Power Tool Spindle Clamp Mechanism for Rapid Stop Retention
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Solution Overview
Problem
The rapid stopping of a power tool spindle can cause the angular inertia of the accessory and nut to dislodge, posing a safety risk as they may fly off, due to insufficient retention mechanisms in existing clamp systems.
Innovation Solution
A clamp mechanism featuring an inner spindle with a spring member and a shoulder bolt system that applies axial forces to secure the accessory, combined with a depressor mechanism and actuation system to enhance friction and rotational locking, preventing the accessory from coming loose during quick spindle stops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional clamp mechanism with nut and threaded spindle is used, then the accessory can be mounted and removed, but the accessory may dislodge during rapid spindle stopping due to angular inertia
Solution Approach 1:
The spindle is divided into two functional parts: an outer spindle that rotates with the motor and an inner spindle that remains stationary during rotation. The inner spindle carries the clamping mechanism while the outer spindle provides rotational motion. This segmentation allows the clamping force to be applied independently from the rotating accessory, preventing dislodgment during rapid stopping.
Solution Approach 2:
The spring member continuously applies a preliminary clamping force on the accessory through the inner spindle before any disturbance occurs. This preliminary action ensures that the accessory is pre-loaded against the outer spindle, creating sufficient friction to resist dislodgment during rapid deceleration events.
2Speed
If the spindle is braked quickly to stop the motor, then the tool responds faster, but the angular inertia causes the accessory to fly off
Solution Approach 1:
The spring member continuously applies a preliminary clamping force on the accessory through the inner spindle before any disturbance occurs. This preliminary action ensures that the accessory is pre-loaded against the outer spindle, creating sufficient friction to resist dislodgment during rapid deceleration events.
Solution Approach 2:
The inner spindle acts as an intermediary element between the clamping mechanism and the rotating outer spindle. It transfers the clamping force from the stationary clamping mechanism to the rotating accessory without itself rotating, allowing the accessory to remain securely clamped even during rapid spindle stopping.
3Reliability
If friction between the accessory and spindle is increased to prevent dislodgment, then retention improves, but the actuation mechanism requires more force
Solution Approach 1:
The depressor mechanism provides dynamic control of the clamping force. During actuation, the depressor temporarily overcomes the spring force to release or clamp the accessory. Once actuated, the spring maintains the clamping force automatically without requiring continuous application of high force by the user.
Solution Approach 2:
The spring member provides a continuous partial clamping force that is sufficient for normal operation. The depressor mechanism only needs to apply excessive force temporarily during actuation to overcome this spring force and change the clamping state, rather than requiring the user to continuously apply high force.
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 mechanism significantly increases frictional force between the accessory and spindle, effectively preventing the accessory and nut from dislodging during braking, thereby enhancing safety by maintaining secure attachment during sudden stops.
Implementation Method 1
the friction between the tension member and the depressor has to be reduced by roller bearings
Implementation Method 2
a spring member arranged to apply a biasing force on the inner spindle in a first direction with respect to the outer spindle
Implementation Method 3
an actuation mechanism arranged to apply force on the second end of the depressor to axially move the first end of the depressor into selective engagement with the second end of the drive spindle
Implementation Method 4
the inner spindle includes a lower portion extending out of the end portion of the outer spindle and having a threaded portion arranged to be received through an opening of the working accessory
Data Source
Figure 1
Figure 2
Figure 3~5
AI summary
A power tool is provided including a motor driving a shaft and a drive spindle. The drive spindle includes an outer spindle rotatably driven by the shaft and an inner spindle disposed within the outer spindle. The outer spindle includes an end portion defining an engagement surface for mounting a working accessory, and the inner spindle is axially moveable along a longitudinal axis of the outer spindle but rotationally fixed to the outer spindle. A spring member is arranged to apply a biasing force on the inner spindle in a first direction with respect to the outer spindle. Securing the working accessory on the drive spindle against the engagement surface of the outer spindle applies an axial force on the inner spindle in a second direction opposite the first direction with respect to the outer spindle.