Measuring and testing – Dynamometers – Responsive to torque
Reexamination Certificate
2001-10-09
2003-07-29
Noori, Max (Department: 2855)
Measuring and testing
Dynamometers
Responsive to torque
Reexamination Certificate
active
06598491
ABSTRACT:
FIELD AND BACKGROUND OF THE INVENTION
This invention relates to a torque sensor, in general, and to a magnetoelastic torque sensor and a method for making such a torque sensor, in particular.
There are many applications where it may be desirable to sense the torsional stress applied to a torque-carrying member without contacting the member. In one type of apparatus for doing this, the torque-carrying member is surrounded by a magnetoelastic material, and a magnetic field detector is disposed adjacent to the magnetoelastic material for sensing changes in a magnetic field that passes through the material. These changes are indicative of torsional stresses within the torque-carrying member.
This type of magnetoelastic torque sensor is difficult to manufacture, costly, fragile and/or not well suited for rough-duty uses such as in the automotive and industrial fields.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an improved magnetoelastic torque sensor for measuring the magnitude of torque applied to a torque-carrying member and a method for making such a torque sensor.
According to a feature of the invention, a magnetoelastic torque sensor is provided with an inner flux guide with a projecting sense coil core.
According to another feature of the invention, a magnetoelastic torque sensor is provided with an inner flux guide made of magnetically conducting foil in a flat annular configuration with a projecting sense coil core tab.
It is yet another feature of the invention to simply form the inner flux guide, by cutting, stamping or etching to reduce production costs and provide other benefits.
It is further feature of the invention to provide a magnetoelastic torque sensor which utilizes a common material for both the inner flux guide and the sense coil core.
According to features of the invention, a non-contact, non-compliant torque sensor which is mechanically robust, highly reliable and extremely accurate is provided. A magnetoelastic element is disposed around the torque-carrying member and is fabricated by a thermal spraying process, wherein the magnetoelastic material is bonded onto the underlying torque-carrying member such as e.g. a torsion shaft member. In operation, torque applied to the shaft member is sensed by measuring changes in the magnetic field of the magnetoelastic material. These magnetic field changes occur in response to the torque applied to the shaft member which deforms the magnetoelastic material thereon resulting in a change of the magnetic field. The invention provides a torque sensor with a simple configuration and, with electronics of the magnetic pickup device, provides the sensor with unprecedented performance even when compared to more costly torque sensing devices.
The magnetoelastic torque sensor of the invention comprises an inner ferromagnetic flux guide encircling the shaft member in the vicinity of the magnetoelastic element, an outer ferromagnetic flux guide magnetically coupled to an outer edge of the magnetoelastic element, and a sense coil core, or preferably a plurality of sense coil cores, connecting the inner and outer flux guides. The sense coil core in conjunction with the flux guides acts as a main part of a magnetometer for measuring the magnetic flux from the flux generating source, namely the magnetoelastic material. The magnetic flux is collected and ducted to the sense coil cores via the inner and outer flux guides. Ferromagnetic material that has a square magnetic hysteresis loop is used for the cores of the sense coils. Amorphous metal materials (also commonly referred to as “Metglas” or “glass transition metal”) are preferably used at least for the construction of the sense coil cores.
According to another feature of the invention, in one embodiment an inner flux guide comprises a cylindrical ring structure (
FIG. 5
) fabricated from high permeability, low coercivity material generally referred to as Mu Metal. The ring structure has a pair of holes formed therein 180 degrees apart for receiving therein an amorphous wire which serves as the sense coil core. For the termination of the coil core to the outer flux guide which forms the flux return path, small notches are provided in the outer flux guide into which the amorphous wires extend.
According to a further feature of the invention, in a preferred embodiment a one-piece integral, inner flux guide and sense coil core is formed with at least one and preferably a single layer of amorphous metal foil having an annular configuration and at least one coil core tab in the same plane as that of the annular configuration.
The one-piece inner flux guide is supported, according to features of the invention, by cover and base pieces which are mounted about the shaft member so that the inner annular edge of the inner flux guide is slightly spaced apart from the magnetoelastic element. These cover and base pieces provide support for the metal foil, a substrate for printed electronic circuitry, mandrels of bobbins for centering the foil coil core tabs and for winding of the sense coils, and termination sites for coil wire connection to the electronic circuit while reducing the number of components to three. When assembled, the coil core tab is sandwiched between two complementary semi-cylindrical mandrel portions extending from the cover and base pieces. Coil wires are wound around the mandrel portions, which sense a change in the magnetic field of the magnetoelastic element as torque is applied to the shaft member.
Due to the one-piece amorphous metal foil serving as a combination flux guide and coil core material, a packaging is enabled with the single planar form of the foil. The flux guide foil formation is placed on a molded plastic carrier as the base piece, with its protruding tabs extending through the centers of the integral bobbins. A molded printed circuit board as the cover piece is positioned over the flux guide foil, with alignment features guaranteeing center hole concentricity and forming a sandwich to support and contain the amorphous foil formation. Molded protrusions from the circuit board complete the round winding mandrels of the bobbins, positioning the amorphous foil tabs in the center to serve as coil cores. The printed circuit board is extended in one region to allow the mounting and circuitry for interface electronic components and the electrical connector. This stack-together assembly greatly simplifies the manufacturing process and provides all of the essential features, the inner flux guide and its support (base and cover pieces), with essentially three elements.
According to a feature of the preferred embodiment of the invention, an approximately 0.001″ thick amorphous metal foil is laser cut or etched to form a flat ring with symmetrical, protruding coil core tabs spaced 180 degrees apart as the one-piece inner flux guide and sense coil core. This form of foil constitutes the inner flux guide for ducting flux from the source to be measured (e.g. the shaft and its magnetoelastic element which it encircles). It has been found that with very small cross sectional areas, even materials with relatively high magnetic saturation density characteristics will saturate at a modestly low point; also the saturation point will vary directly with cross sectional area. Given a constant material thickness (in this case about 0.001″), the saturation point will vary as a function of material width. An approximately 0.007″ diameter amorphous wire used as the sense coil core in the first embodiment is replaced by a strip of about 0.001″ thickness amorphous foil in the preferred embodiment. It has been found that a foil strip with a width of 0.040″ has a cross sectional area approximately equal to that of a 0.007 diameter wire, and produced similar performance to the wire core of the first embodiment when used as a coil core. The width of the foil tabs may range from about 0.030″ to 0.60″, and is optimum at 0.040″ (1 mm). The same parameters can be used with an amorphous material deposited on a suitable su
Kilmartin Brian
Opie John E.
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