Stepping Motor Home Position Detection via Counter-EMF
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Solution Overview
Problem
Conventional display devices for vehicles require mechanical switches to determine the home position of reflectors, which are costly and less accurate at wide temperature ranges, such as -40 to +85°C.
Innovation Solution
A display device using a stepping motor with a microstep drive system and a gear mechanism that detects counter-electromotive power to determine the home position of a reflector without a mechanical switch, employing a stopper unit and control means to identify the reference position based on counter-electromotive signals.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a mechanical switch is used to determine the home position of the reflector, then the home position can be detected, but the cost increases and detection accuracy deteriorates at wide temperature ranges
Solution Approach 1:
The patent replaces the mechanical switch with an electrical detection system. The stepping motor's own electrical characteristics (counter-electromotive force, current changes) are utilized to detect the home position, eliminating the need for mechanical contact components that fail at extreme temperatures.
Solution Approach 2:
The system uses the stepping motor's inherent electrical properties to detect its own position. The motor serves both as the actuator and the sensor, detecting home position through changes in its electrical characteristics when the reflector contacts the stopper, thereby eliminating separate detection components.
2Measurement precision
If a mechanical switch is used to determine home position, then position detection is achieved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the home position detection function from the mechanical switch and integrates it into the control system through electrical sensing. This removes the separate mechanical detection component and its associated complexity while maintaining the detection capability.
Solution Approach 2:
The control system performs multiple functions: it controls the stepping motor's operation and simultaneously detects the home position by monitoring the motor's electrical characteristics. This multi-functionality eliminates the need for separate detection hardware, reducing overall system complexity.
3Measurement precision
If a mechanical switch is used for home position detection, then the reference position can be determined, but reliability decreases due to mechanical wear and temperature sensitivity
Solution Approach 1:
The patent substitutes electrical sensing for mechanical switching. By monitoring electrical parameters (current, counter-electromotive force) of the stepping motor, the system determines the reference position without mechanical contact, eliminating wear and temperature-related failures.
Solution Approach 2:
The system continuously monitors the stepping motor's electrical characteristics during operation and uses this feedback to determine when the home position is reached. This electrical feedback mechanism is more reliable than mechanical switches as it has no moving parts that can wear or fail under extreme conditions.
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
Enables accurate determination of the home position of a reflector without a mechanical switch, reducing costs and improving reliability across varying temperatures.
Implementation Method 1
the drive means has a function of detecting counter-electromotive power that is generated in the stepping motor when the moving part abuts against the stopper unit
Implementation Method 2
a reflector for reflecting the display light emitted by the display unit toward the light transmitting member
Data Source
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AI summary
The origin (reference position) of a reflector moved by a stepping motor is determined without using a mechanical switch. This display device is provided with: a stepping motor (41); a concave mirror (31) that moves in accordance with the operation of the stepping motor (41), the concave mirror (31) reflecting display light emitted from a display unit toward the windshield; a lever part (33) that moves together with the concave mirror (31) ; a drive unit for driving the stepping motor (41) by a microstep drive system; a control unit for controlling the movement of the concave mirror (31) by controlling the drive unit; and a stopper unit (44) provided within the range of movement of the lever part (33). The drive unit has a function for detecting the counter-electromotive force generated by the stepping motor (41) when the lever part (33) comes into contact with the stopper unit (44). The control unit determines the reference position when the movement of the concave mirror (31) is controlled in accordance with the counter-electromotive force detected by the drive unit.