The invention relates to a sensor magnet according to the preamble of
Claim 1 and further relates to a magnetizing coil for the
Angles and absolute positioning are used in measuring and automation technology
so far mainly optical measuring systems
used. Although these measuring systems
have a high accuracy, they prove under harsh operating conditions
as susceptible to failure. In the last
Time is therefore attempted to such measuring systems on the basis of
Form magnetic field sensors and multi-pole magnetized permanent magnet.
The coding of the sensor magnets is carried out by means of an impressed north-south pole pattern
on one or more tracks. The location of North and South Poland can
evaluated with one or more digital magnetic field sensors
become. However, practice has shown that when not symmetrically magnetized
Permanent magnets (wide and narrow north or south poles as immediate or
indirect neighbors) there is a shift in field strength and
the steepness of the flanks of the induction curve in a defined
Distance (position of the sensor) comes in the area of north-south transitions.
is added that the
for use coming magnetic field sensors a switching hysteresis
own and thus also a certain inaccuracy in the evaluation
cause the position. These physical processes have one
direct influence on
the accuracy and use of such positioning systems.
by virtue of
the switching hysteresis, this magnetization should be as possible
Field gradients nearby
have the switching sensitivity of the sensor magnet.
In addition to this
It should be noted that in increasing
Dimensions of permanent magnets
in combination with a sensor element (eg Hall sensor, field plate,
GMR or GIANT MAGNETO RESISTANT sensor or similar) can be used for position detection.
This can be a linear displacement between magnet and sensor
or even a rotary motion of a magnet rotor at the front
or lateral magnetization.
The European patent application EP 0 718 494 A2
relates to an apparatus for magnetizing a magnetic material for producing magnetic poles of nonuniform strength in a magnetic encoder. The described magnetization device is designed such that in the magnetization pattern of the coder the north pole is symmetrical with the maximum magnetization in the middle between the pole junctions, while the maximum magnetization of the south pole is shifted towards a pole transition.
Many applications have high accuracy requirements
the position of the pole transition
posed. This transitional sharpness will
generally determined by the accuracy of the magnetizing coil.
are instead of regular switching patterns
same pole width irregular switching pattern
demanded, that is
the width of the poles, about
which the switching state of the sensor defined on or off
is, varies from pole to pole. Even with arbitrary exact magnetization
This is by the law
the stray fields magnetostatically the zero crossing of the detected induction
between the poles opposite
moved the magnetization change. The shift is down
other from the measuring distance
so that too
with exact magnetization the switching points opposite to their
ideally located. The same problem occurs
multi-track magnetizations on which the poles of the neighboring tracks
the zero crossing over
to move a track.
Invention is based on the object, the magnetization of the sensor magnet
to influence in the development of such positioning systems so
Displacement is reasonably least, and a magnetization
in which the stray field effect of wide poles is only marginal
located Polübergänge acts.
According to the invention
this task is solved by
Switching range of the sensor magnet in the middle between the pole transitions
has greatly reduced magnetization and the magnetization
is highest in the area of pole transitions
and there as possible
quickly reversing in the direction.
advantageous developments of the invention are in the claims 2 to
9 marked while
claim 10 to a magnetizing coil for magnetizing
Sensor magnet is directed according to the invention.
Detection of the magnetization according to the invention
bipolar switching sensors are particularly suitable in which the
switch to fields of opposite sign. These sensors
have a switching hysteresis that covers the zero crossing,
the switching state of the sensor remains at the fall of the field to a
even received small field value of opposite sign.
Another advantage of this magnetization is that for magnetization
the permanent magnets used relatively simple coils are used
there fields in the order of magnitude
the saturation fields
be required only in the region of the pole transitions Magnetisierpuls. The power conductors
so that the entire pole area does not necessarily enclose.
magnetic preferred direction of the magnetic material can be in either
Moving direction or perpendicular to the direction of movement. Such
Sensor magnets can
also be formed multi-track and as part of a switching unit
be used in combination with a bipolar magnetic field sensor.
Magnetizing coil for magnetizing such sensor magnets
also stands out
especially in that the
Current conductor of the magnetizing coil, the Polbereiche not completely and
especially beneficial for both
the magnetization as well
the sampling of such sensor magnets has been found when the
Magnetization of the sensor magnet within the wider switching ranges
between the pole transitions
less than 60% of the absolute magnetization decreases near the pole junctions.
The magnetization can be in the middle of the wider switching ranges
almost disappear and go back below 10% of the saturation magnetization.
Sensor magnets can
advantageously as a rotor magnet with frontal magnetization
or as a rotor magnet with magnetization on the outer circumference
be educated. Deviating configurations come according to
Use and purpose as well in question.
The invention will be apparent from the accompanying schematic drawings
explained in more detail. In
show the drawing
1 a conventionally magnetized sensor magnet with four opposing poles of different widths and the induction measured above, as well as the resulting switching states of a bipolar sensor with the corresponding switching thresholds,
2 a sensor magnet magnetized according to the invention, in which the pole transitions were generated by three individual conductors,
3 the magnetization in a sensor magnet having anisotropic orientation in the direction of displacement, with the same magnetization as in 2 in which the sensitivity of the sampled signal to interference fields is reduced,
4 a corresponding sensor magnet to 2 and 3 in the preferred direction perpendicular to the surface, whereby the switching sharpness and accuracy is positively influenced,
5 the current path between current input and current output of a coil for 7-track recording of a digital pattern for the rotational position detection of a disk in the case of an end-side scanning,
6 one with the coil of 5 magnetically magnetized rotor magnet and
7 a magnetized on the periphery rotomagnet with associated bipolar switching sensors that can be configured as a Hall sensor, field plate or GMR sensor.
In the 1 to 4 shown sensor magnets 1 have magnetization patterns with at least two different width switching ranges 1a . 1b between the pole transitions 2 on one or more tracks for field generation for sampling in conjunction with a bipolar switching sensor.
At the sensor magnet 1 from 1 It is a conventional magnetized magnet with four poles 3 opposite polarity 4 , being about the four poles 3 the magnetic flux density "B" is plotted in conjunction with the level "a" for turning ON a bipolar switch and the level "b" for turning OFF such a bipolar switch. The resulting ON or OFF switching states are shown above, and it is particularly noticeable that the ON and OFF switching points E and A are opposite the zero crossing at the pole junctions 2 between the different wide switching ranges 1a . 1b with opposite polarity 4 with an amount X A or X E are shifted relatively strong.
The size of the shift X A and X E depends inter alia on the measuring distance, so that even with exact magnetization, the switching points E and A between the poles 3 shifted from their ideal position. The same problem occurs in multi-track magnetizations in which the poles of the neighboring tracks shift the zero crossing over a track.
To the shift at the pole transitions 2 As low as possible, therefore, according to the embodiments of the invention 2 to 4 every switching range 1a . 1b of the sensor magnet 1 in the middle between the pole crossings 2 a greatly reduced magnetization, so that the Magnetization in the area of pole transitions 2 is highest and reverses as quickly as possible in the direction.
It has proved to be particularly advantageous for the highest possible switching accuracy if the magnetization of the sensor magnet 1 within the wider switching ranges 1b between the pole transitions 2 to less than 60% of the absolute magnetization near the pole junctions.
The magnetization can also be in the middle of the wider switching ranges 1b almost disappear and go back below 10% of the saturation magnetization.
Such conditions are in the magnetized according to the invention sensor magnet of 2 to 4 given.
At the sensor magnet 1 from 2 became the pole crossings 2 with the magnetization directions shown there 4a generated by three individual conductors. The magnetic flux density "B" lies in the middle part between the pole junctions 2 just above the zero crossing between the two levels "a" and "b" for the ON and OFF switching of a bipolar switch and only increases in the immediate vicinity of the pole transitions 2 on the relevant level, so that the ON and OFF switching points E and A of the bipolar switch always in a consistently small distance X a , X e , with respect to the Polübergängen 2 are shifted.
In the embodiment of 3 are practically the same conditions as in the sensor magnet 1 from 2 before, except that in this second sensor magnet 1 the magnetic preferred direction of the magnetic material is in the direction of movement and has an anisotropic orientation in the direction of displacement. The sensitivity of the sampled signal to interference fields is thereby reduced.
Also in this type of magnetization, the magnetic flux density "B" moves in the middle part of the different width switching ranges 1a . 1b in the immediate vicinity of the zero crossing between levels "a" and "b" for turning ON and OFF a bipolar switch to close at the highly magnetized pole junctions 2 suddenly rise and reverse as quickly as possible in the direction, which is a very small shift of the switching points E and A of the bipolar switch against the pole transitions 2 entails.
This also applies to the in 4 shown third magnetization of such a sensor magnet 1 with different wide switching ranges 1a . 1b and a very small magnetization in the middle part between the pole junctions 2 , This sensor magnet 1 has a magnetization of the magnetic material in the preferred direction 4c perpendicular to the direction of movement in the immediate vicinity of the pole transitions 2 , As a result, the switching sharpness and accuracy of a bipolar switching sensor, such as a Hall sensor, a field plate, a GMR sensor or the like, also positively influenced, such as the course of the magnetic flux density "B" in 4 and the above curve for the switching points ON and OFF or E and A of such a switch or sensor can be seen. Such sensor magnets may be multi-tracked.
In 5 is the power path 5 between power input 5a and current output 5b a coil 6 for the seven-track recording of a digital pattern for the rotational position detection of a disk in frontal scanning shown. The winding of the coil 6 is arranged so that in the frontal magnetization of a rotor magnet 10 , as in 6 shown, an alternating succession of NORTH and SOUTH poles N and S results, the tightly packed in the outer part immediately adjacent to each other and increase towards the center in size and decrease in number accordingly, so that finally only in the middle part two NORD- and two SOUTH poles N and S diametrically opposite each other and offset by 180 ° to each other, wherein at all NORD and SÜD poles of different widths each of the middle part between the pole junctions magnetized very low and the magnetization in the pole junctions is highest and there, as in the embodiments of 2 to 4 shown, reversed as quickly as possible in the direction. For better clarity are in the rotor magnet 10 from 6 the NORTH and SOUTH poles N and S are complete only in the upper right quadrant and only partially in the remaining quadrants.
This type of magnetization on such a rotor magnet with frontal magnetization is in 7 in one opposite 6 shown enlarged view. The dash-dot line indicates this 7a each the edge region of the maximum flux density at the NORD poles and the dashed line 7b the range of maximum flux density at the SOUTH poles. The current conductors of the magnetizing coil of 5 are arranged for this kind of magnetization so that they do not completely and tightly enclose the pole regions N and S on the disk-shaped or cylindrical sensor magnet to be magnetized. This can be easily determined by the representation of the magnetizing coil 6 from 5 with the rotor magnet 10 from 6 is brought to cover.
In the further embodiment of 8th it is a magnetized on the outer circumference rotor magnet 11 with with a plurality of switching areas of different widths and these associated bipolar switching sensors 12 , which can be designed either as a Hall sensor, field plate, GMR sensor or similar.
Again, the NORTH and SOUTH poles have a similar sequence and different widths as in the front-side magnetization of the rotor magnet 10 from 7 , The dash-dotted lines 7a show the regions of maximum magnetic flux density of the NORD poles at the pole junctions and the dashed lines 7b the area of the maximum flux density of the south poles in each case in the immediate vicinity of Polübergänge.
In addition to the magnetized on the outer circumference sensor magnet 1 There are several bipolar switching magnetic field sensors 12 for scanning the different width switching ranges of the sensor magnet with the greatly reduced magnetization in the middle of each switching range between the edge magnetizations 7a . 7b , which is highest in the area of the pole transitions and thus only in very narrow, narrow areas and reverses there as quickly as possible in the direction. The magnetic field sensors 12 can, as already mentioned above, each optionally Hall sensors, field plates, GMR sensors or similar components.
- sensor magnet
- switching range
- switching range
- pole transitions
- magnetization direction
- current path
- current input
- current output
the maximum flux density
at the NORD Poland
the maximum flux density
at the SOUTH Poland
- rotor magnet
- rotor magnet
Magnetic field sensors
Turning ON a bipolar switch
Turning off a bipolar scaler
- ON switching point
- OFF switching point
- X A
a shift of the OFF switching point
- X E
a shift of the ON switching point
- North Pole
- South Pole