Clamping Device Backlash Elimination via Ball Screw Drive
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Solution Overview
Problem
Existing clamping devices for machine tools suffer from slippage and backlash in the movement converter, leading to inaccurate positioning of clamping jaws and limited control over clamping force, making them unsuitable for precise machine tool operation.
Innovation Solution
A clamping device with a stationary electronic rotary encoder and a prestressed ball screw drive, combined with a force accumulator using helical compression springs, ensures backlash-free and slip-free adjustments, allowing precise control and monitoring of the machine tool.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If planetary roller spindles are used in the movement converter, then the clamping device can convert rotational movements into axial adjustments, but slippage occurs due to inclined thread position and pitch angle, leading to inaccurate positioning
Solution Approach 1:
The patent replaces the planetary roller spindle mechanism with a ball screw drive mechanism. The ball screw drive converts rotational movement of the drive motor into precise axial movement of the drawbar through a ball nut and ball screw combination, eliminating the slippage inherent in planetary roller spindles. This substitution provides backlash-free, precise positioning while maintaining the function of converting rotational to linear motion.
Solution Approach 2:
The patent changes the transmission mechanism parameters by using a ball screw drive with specific lead and pitch characteristics. The ball screw drive allows for precise control of the drawbar's axial position through controlled rotation, with the ball nut translating rotational displacement into linear displacement without slippage. This parameter change enables accurate positioning feedback through the rotary encoder.
2Adaptability or versatility
If direction of rotation changes between clamping and unclamping, then the clamping device can perform bidirectional operations, but dead movement occurs which prevents axial position determination
Solution Approach 1:
The ball screw drive mechanism eliminates dead movement by providing a direct, reversible transmission path. When the drive motor reverses rotation direction, the ball nut immediately follows with corresponding axial movement in the opposite direction, with no lost motion. This allows continuous, precise positioning feedback through the rotary encoder during both clamping and unclamping operations.
Solution Approach 2:
The ball screw drive maintains continuous transmission of motion in both directions without interruption or dead zones. The ball nut remains engaged with the ball screw throughout the full range of motion, ensuring that every degree of rotor shaft rotation is immediately and accurately reflected in the axial position of the drawbar, enabling continuous position determination during bidirectional operations.
3Power
If plate springs are used in the energy storage device, then the device can store elastic energy, but the small spring deflection is insufficient for satisfactory machine tool control
Solution Approach 1:
The patent changes the spring type from plate springs to helical compression springs. Helical compression springs provide significantly larger deflection ranges while maintaining the required clamping force. This allows the energy accumulator to accommodate the full travel range of the ball screw drive, enabling the drawbar to move from fully retracted to fully extended positions while the springs remain within their elastic range, thus providing satisfactory machine tool control.
Solution Approach 2:
The energy accumulator uses multiple helical compression springs arranged in parallel, creating a composite spring system. This configuration increases both the total clamping force capacity and the overall deflection range, as the springs work together to provide both high force and large travel capability, overcoming the limitations of single plate springs.
4Force
If disc springs are used for clamping force adjustment, then the energy storage device can maintain clamping force, but the adjustment range is insufficient for changing operating conditions
Solution Approach 1:
The patent changes from disc springs to helical compression springs, which offer a much broader adjustment range. The helical compression springs can be compressed over a large range of distances, allowing the clamping force to be adjusted from maximum to minimum values. This enables adaptation to various operating conditions, including different workpiece sizes, material types, and machining operations, while maintaining reliable force storage 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
The solution provides precise control and monitoring of the machine tool by eliminating slippage and backlash, enabling accurate determination of the clamping force and position, and allowing adaptable clamping force adjustments, ensuring reliable and precise operation.
Implementation Method 1
drive the adjustment element of the movement converter directly to the actuating element via a prestressed ball screw drive
Implementation Method 2
force accumulator using helical compression springs
Implementation Method 3
force accumulator with a large number of helical compression springs distributed evenly over the circumference
Implementation Method 4
stationary electronic rotary encoder assigned to one of the components of the clamping device involved in the power transmission to determine the axial adjustment movements of the drawbar
Data Source
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AI summary
A clamping device (1) for machine tools (2), equipped with a power chuck (5) and comprising a switchable electric drive motor (11) for initiating clamping movements, a motion converter (31) for converting the adjustment movements into the axial movements of a drawbar (7), and a power storage device (41), is designed as a backlash-free and slip-free functional unit. To determine the axial adjustment movements of the drawbar (7) during clamping and unclamping of a workpiece (10), a stationary electronic rotary encoder (101) is assigned to one of the components (53; 54) involved in the power transmission. This design makes it possible to design the clamping device (1) as inherently rigid, exhibiting neither backlash nor slippage, so that both the axial adjustment movements of the drawbar (7) and thus the respective operating positions of the clamping jaws (6) of the power chuck (5) can be used without restriction.The control of the machine tool (2) can thus be accomplished easily and very precisely, without having to accept any inaccuracies.