Magnetic navigation system with soft magnetic core electromagnets for operation in the non-linear regime

Patent metadata

Field	Value
Publication number	US-9681859-B2
Application number	US-201314381723-A
Country	US
Kind code	B2
Filing date	Feb 26, 2013
Priority date	Feb 28, 2012
Publication date	Jun 20, 2017
Grant date	Jun 20, 2017

Abstract

A magnetic manipulation and navigation system for moving a magnetic element through a body comprising at least six electromagnets with soft-magnetic cores arranged in a predetermined position to the body. One or more of the electromagnets operate in the non-linear regime of the magnetization curve of the cores. At least one magnetic field sensor is at one or more predetermined positions outside of the operating region. In the linear region, no feedback is required to set the magnetic field strength. In the non-linear region, feedback from the magnetic field sensors is used for closed-loop control. The system has an open loop mode operation in the linear regime for fast control signals, for stabilization during displacement of the magnetic element, and a closed-loop operation in the non-linear regime for higher field strengths, to apply forces and moments on the magnetic element while it is in contact with a surface.

First claim

The invention claimed is:

1. A magnetic manipulation and navigation system for moving a magnetic element through a body comprising:
at least six electromagnets fixed in predetermined relation to said body; and
a control unit supplying current for the electromagnets,
wherein the electromagnets have electromagnetic coils and soft magnetic cores,
wherein the soft magnetic cores each have a magnetization curve comprising a central linear region and a non-linear region,
wherein the control unit comprises a first operating mode and a second operating mode,
wherein in the first operating mode, the current supplied by the control unit to each of the electromagnets is configured to operate the electromagnetic coils of each of the electromagnets in the central linear region of the magnetization curve of respective cores as a linear regime,
wherein in the second operating mode, the current supplied by the control unit to each of the electromagnets is configured to operate the electromagnetic coils of one or more of the electromagnets in the non-linear region of the magnetization curve of the respective cores as a non-linear regime, and
wherein the first operating mode is an open-loop mode operation in the linear regime and the second operating mode is a closed-loop operation in the non-linear regime.

2. The system according to claim 1 , comprising at least one magnetic field sensor at a predetermined position outside of a navigating region of the magnetic element through the body,
wherein during operation in the first operating mode the control unit controls the current in absence of a feedback signal, and
wherein during operation in the second operating mode the control unit controls the current using feedback from the at least one magnetic field sensor for closed-loop control.

3. The system according to claim 2 , wherein the control unit is configured to switch from the first operating mode to the second operating mode upon reception of a sensor signal from the magnetic field sensor and relating to the magnetic element.

4. The system according to claim 1 , wherein each electromagnet has a negative and a positive saturation value of flux density, wherein the central linear regions of the electromagnets are delimited by the negative and positive saturation values of the flux density of each electromagnet being in an interval between the negative and positive saturation value of each electromagnet, delimited at a threshold value of the negative and positive saturation value of each electromagnet chosen from the group of threshold values at 70%, 80% or 90%.

5. The system according to claim 4 , wherein the soft magnetic cores of the electromagnets have a saturation magnetisation of more than 1 T, and a coercivity below 1000 A/m.

6. The system according to claim 5 , wherein the soft magnetic cores of the electromagnets have a saturation magnetisation of more than 2 T, and a coercivity less than 300 A/m.

7. The system according to claim 1 , wherein each electromagnet has an aspect ratio of width to length, and
wherein the aspect ratio of width to length of each electromagnet is between 4 and 10.

8. The system according to claim 1 , wherein the magnetic element has a position and orientation inside the body, and
wherein the control unit is connected to a localization unit, configured to detect the position and orientation of the magnetic element inside the body.

9. The system according to claim 8 , wherein the localization unit has an output signal, wherein the output signal of said localization unit is connected to a closed-loop module of the control unit for use within the second operating mode.

10. The system according to claim 1 , wherein the at least six electromagnets are eight electromagnets,
wherein a first group of four electromagnets of the eight electromagnets is arranged approximately in a plane, each of the electromagnets of said first group having an angular distance of between 80 to 100 degrees one from another,
wherein a second group of four electromagnets of the eight electromagnets are all inclined in an angle of between 35 to 55 degrees against the plane of the first group, each of the electromagnets of said second group having an angular distance of between 80 to 100 degrees one from another, and
wherein the electromagnets of said first group and said second group are regularly spaced at between 35 to 55 degrees, one from another.

11. The system according to claim 1 , wherein the at least six electromagnets are six electromagnets,
wherein a first group of three electromagnets of the six electromagnets is arranged approximately in a plane, each of the electromagnets of said first group having an angular distance of between 110 to 130 degrees one from another,
wherein a second group of three electromagnets of the six electromagnets are all inclined in an angle of between 35 to 55 degrees against the plane of the first group, each of the electromagnets of said second group having an angular distance of between 110 to 130 degrees, one from another, and
wherein the electromagnets of said first group and said second group are regularly spaced at between 50 to 70 degrees one from another.

12. The system according to claim 1 , wherein the at least six electromagnets are six electromagnets,
wherein a first group of three electromagnets of the six electromagnets is arranged below a plane, all inclined in an angle of between 35 to 55 degrees against said plane, and all having an angular distance of between 110 to 130 degrees one from another in view of said plane,
wherein a second group of three electromagnets of the six electromagnets are all inclined in an angle of between 35 to 55 degrees against said plane opposite to the first group, each of the electromagnets of said second group having an angular distance of between 110 to 130 degrees one from another,
wherein the electromagnets of the first group and the second group are regularly spaced at between 50 to 70 degrees one from another.

13. The system according to claim 1 , wherein the at least six electromagnets are eight electromagnets,
wherein a first group of four electromagnets of the eight electromagnets is arranged above a plane, all inclined in an angle of between 20 to 40 degrees against said plane, and all having an angular distance of between 80 to 100 degrees one from another in view of said plane,
wherein a second group of four electromagnets of the eight electromagnets are arranged above said plane, all inclined in an angle of between 35 to 55 degrees against said plane, each of the electromagnets of said second group having an angular distance of between 80 to 100 degrees one from another, wherein the electromagnets of the-said first group and the-said second group are regularly spaced at between 40 to 50 degrees one from another.

14. The system according to claim 1 , wherein the control unit is configured to provide a calibration mode, within which every single one of the electromagnets is supplied one after the other with a predetermined current and a magnetic field sensor senses an effect in situ in said body;
wherein a resulting magnetic field within said body upon supply of said predetermined current to all said electromagnets is determined, and
wherein the control unit generates control signals for the electromagnets in the linear region around said predetermined current for use in the first operation mode.

15. The system according to claim 1 , wherein a portion of each core of the electromagnets directed towards the workspace body is bare for a length equivalent to the radius of each core, followed by a tapered coil arra

Assignees

• Eth Zuerich

Inventors

• Muntwyler Simon
• Kratochvil Bradley
• Nelson Bradley
• Frutiger Dominic
• Bell Dominik
• Baumann Jonas

Classifications

• A61B34/30

  Surgical robots · CPC title

• A61B2017/00876

  magnetic · CPC title

• A61B2017/00039

  Electric or electromagnetic phenomena other than conductivity, e.g. capacity, inductivity, Hall effect · CPC title

• A61B34/70

  Manipulators specially adapted for use in surgery · CPC title

• A61F9/007

  Methods or devices for eye surgery · CPC title