Drill Driver Fastener Setting Algorithm Using Current Slope

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Solution Overview

Problem

Existing fastener setting techniques for drill drivers are prone to inaccuracies due to noisy motor current signals, leading to unreliable detection of the desired stopping position.

Innovation Solution

The method involves periodically sampling the current delivered to the electric motor, determining the slope of the current measures using linear regression, and interrupting torque transmission to the output spindle based on the slope and a minimum slope threshold, with secondary checks using motor speed to ensure accurate stopping.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Extent of automation

If motor current behavior is monitored to detect the desired stopping position, then automated fastener setting is achieved, but noise in sensor signals leads to inaccuracies in detection

Engineering Contradiction:

Improveautomated fastener settingVSAvoiddetection accuracy of stopping position

Core Design Contradiction:

Extent of automationVSMeasurement precision

Solution Approach 1:

The current signal is segmented into multiple samples taken at different times during the fastener driving process. By dividing the continuous current signal into discrete time-point measurements, the system can analyze the signal characteristics more effectively and reduce the impact of noise on the detection of the stopping position.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The system performs preliminary sampling of current values at multiple time points before making the final determination of the stopping position. This preliminary action of collecting multiple data points allows the system to process the information and filter out noise before reaching a conclusion, improving detection accuracy.

Inventive Principle:

Principle #10Preliminary action

2Measurement precision

If multiple current samples are processed using linear regression to reduce noise, then measurement precision improves, but device complexity increases

Engineering Contradiction:

Improvedetection accuracy of stopping positionVSAvoidalgorithm complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The system uses linear regression to establish a relationship between time and current values, creating a mathematical model that predicts the expected current behavior. By comparing actual measurements against this model, the system can identify deviations caused by noise and make corrections, improving precision while using a systematic approach to handling the data.

Inventive Principle:

Principle #23Feedback

3Reliability

If the slope counter is adjusted based on slope comparison with threshold, then reliability of stopping position detection is improved, but loss of time increases due to multiple comparisons

Engineering Contradiction:

Improvereliability of stopping position detectionVSAvoidprocessing time for multiple comparisons

Core Design Contradiction:

ReliabilityVSLoss of time

Solution Approach 1:

The slope counter mechanism automatically adjusts itself based on the comparison between the calculated slope and the threshold value. When the slope exceeds the threshold, the counter increments, providing a self-regulating system that accumulates evidence of the stopping condition being met, thereby improving reliability through multiple confirmations.

Inventive Principle:

Principle #25Self-service

Data Source

PatentUS8919456B2Fastener setting algorithm for drill driver

Publication Date: 2014.12.30 BLACK & DECKER CORP

AI summary

An improved technique is presented for detecting when a fastener driven by a drill driver has reaches a desired stopping position. The improved techniques generally includes: sampling periodically current delivered to the electric motor; storing a sequence of current measures most recently sampled; and determining a slope for the sequence of current measures by way of linear regression. Transmission of torque to the output spindle can be interrupted based in part on the slope of the current measures.