to pretension the material of the holder, so that the pretensioning device applies a tensile stress or a compressive stress to at least one part of the holder. This can counteract a deviation of position due to an elastic deformation of the holder.