Hose Reel Back-EMF Control for Constant Retraction Speed
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Solution Overview
Problem
Conventional motor-driven hose reel assemblies lack control over hose retraction speed, leading to increased speed at the end of the retraction process, which can cause the hose to be ripped out of the user's hands or result in damage due to the stopper striking the reel with large momentum.
Innovation Solution
A control system that utilizes Back EMF measurements during inactive phases of the motor to determine the unwound hose length and regulate the retraction speed, ensuring a constant hose retraction speed by adjusting the motor speed based on calculated hose length, using a DC motor and Puls-Width-Modulation (PWM) to extend measurement periods without affecting performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the motor rotational speed is kept constant during hose retraction, then the motor operation is simple, but the hose retraction speed increases at the end stage causing the hose to rip out of user's hands and potential damage to the reel assembly
Solution Approach 1:
The motor rotational speed is dynamically adjusted based on the unwound hose length. The controller varies the motor speed to maintain constant hose retraction speed, transitioning from high speed when hose diameter is small to lower speed as hose diameter increases during retraction
Solution Approach 2:
The system uses Back EMF measurement to detect motor speed and calculate unwound hose length in real-time. This feedback information is used by the controller to continuously adjust motor rotational speed, creating a closed-loop control system that maintains constant hose retraction speed
2Speed
If the hose retraction speed is controlled by knowing the unwound hose length, then the hose retraction speed can be regulated, but the system complexity increases due to the need for Back EMF measurement and calculation
Solution Approach 1:
The motor itself generates the measurement signal through Back EMF during its normal operation. The controller utilizes this naturally occurring electrical phenomenon to determine motor speed and calculate hose length without requiring external sensors or additional measurement devices
Solution Approach 2:
The Back EMF voltage serves as an intermediary that connects motor rotational speed to hose length calculation. By measuring this electrical parameter and integrating it over time, the system derives mechanical displacement information without direct mechanical measurement
3Measurement precision
If the Back EMF is measured continuously, then the motor speed determination is accurate, but the measurement interference with motor operation increases
Solution Approach 1:
The controller measures Back EMF periodically during inactive phases when power supply to the motor is temporarily interrupted. This pulsed measurement approach provides sufficient data for speed determination while minimizing interference with overall motor operation and energy consumption
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
The control system effectively maintains a constant hose retraction speed, preventing undesired increases and reducing the risk of hose damage, by accurately determining the unwound hose length and adjusting the motor speed accordingly, allowing for precise control of the hose retraction process.
Implementation Method 1
the measurement and thus exploitation of the so called Back Electro-Motive Force (Back EMF) that is the voltage which is opposite in polarity, created by the rotation of a coil in a magnetic field. Thus the Back EMF is the voltage generated during the operation of a rotating motor.
Data Source
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AI summary
A control system (200) for a hose reel assembly (100) includes a motor (210), a power supply unit (230), and a controller (220) for controlling supply of power to the motor (210). The controller (220) stops the supply of power to the motor (210) for a pre-determined time-period (T) and allows the motor (210) to run. The controller (220) measures Back EMF during the pre-determined time-period (E). The control system (200) is characterized in that the controller (220) is configured to determine a first time instant (T1) and a second time instant (T2) for measuring Back EMF. The first time instant (T1) and the second time instant (T2) is different from each other. The controller (220) further determines the motor speed (S) based on the measured Back EMF at the first time instant (T1) and the second time instant (T2).