Haptic Driver Circuit Using Pulsed Current and Recirculation Diode
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Solution Overview
Problem
Classical driver circuits for electromagnetic and electro-permanent magnets in haptic devices dissipate a lot of energy and suffer from Electro-Magnetic Interference (EMI), as they continuously monitor and control current, leading to unwanted oscillations and inefficient energy use.
Innovation Solution
A driver circuit that cuts off the current once it reaches a desired level, using a fast switching circuit with an H-bridge transistor switch and a diode for recirculation, allowing for efficient energy conservation and reduced EMI by maintaining 80% of the capacitor charge for the next pulse.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If continuous current monitoring and control is used, then precise electromagnetic force control is achieved, but energy consumption increases and EMI occurs
Solution Approach 1:
The patent implements periodic pulsed current delivery instead of continuous current control. The capacitor charges to a peak voltage and then discharges through the electromagnet in controlled pulses, creating periodic action that reduces average power consumption while maintaining the ability to precisely control electromagnetic force during each pulse cycle
Solution Approach 2:
The capacitor is pre-charged to a peak voltage before each current pulse is delivered to the electromagnet. This preliminary charging action stores energy in advance, allowing the system to deliver high current pulses without continuous power consumption, thereby reducing overall energy usage while maintaining control precision
2Force
If continuous current control is used, then electromagnetic force is maintained, but energy is dissipated and EMI is generated
Solution Approach 1:
The system uses periodic pulsed current delivery where the capacitor charges and discharges in cycles. During each cycle, the electromagnet receives current only during the discharge phase, creating periodic electromagnetic force that maintains actuation while minimizing continuous energy dissipation and reducing EMI generation
Solution Approach 2:
The patent converts the natural inductive kickback and voltage transient that normally cause EMI and energy loss into a beneficial feature by using a freewheeling diode. The diode provides a controlled path for the inductive current, converting potential harmful voltage spikes into useful continued current flow that maintains electromagnetic force while preventing EMI
3Measurement precision
If fast switching is used, then current cutoff precision is improved and energy is conserved, but switching losses increase
Solution Approach 1:
The patent extracts the switching function from continuous control and implements it only at critical moments - when the capacitor reaches peak voltage and when current needs to be cutoff. This selective switching approach minimizes the duration of switching operations, reducing total switching losses while maintaining precise current cutoff control for energy conservation
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
This approach reduces power consumption and eliminates oscillations, maintaining 80% of the capacitor charge for the next pulse, leading to more efficient energy use and minimized EMI, while ensuring precise control over the electromagnetic force.
Implementation Method 1
The energy reservoir can be a capacitor which can be charged sufficiently to deliver many dozens of amperes
Implementation Method 2
connect a charged capacitor through a switch to the inductive windings of an electromagnet
Implementation Method 3
a diode is provided in parallel with an electro-permanent magnets (EPM) winding when the current is shut off, providing a recirculation path that prevents the voltage transient across the EPM terminals
Data Source
AI summary
A driver circuit is provided to connect a charged capacitor through a switch to the inductive windings of an electromagnet for a haptic feedback application. A feedback circuit provides an indication of the current supplied. When the current reaches a desired level, the current is cut off, rather than being controlled. The cutoff level can be slightly below the desired level to allow the desired level to be reached with overshoot. A diode is provided in parallel with the electromagnet winding when the current is shut off, providing a recirculation path that prevents the current from being discharged, thereby dissipating less energy than classical solutions.