Brushless DC Motor Sinusoidal Drive for Massage Machines
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing massage machines face challenges in using small-sized, high-torque motors that minimize acoustic noise and maintain accurate rotation speed control, especially when dealing with varying loads, which affects the comfort and effectiveness of three-dimensional treatment trajectories.
Innovation Solution
A massage machine design incorporating small-sized, high-torque brushless DC motors with a control circuit that adjusts the drive signal waveform to sinusoidal, allowing for independent control of motors and precise rotation speed management, ensuring comfortable and accurate three-dimensional trajectory tracing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a high torque brushed DC motor is used, then the motor has high torque capability, but the motor has large external shape and heavy weight
Solution Approach 1:
The patent replaces the brushed DC motor (mechanical contact system with brushes and commutators) with a brushless DC motor (electronic commutation system). This substitution eliminates the mechanical brushes while maintaining the motor's torque capability, resulting in reduced weight and size without sacrificing the force output required for the massage machine's three-dimensional trajectory control.
2Power
If a general 3-phase 4-pole brushless DC motor is driven by 120-degrees rectangular wave current, then the motor achieves high torque output, but the torque significantly varies due to cogging causing large acoustic noises
Solution Approach 1:
The patent changes the drive waveform parameter from 120-degrees rectangular wave to sinusoidal wave. This parameter change smooths the current delivery to the motor windings, eliminating the abrupt transitions that cause cogging torque variations and acoustic noise, while maintaining the motor's high torque output capability through optimized sinusoidal control.
3Object-affected harmful factors
If a brushless DC motor is controlled by sinusoidal wave driving, then low noise and low vibration are achieved, but it requires high accuracy rotation angle detection with encoder increasing cost, size and weight
Solution Approach 1:
The patent extracts and eliminates the encoder component from the brushless DC motor control system. Instead of using high-accuracy rotation angle detection with encoders, the invention implements a sensorless control method that estimates rotor position and speed through current sensing and mathematical modeling, thereby achieving sinusoidal wave control without the added cost, size, and weight of encoder hardware.
4Object-affected harmful factors
If sinusoidal wave drive is applied to brushless DC motor, then low noise operation is achieved, but the motor cannot start or difficult to smoothly start because load is not constant
Solution Approach 1:
The patent applies preliminary action by implementing a two-stage starting sequence: first, the motor is started using rectangular wave current which provides high starting torque and handles the constant load condition effectively; second, after the motor reaches a predetermined rotational speed, the control transitions to sinusoidal wave current for noiseless operation. This preliminary rectangular wave starting action resolves the starting difficulty while preserving the low-noise benefit during normal operation.
5Speed
If brushed DC motor is used for short time switching between low speed and high speed rotation, then the motor can switch rotation speed in short time, but the motor has large external shape and heavy weight
Solution Approach 1:
The patent replaces the brushed DC motor's mechanical speed control system (with brushes and commutators) with a brushless DC motor equipped with electronic control. The electronic control system enables rapid switching between low speed and high speed rotation through PWM (pulse width modulation) and variable frequency drive, achieving the same speed switching capability as brushed motors but with significantly reduced weight and size due to the elimination of heavy mechanical components.
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 solution reduces motor noise and vibration, enabling comfortable massage effects by maintaining accurate rotation speed control and sinusoidal current flow, even with load variations, thus enhancing user experience.
Implementation Method 1
a brushless DC motor, and a control circuit for driving the brushless DC motor
Data Source
AI summary
A massage machine using a small size and high torque brushless DC motor includes a driving unit moved up and down along guide rails of a chair and a first motor for moving the driving unit up and down. A pair of treatment head bases are driven reciprocally in opposite directions to each other; and a second motor reciprocally drives the treatment head bases in opposite directions to each other. Treatment heads are respectively supported by the treatment head bases; and a third motor drives the treatment heads in a plane substantially perpendicular to a backrest. A control circuit drives the respective motors respectively independently of one another. Each motor is a brushless motor. A control circuit corrects, corresponding to a load imposed on the brushless DC motor, a waveform of a drive signal applied to a winding of the brushless DC motor so as to allow a current flowing through the winding of the brushless DC motor to have a substantially sinusoidal waveform making it possible to reduce discomfort due to motor noise, and to accurately control the motor rotation speed.