Handheld Work Apparatus Actuator with Dynamic Force Profile
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Solution Overview
Problem
Handheld work apparatuses with two-handed safety mechanisms require users to continuously resist spring return forces during operation, making them easy to switch on unintentionally and requiring less effort when return springs are weaker.
Innovation Solution
A handheld work apparatus with a transmission element and electrical switching element configuration that requires high actuating forces to switch on the electric drive motor and reduces holding forces after activation, featuring a displacement path with a steeply increasing and then decreasing shift force to ensure secure operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If return springs are made weaker to reduce continuous resistance during operation, then user comfort during working period is improved, but the work apparatus can be switched on very easily with little effort which reduces safety
Solution Approach 1:
The patent applies dynamics by making the resistance force dynamic rather than static. The return spring force varies along the displacement path of the transmission element, being stronger in the first path segment (near rest position) and weaker in the second path segment (near operating range). This dynamic force profile allows high switch-on force requirement while maintaining acceptable holding force during operation.
Solution Approach 2:
The patent changes the parameter of spring force along the displacement path. By configuring the return spring to exert different forces at different positions, the system achieves both high initial resistance for safety and lower continuous resistance for comfort. The spring force parameter is optimized to decrease as the transmission element moves from rest position toward operating range.
2Reliability
If return springs are made stronger to prevent unintentional switching on, then protection against unintentional starting is improved, but the user must continuously resist high spring return forces during operation reducing comfort
Solution Approach 1:
The return spring is configured to provide dynamic resistance that changes with position. During the switching-on phase (first path segment), the spring exerts strong force to prevent unintentional activation. Once switched on (second path segment), the spring force decreases to reduce continuous resistance on the user, thereby resolving the contradiction between safety and comfort.
Solution Approach 2:
The spring force parameter is optimized to vary along the transmission element's displacement path. The system transitions from high force state (for safety) to low force state (for comfort) as the actuating element moves from rest position to operating position, effectively resolving the contradiction between these two opposing requirements.
3Reliability
If a two-handed safety mechanism with multiple actuating elements is used, then protection against unintentional starting is improved, but the device complexity increases
Solution Approach 1:
The patent applies local quality by concentrating the safety function in a specific location (the transmission element's displacement path characteristics) rather than distributing it across multiple actuating elements. The non-linear spring force profile at a single actuating point provides the same safety as multi-element mechanisms without the associated complexity.
Solution Approach 2:
The patent extracts the safety function from the actuating element structure and implements it through the transmission element and spring system instead. This separates the safety mechanism from the actuating mechanism, allowing a single actuating element to provide both operation and safety functions, thereby reducing device complexity while maintaining reliability.
Data Source
AI summary
A handheld work apparatus has a device for starting an electric drive motor via an actuating element which can be displaced in a handle counter to an actuating force and acts on a transmission element. The transmission element is shiftable from a rest position into an operating range, wherein the transmission element actuates a switching element and starts the motor. For shifting from the rest position into an end position, a shift force is applied. The shift force forms at least a portion of the actuating force. To keep the actuating force low after the motor is switched on, the displacement path of the transmission element is divided into a first segment and a second segment which includes the operating range. The shift force to be applied to the transmission element rises on the first segment of the path and, after a maximum, decreases on the second segment.