Variable response rotary input control for a computer peripheral device

1. A user input device, comprising:

a rotary input control, comprising:

a wheel; and

an electropermanent magnet assembly, comprising:

a magnetizing coil, and

a permanent magnet coupled to the magnetizing coil and emitting a magnetic field; and

a control system configured to modulate an amount of electrical current supplied to the magnetizing coil to change a resistance profile within a linear torque region of the electropermanent magnet assembly for the rotary input control, the modulation switching the permanent magnet from a first state with a first resistance profile for freewheeling in which the magnetic field has a first magnetic flux and operates within the linear torque region to a second state with a second resistance profile in which the magnetic field has a second magnetic flux greater than the first magnetic flux and operates within the linear torque region, the magnetic field having a same polarity in both the first and second states,

wherein the control system modulates the amount of current supplied to the magnetizing coil based on a generated error signal corresponding to a difference measurement between a current supplied to the magnetizing coil and a new current setting corresponding to the second state; and

wherein the control system recalibrates an amount of current supplied to the magnetizing coil in the first state by measuring a rate of decay of an RPM of the wheel and using the rate of decay to establish a new baseline resistance.

2. The user input device as recited in claim 1 , wherein in the first state the resistance profile applies no force to the wheel, and wherein in the second state the resistance profile applies a ratcheting force to the wheel.

3. The user input device as recited in claim 1 , wherein in the first state the resistance profile is applied by interaction between a magnetic field emitted by the electropermanent magnet assembly and magnetically attractable materials of the wheel.

4. A user input device, comprising:

a rotary input control, comprising:

a wheel;

a magnetizing coil;

a first permanent magnet extending through the magnetizing coil;

a second permanent magnet, the first permanent magnet and the second permanent magnet being configured to set a resistance profile for the wheel by cooperatively emitting a magnetic field that is operable to oppose rotation of the wheel; and

a control system configured to switch between three or more different resistance profiles of the wheel by varying an amount of electrical current supplied to the magnetizing coil,

wherein at least two of the three or more different resistance profiles are of a same polarity and within a linear torque region of the first permanent magnet,

wherein the linear torque region of the first permanent magnet is between a minimum and maximum magnetic flux state for the first permanent magnet,

wherein the control system modulates the amount of current supplied to the magnetizing coil based on a generated error signal corresponding to a difference measurement between a current supplied to the magnetizing coil and a new current setting; and

wherein the control system recalibrates an amount of current supplied to the magnetizing coil in a first state by measuring a rate of decay of an RPM of the wheel and using the rate of decay to establish a new baseline resistance.

5. The user input device as recited in claim 4 , wherein the user input device is a mouse.

6. The user input device as recited in claim 1 wherein the generated error signal further controls a digital control and current steering system configured to control a current through a transistor network that sets the amount of current supplied to the magnetizing coil.

7. The user input device as recited in claim 6 wherein the transistor network includes two sets of bipolar junction transistors configured in parallel around the magnetizing coil.

8. The user input device as recited in claim 6 wherein the transistor network includes two sets of junction field effect transistors configured in parallel around the magnetizing coil.

9. The user input device as recited in claim 1 wherein the generated error signal is generated by a difference amplifier.

10. The user input device as recited in claim 9 wherein the new current setting is provided by a microprocessor and converted from a digital signal to an analog signal by a digital-to-analog converter.

11. The user input device as recited in claim 9 wherein the new current setting is provided by a microprocessor and converted from a digital signal to an analog signal by a pulse width modulator and integrator with filter circuit topology.

12. The user input device of claim 1 wherein the control system is further configured to:

receive revolutions-per-second (RPM) data corresponding to a free-wheeling friction associated with the wheel that is in rotation;

determine a rotational rate-of-decay of the wheel in rotation and a corresponding baseline resistance of rotation;

modulate an amount of electrical current supplied to the magnetizing coil in the electropermanent magnet assembly to change a torque curve for the wheel based on a difference between the rotational rate-of-decay and a reference rate-of-decay, the electropermanent magnet assembly providing a magnetic resistance to rotation of the wheel, and the torque curve providing one or more braking profiles for the wheel.

13. The user input device of claim 12 wherein the RPM of the wheel is tracked using a position sensor to measure rate of decay of the RPM.

14. The user input device of claim 12 wherein the wheel is a scroll wheel and the user input device is a computer mouse.