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US 6,591,688 B2Granted
Load sensing by partial magnetic saturation
AssigneeStarr-Johnson
InventorHubert A. Wright
Life of this patent
Estimating the term…
Abstract
A load applied to a load cell's load-bearing member (21) causes that member to move against the force applied by springs (28 and 30) and thereby bring a magnet (24) into closer proximity to the ferromagnetic core (12) of a coil (10). Acting across a small gap, the magnet partially saturates a magnetic circuit that encloses the coil. This force-caused magnet motion changes the coil inductance and the magnetic circuit's degree of saturation. By applying to the coil (10) a brief voltage pulse without thereby heating it significantly, and by observing the coil current's resultant steady-state value and the rate at which the coil current approaches that value, an inductance-to-load converter (FIG. 4) calculates the applied load and the coil's temperature and generates outputs that represent them.
Claims41
A load transducer comprising:
- A) a load cell including:
- i) a high-permeability path material forming an at least partially saturable high-permeability path portion of a closed magnetic path in which the high-permeability portion is interrupted by a relatively low-permeability path portion shorter than the high-permeability portion;
- ii) a permanent magnet generally aligned with the path and mounted in the low-permeability path portion for such resilient relative movement between the magnet and at least part of the high-permeability path portion upon application of load to the load cell as to change the degree of magnetic saturation of the magnetic path, the total length of the low-permeability path portion, exclusive of the magnet, being less than four times the thickness of the magnet in the path direction;
- and
- iii) an electrically conductive coil so linked to the magnetic path that the inductance of the coil depends on the reluctance of the magnetic path, whereby the inductance of the coil depends on the load applied to the load cell;
- and
- B) an inductance-to-load converter, connected to the coil, that measures a coil-inductance-dependent quantity, determines the load from the coil-inductance-dependent quantity, and generates an output indicative of the load thereby determined.
4 more elements
A load transducer comprising:
- A) a load cell including:
- i) a high-permeability path material forming an at least partially saturable high-permeability path portion of a closed magnetic path in which the high-permeability portion is interrupted by a low-permeability path portion, the length of the high-permeability path portion being at least five times the length of the low-permeability path portion;
- ii) a permanent magnet generally aligned with the path and mounted in the low-permeability path portion for such resilient relative movement between the magnet and at least part of the high-permeability path portion upon application of load to the load cell as to change the degree of magnetic saturation of the magnetic path;
- and
- iii) an electrically conductive coil so linked to the magnetic path that current flowing through the coil induces in the magnetic path a magnetic flux that depends on the reluctance of the magnetic path, whereby the inductance of the coil depends on the load applied to the load cell;
- and
- B) an inductance-to-load converter, connected to the coil, that measures coil-inductance-dependent quantity, determines the load from the coil-inductance-dependent quantity, and generates an output indicative of the load thereby determined.
4 more elements
A method for measuring load comprising:
- A) providing a load cell that includes:
- i) a high-permeability path material forming an at least partially saturable high-permeability path portion of a closed magnetic path in which the high-permeability portion is relatively long and interrupted by a relatively small low-permeability path portion;
- ii) a permanent magnet generally aligned with the path and mounted in the low-permeability path portion for such resilient relative movement between the magnet and at least part of the high-permeability path portion upon application of load to the load cell as to change the degree of magnetic saturation of the magnetic path, the length of the low-permeability path portion, exclusive of the magnet, being less than four times the thickness of the magnet in the path direction;
- and
- iii) an electrically conductive coil so linked to the magnetic path that current flowing through the coil induces in the magnetic path a magnetic flux that depends on the magnetic reluctance of the path, whereby the inductance of the coil depends on the load applied to the load cell;
- B) measuring a coil-inductance-dependent quantity;
- C) determining the load from the coil-inductance-dependent quantity;
- and
- D) generating an output indicative of the load thereby determined.
6 more elements
A method for measuring load comprising:
- A) providing a load cell that includes:
- i) a high-permeability path material forming an at least partially saturable high-permeability path portion of a closed magnetic path in which the high-permeability portion is relatively long and interrupted by a relatively small low-permeability path portion, the length of the high-permeability path portion is at least five times the length of the low-permeability path portion;
- ii) a permanent magnet generally aligned with the path and mounted in the low-permeability path portion for such resilient relative movement between the magnet and at least part of the high-permeability path portion upon application of load to the load cell as to change the degree of magnetic saturation of the magnetic path;
- and
- iii) an electrically conductive coil so linked to the magnetic path that current flowing through the coil induces in the magnetic path a magnetic flux that depends on the reluctance of the magnetic path, is whereby the inductance of the coil depends on the load applied to the load cell;
- B) measuring a coil inductance-dependent quantity;
- C) determining the load from the coil-inductance-dependent quantity;
- and
- D) generating an output indicative of the load thereby determined.
6 more elements
Dependencies are inferred from the claim text.