Hammer Drill Tool Holder Restriction for Stable Mode Switching
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Solution Overview
Problem
Existing hammer drills suffer from instability in the retreat restriction position of the tool holder due to the cantilevered eccentric pin structure, leading to potential unexpected striking motions when high pushing forces are applied.
Innovation Solution
A hammer drill design featuring a cylindrical tool holder with a mode switching member and a restricting member that includes multiple symmetrical restricting portions to stabilize the retreat position, supported by a cam mechanism and biasing member, ensuring balanced operation even under increased forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a cantilever eccentric pin structure is used to restrict tool holder retreat, then the device complexity is reduced, but the reliability deteriorates due to deformation and tilting under increased pushing forces
Solution Approach 1:
The single eccentric pin is segmented into multiple pins (first eccentric pin and second eccentric pin) arranged symmetrically on opposite sides of the tool holder. This segmentation distributes the pushing force across multiple support points, preventing deformation and tilting while maintaining structural simplicity.
Solution Approach 2:
The patent uses symmetric arrangement of eccentric pins rather than asymmetric single-pin design. The first and second eccentric pins are positioned symmetrically relative to the tool holder's strike axis, creating balanced force distribution that eliminates the tilting problem inherent in cantilevered asymmetric structures.
2Ease of operation
If the tool holder is allowed to retreat freely for mode switching, then the ease of operation is improved, but the reliability deteriorates due to unexpected striking motions caused by unstable retreat restriction
Solution Approach 1:
The mode switching lever is designed to automatically move the mode switching member to the retreated position (activating the rotation conversion portion) before the user applies significant pushing force. This preliminary positioning ensures that when drilling mode is selected, the tool holder is already in the correct position for hammer drilling operation, preventing unexpected striking motions.
Solution Approach 2:
The system provides mechanical feedback through the engagement of the mode switching member with the first and second eccentric pins. When the tool holder retreats, the pins engage with the lever to maintain the retreated position. When pushing force is applied, the pins disengage to allow return to the advance position, creating automatic position feedback that ensures reliable mode switching.
Data Source
AI summary
A hammer drill includes a motor, a cylindrical tool holder, an intermediate shaft, a rotation conversion portion, a mode switching member, a restricting member, and an operation member. A first switch state of the restricting member by the operation member causes a first operation mode in which rotation of the tool holder and a striking motion of a striking portion allowed to be performed simultaneously in conjunction with retreat of the tool holder. A second switch state of the restricting member by the operation member causes a second operation mode in which the retreat of the tool holder from the advance position is restricted and the tool holder is allowed to be rotated only. The restricting member is provided with a plurality of restricting portions that contact the mode switching member to restrict the retreat of the mode switching member.