Hand-Held Power Tool Motion Sensing for Jam Shutdown
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Solution Overview
Problem
Hand-held power tools, such as angle grinders and saws, risk sudden jamming during material processing, leading to uncontrolled movements that can injure users and damage the tool, as existing safety shutdown methods rely on detecting overall tool movement rather than specific tool conditions.
Innovation Solution
A method using sensors to detect linear acceleration and rotational velocity values, adjusting for gravity, integrating and filtering these values to predict the tool's movement, and initiating a safety action if the tool exceeds defined limits, thereby preventing injuries and tool damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If safety shutdown is triggered only when motion variables exceed a threshold, then false shutdowns during normal operation are reduced, but rapid tool movements caused by jamming cannot be detected quickly enough
Solution Approach 1:
The system performs preliminary integration of acceleration data to obtain velocity and position information before a jamming event occurs. By continuously calculating anticipated tool position based on current motion state, the system is prepared to immediately detect when actual position deviates from anticipated position, enabling rapid response without waiting for motion thresholds to be exceeded.
Solution Approach 2:
The patent introduces an intermediary calculation step by integrating acceleration data to derive velocity and position. This intermediary velocity information serves as a bridge between raw acceleration measurements and final safety decisions, allowing the system to detect rapid movements through position deviation rather than relying solely on acceleration thresholds.
2Measurement precision
If motion sensors are positioned close to the tool, then tool movement detection is more accurate, but sensor vulnerability to damage increases
Solution Approach 1:
The system segments the measurement function by placing sensors in the tool housing away from the cutting tool, rather than attaching them directly to the tool. Multiple sensors (acceleration sensors and/or rotation rate sensors) are distributed at different locations within the housing, with each sensor contributing to the overall detection capability while remaining protected from direct exposure to cutting hazards.
Solution Approach 2:
The patent uses the tool housing as an intermediary structure between the sensors and the cutting tool. Sensors are positioned in the housing at a distance from the tool, and the housing itself acts as a protective barrier. The system calculates tool movement by integrating sensor data rather than directly measuring tool position, providing an indirect but protected measurement approach.
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
This method effectively detects rapid tool movements caused by jamming and initiates quick safety actions, such as drive shutdown or active braking, to prevent injuries and ensure tool safety.
Implementation Method 1
at least one sensor device (6), wherein the sensor device (6) is configured to detect at least one linear acceleration value and in particular at least one rotation rate value
Implementation Method 2
subtracting the acceleration due to gravity from the at least one linear acceleration value to obtain at least one adjusted linear acceleration value
Implementation Method 3
integrating the at least one adjusted linear acceleration value to obtain at least one velocity value; integrating the at least one velocity value to obtain at least one distance value
Data Source
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AI summary
The invention relates to a method for operating a hand-held power tool (1) which can be connected to a tool (3). A drive for driving the tool (3), a controller (5), and at least one sensor device (6) are provided. The sensor device (6) is designed to detect at least one linear acceleration value (ax, ay, az) and in particular at least one rotational rate value (ωx, ωy, ωz), and the at least one sensor device (6) is arranged at a distance (D or rD) to a reference point (P) assigned to the power tool (1) or to the tool (3), said distance being greater than or equal to null. The method has the steps of: - detecting at least one linear acceleration value (ax, ay, az) using the at least one sensor device (6); - subtracting the gravitational acceleration from the at least one linear acceleration value (ax, ay, az) in order to form at least one adjusted linear acceleration value (axkorr, aykorr, azkorr); - integrating the at least one adjusted linear acceleration value (axkorr, aykorr, azkorr) in order to form at least one speed value; - integrating the at least one speed value in order to form at least one distance value (sx, sy, sz); - multiplying the at least one speed value by a time constant (τ) in order to form at least one additional distance value: - adding the at least one distance value to the at least one additional distance value in order to form at least one total distance value (sx, sy, sz); - filtering at least one of the linear acceleration values (ax, ay, az, axkorr, aykorr, azkorr) and/or at least one of the speed values; - comparing the at least one total distance value (sx, sy, sz) with a defined threshold; and - initiating a specified action if the at least one total distance value exceeds a defined threshold (GW). The invention additionally relates to a hand-held power tool (1) for carrying out such a method.