Electricity: measuring and testing – Magnetic – Displacement
Reexamination Certificate
1998-12-14
2001-02-27
Strecker, Gerard (Department: 2862)
Electricity: measuring and testing
Magnetic
Displacement
C324S207200, C029S595000
Reexamination Certificate
active
06194894
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns an angle-of-rotation sensor with a stationary component and a rotating component. The stationary component includes a stator accommodated in a housing with at least one base. The stator is in two halves of ferritic material separated by space and each provided with at least one 45° bevel. The rotating component includes an annular magnet accommodated in a holder and rotating around the stator with an airgap left between them.
An angle-of-rotation sensor of this genus is known from the WIPO Patent Publication No. WO A 95/14911, which is assigned to the present applicant. It comprises a stationary component and a rotating component that moves in relation to it. The stationary component has two mutually facing stator halves with space between them. Each stator half is a stack of sheetmetal disks secured against the bottom of the housing by a tensioning component. The rotating component includes an annular magnet accommodated in a holder.
There are drawbacks to this embodiment. The stacks are expensive to manufacture and secure. The magnet holder is designed such that the magnet is not magnetically insulated from a shaft that the rotating component is fastened to, contaminating the outgoing signals. Furthermore, the poles of the magnet are difficult to position properly with respect to the space between the stator halves while the sensor is being assembled.
SUMMARY OF THE INVENTION
The principal object of the present invention is accordingly to provide a more accurate angle-of-rotation sensor of the aforesaid genus that will be easier to manufacture and assemble. The stationary component in particular will be simpler, the magnet holder as magnetically insulating as possible, and the annular magnet reliably secured in the holder and easy to position precisely with respect to the space between the stator halves and the stationary component.
This object, as well as other objects which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, in an angle of rotation sensor of the type described above, by the following features:
(a) the ferritic stator halves are sintered stator halves, with at least one holder secured in a stabilizing cutout in a baseplate of non-magnetic material;
(b) the magnet holder is a metal-injection molded holder with at least one partly magnetically insulating section and with at least one cut-out gap; and
(c) the magnet is positioned in the holder by at least one cut-out gap and at least one matching web at a specified angle (&agr;) to the space.
The present invention has several advantages. Stators are easy to sinter, precise and stable. The complicated stacking procedure is eliminated. One particular advantage is that each sintered stator half can be fastened to the baseplate extremely accurately. The magnet holder can be cost effectively and, in particular, precisely fabricated by metal-injection molding (MIM). Complicated additional shaping, especially machining, of the material is unnecessary. The holder will hold the magnet exactly where it should be within precise tolerances. Measurements will be considerably more precise. The web or space will simultaneously position the magnet precisely in relation to the space during assembly. No complicated readjustments will be necessary. It will accordingly be possible to position the magnet's pole at a right angle, perpendicular that is, to the space between the two facing stator halves. If any angle other than a right angle is needed in special cases, it can be established ahead of time for all the angle-of-rotation sensors in the same series. Most significant, however, is that the magnet will be secured too tighty to turn.
Two alternative embodiments of the stator holders are possible. They can be either sintered bolts or sintered feet. Whether bolts or feet, they can terminate in a sintered cap. This feature ensures that the sintered stator half is secured, stationary, in the baseplate.
The baseplate can be a stator baseplate with at least one stabilizing cutout.
Two alternative embodiments of the stator baseplate are possible.
The stator baseplate can comprise the base of the stationary-component housing and have stabilizing cutouts with sintered stator halves fitting into it along with their feet and caps.
The stator baseplate can alternatively be a stabilizing disk with at least one stabilizing cutout and at least partly surrounded by a fastener with at least one fastening cutout.
At least the stabilizing disk can be at least partly surrounded by the base of the housing.
The second embodiment of the stabilizing cutouts and the fastening cutouts can be round or orange-segment shaped.
The stator baseplate can be aluminum, copper, or plastic.
The various embodiments of the baseplate can secure the sintered stator halves in two different ways.
In the first approach, the halves can be sintered to final dimension, finally positioned, and forced into the base of the housing as a whole. The essential advantage of this approach is the extremely cost-effective stabilization and fastening of the halves. The stationary component can accordingly be finally fabricated in only two basic steps.
In the second approach, the basic components of the stator are metal-injection molded of a ferritic material and the stator baseplate metal-injection molded, especially of aluminum, around the stator half. The resulting blank is removed from the mold and both the half and baseplate sintered in a furnace, both metals contracting. This process will ensure that the half fits into the baseplate, tight and precise, and cannot be displaced by even powerful forces.
The accordingly sintered molding is then inserted into a molded housing and secured therein, either resiliently or at least to some extent by encapsulation.
The housing and its base can be of plastic, preferably injection-molded to ensure that the stationary component constitutes a precisely dimensioned component of the sensor.
Two alternative embodiments of the metal-injection molded holder are possible.
It can be a cup metal-injection molded in one piece of magnetic material with an essentially round foot, at least two, preferably cylindrical stems rising out of one edge of the foot, and an essentially round and hollow bowl resting on the stems. A one-piece bowl is considerably less expensive to manufacture. Such a cup can be molded of magnetic material in a single mold. The molding will be 30 percent oversize and will need to be heated and sintered to its final dimensions. To allow at least extensive magnetic insulation of the cup from the components to be mounted on it, the stems can magnetically insulate the foot from the bowl.
The holder can alternatively be metal-injection molded in two parts, comprising an essentially straight-sided bowl with a round base of metal-injection molded of a non-magnetic material, provided in a second molding stage with a cylindrical wall of magnetic material. The resulting bi-material molding will be 30 percent oversize and will need to be more or less sintered to its final dimensions. The base and wall will accordingly be precisely dimensioned and will fit together perfectly tightly. The wall will be precisely positioned. The non-magnetic material of the base will ensure effective magnetic insulation from any components to be mounted on the bowl. One particular advantage is that the base of the bowl can be provided with a cutout that will readily accommodate a simply inserted valve shaft. This feature will compensate for the extra expense of two-part manufacture.
A gap can be cut out of the bowl in either embodiment. If the magnetic wall is provided with at least one matching web, the poles of the wall can be positioned at a right angle, perpendicular that is, to the space between the mutually facing stator halves. If, in a special case, the angle is to be other than a right angle, it can be precisely established for all the products in a single series.
The web or webs can be positioned near at least one of the joints betwe
Apel Peter
Hauschopp Marion
AB Eletronik GmbH
Milde Hoffberg & Macklin, LLP
Strecker Gerard
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