Cam Mechanism Run-off Securing Device for Power Tools
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Solution Overview
Problem
Existing safety devices for hand-held power tools fail to effectively prevent clamping elements and tools from running off the spindle during braking operations, leading to potential detachment and safety risks due to relative movements caused by mass moments of inertia.
Innovation Solution
A safety device featuring a cam mechanism with a control element that engages partially in a control recess, converting relative movements between the spindle and transmission unit into axial movements to maintain clamping force, thereby preventing the clamping nut and tool from detaching, utilizing a pin-shaped control element and spring elements for secure coupling and prestressing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional safety device without cam mechanism is used, then the structure is simpler, but the clamping force cannot be maintained during braking operations, causing the tool to run off the spindle
Solution Approach 1:
The cam mechanism dynamically adjusts the clamping force during braking operations. The control element moves within the control recess as the spindle decelerates, automatically maintaining adequate clamping force despite the tool's inertia. This dynamic response resolves the contradiction by providing reliable run-off prevention only when needed during braking, rather than requiring continuous complex mechanisms.
Solution Approach 2:
The cam mechanism acts as an intermediary between the spindle rotation and the clamping element. It translates rotational movement into axial movement that maintains clamping force, mediating the conflict between the tool's inertial tendency to runaway and the clamping element's need to maintain grip. This intermediary mechanism provides the necessary reliability without directly complicating the entire device structure.
2Ease of manufacture
If the control element is designed as a pin shape, then the guidance in the control recess is simpler, but the conversion of relative movement requires precise geometric design
Solution Approach 1:
The control recess is designed with specific geometric parameters including a defined opening angle (120° to 150°) and controlled surface roughness (Ra 0.4 to 0.8 µm). These parameter specifications enable the simple pin-shaped control element to function effectively by providing appropriate guidance and movement conversion through the recess's geometric properties, resolving the contradiction between manufacturing simplicity and precision requirements.
3Reliability
If spring elements are added for prestressing, then the clamping force maintenance is improved, but the device complexity increases
Solution Approach 1:
Spring elements are used to apply preliminary prestressing force to the control element, ensuring it maintains contact with the control recess surface and provides continuous clamping force. This preliminary action prevents loss of clamping force during braking operations, improving reliability while adding only minimal structural complexity through the spring components.
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 effectively maintains clamping force during braking operations, preventing the clamping nut and tool from running off the spindle, ensuring axial and rotational safety, and preventing incorrect assembly through coding areas and recesses, thus enhancing the safety and service life of the device.
Implementation Method 1
a cam mechanism (20) having at least one control element (22), wherein the control element (22), by means of an interaction with the control recess (24), is designed to convert a first relative movement between the spindle (16) and a transmission element (26) of the transmission unit (18) into a second relative movement, at least during braking operation
Implementation Method 2
the cam mechanism (20) has at least one spring element which is designed to preload the transmission element (26) relative to the control element (22)
Implementation Method 3
The transmission unit can be detachably secured to the spindle by means of a positive-locking connection and/or a friction-locking connection
Data Source
Figure 1
Figure 2
Figure 3~4
AI summary
The invention is based on a run-off securing device, in particular a hand-held power-tool run-off securing device, for avoiding running-off of a clamping element (12a; 12b; 12c) and/or a tool (14a; 14b; 14c) from a spindle (16a; 16b; 16c), comprising at least one transmission unit (18a; 18b; 18c) and at least one cam mechanism (20a; 20b; 20c), which has at least one control element (22a, 72a; 22b, 72b; 22c, 72c). It is proposed that the cam mechanism (20a; 20b; 20c) has at least one control recess (24a, 74a; 24b, 74a; 24c, 74c), in which the control element (22a, 72a; 22b, 72b; 22c, 72c) at least partially engages.