Electric Scissors Forced Stop Device Hardware Safety

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Solution Overview

Problem

Electric scissors with motor-controlled blades can operate unintentionally due to CPU malfunctions, leading to unintended cutting operations when the control device fails or malfunctions.

Innovation Solution

Incorporating a forced stop device with a hardware-based stop signal output unit and stop circuit that independently stops the motor when an abnormal state is detected, ensuring the blades do not operate against the user's intention by interrupting power supply regardless of control signals.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of operation

If the motor is controlled by a CPU based on software control, then the blades can be finely adjusted by operating the trigger, but the blades may operate unintentionally when the CPU malfunctions

Engineering Contradiction:

Improvefine adjustment of blade movementVSAvoidunintended blade operation due to CPU failure

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

A hardware-based forced stop device is introduced as an intermediary between the control system and the motor. This device includes a stop signal output unit that generates a stop signal when detecting abnormal states, and a stop circuit that receives this signal to interrupt power supply to the motor, thereby preventing unintended operation while preserving normal software control functionality

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent replaces purely software-based control with a hybrid system that incorporates hardware-level intervention. The forced stop device uses hardware circuits to detect abnormal states and physically interrupt power supply, substituting the need for software reliability with a dedicated hardware safety mechanism

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Reliability

If a forced stop device is added to prevent unintended motor rotation, then safety is improved, but the device complexity increases

Engineering Contradiction:

Improveprevention of unintended blade operationVSAvoidadditional forced stop device components

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The forced stop function is extracted as a separate, independent device from the main control system. The stop signal output unit and stop circuit are implemented as distinct hardware components that operate independently, allowing the safety function to be added without complicating the existing software control architecture

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The forced stop device uses simple, inexpensive hardware components such as comparators, logic circuits, and power interruption switches. These components are designed for single-purpose safety functionality with minimal complexity, providing reliable protection without significant cost or complexity overhead

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

Data Source

PatentEP3127665B1Electric scissors

Publication Date: 2020.03.18 MAKITA CORP

Figure 1A~1B
Figure 2A~2C
Figure 3

AI summary

Electric scissors (1) comprise a motor (10), a movable blade (3), a transmission mechanism (12, 16), an operation device (6), an operation signal output device (20), a control device (32), a drive circuit (31), and a forced stop device (32). The forced stop device (32) is configured to stop the motor (10) when an abnormal state is present in which the value of the operation signal (St) output from the operation signal output device (20) is a value determined in the control device (32) to rotate the motor (10) in a specific rotation direction out of the first and the second rotation directions or to stop the motor (10), and in which the motor (10) is rotating in a direction opposite to the specific rotation direction.