Apparatus for distinguishing between opposed directions of relative motion of a part having magnetic variations

In the embodiments disclosed in the specification, an apparatus for distinguishing between opposed directions of motion of a part having spaced magnetic variations contains an inductive magnetic sensor disposed adjacent to the path of motion of the variations and having portions with different magnetic couplings with the magnetic variations spaced in the direction of motion of the part.

BACKGROUND OF THE INVENTION 
This invention relates to devices for distinguishing between opposed 
directions of motion of a part. 
Heretofore, devices for distinguishing between opposite directions of 
motion of a part have included sensors displaced from each other in the 
direction of motion of the part, and they require a relatively large 
expenditure, particularly since their positioning depends upon the 
distance between optical or magnetic variations in the part. 
German Offenlegungsschrift No. 3 134 020 discloses an apparatus for 
determining the speed and direction of rotation of a shaft which has a 
rotor of soft magnetic material with a plurality of radially directed 
poles disposed at different angular spacings and a stator with two 
oppositely energized excitation coils and a detecting coil. The apparatus 
is arranged so that the two excitation coils induce oppositely directed 
voltage signals in the detecting coil, and the direction and speed of 
rotation of the shaft are determined from the time sequence and direction 
of the detected voltage signals. This apparatus is costly, not only in 
terms of structural expense and space required, i.e., several coils on one 
stator, some with outside excitation, but also in terms of manufacturing 
cost because of the complicated rotor structure. 
An optoelectronic motion-detecting device disclosed in German 
Offenlegungsschrift No. 3 709 182 is intended only to distinguish between 
two directions of motion of an element which are at an angle of less than 
180.degree.. That device has a slit and a diaphragm partially occluding 
the slit disposed between a source of light and two photodetectors, the 
slit and the diaphragm being arranged so that, upon motion of the element 
in one direction with slit edges oblique relative to that direction of 
motion, the size of slit intervals extending along both edges changes in 
the same sense, whereas upon motion of the element in a direction 
perpendicular thereto the size of the slit intervals changes in opposed 
senses. The signals produced by these changes are processed to obtain 
direction-of-motion signals. 
Finally, German Offenlegungsschrift No. 3 113 538 discloses a device for 
identifying the direction of motion of a vehicle by providing magnetic 
induction loops. In that device, the absolute values of the rising and 
falling slopes of a nonsymmetric signal generated by an induction loop of 
magnetically asymmetrical, for example triangular, configuration are taken 
as a criterion for identifying the direction of motion. That disclosure 
deals with a special case, i.e., an arrangement for road traffic control 
and, moreover, it utilizes a very specific technology, i.e., induction 
loops which generate nonsymmetric signals, thereby requiring an active 
electromagnetic system. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide an 
arrangement for distinguishing opposed directions of motion which 
overcomes the above-mentioned disadvantages of the prior art. 
Another object of the invention is to provide a motion-direction detector 
utilizing passive magnetic induction sensors which is simpler in 
construction and less expensive than prior art devices using such sensors. 
These and other objects of the invention are attained by providing a moving 
part having an element with magnetic variations and an inductive sensor 
adjacent to the path of motion of the variations which has different 
responses to magnetic coupling with the magnetic variations depending on 
the direction of motion of the part with respect to the sensor. The term 
"motion" here refers to relative motion between the part and the sensor, 
which need not necessarily be stationary. 
A special advantage of the invention is that a conventional sensor of 
proven effectiveness of the type widely used, for example, to determine 
the speed or crank angle of an internal combustion engine, is sufficient. 
According to the invention, such a conventional sensor is used in a novel 
way, for example, by oblique placement thereof or with a special form of 
pole shoe, i.e., the face area of an armature of the sensor, so that the 
voltages induced by the magnetic variations of the part upon relative 
linear motion or rotation will have different amplitudes according to 
direction of motion or rotation. As a result, a processing circuit which 
responds to the signals may also be of very simple construction.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring first to FIG. 1, which illustrates a prior art arrangement, an 
inductive sensor 1 is positioned so that its centerline 2 extends radially 
with respect to the center 3 of a gear 4 which is the moving part. The 
gear 4 has peripheral teeth 5 which constitute periodically active 
magnetic variations as the gear rotates. The motion of the teeth 5 beneath 
and past the inductive sensor 1 induces voltage pulses in the sensor, 
whose shape and sequence are independent of the direction of rotation of 
the gear 4. Hence, with this arrangement no information is available from 
the sensor as to the direction of rotation of the gear 4. 
At this point it should be noted that the same result will be obtained if 
the gear 4 is replaced by a part having magnetic variations which moves 
linearly rather than rotationally. 
Considering now a first representative embodiment of the invention as 
illustrated in FIG. 2 by way of example, a sensor 20 is of the same type 
shown in FIG. 1, but it is positioned with its centerline 21 extending 
obliquely to the adjacent portion of a rotating gear 22 as seen from the 
side so that the centerline 21 does not pass through the axis of the gear 
22. As with the gear shown in FIG. 1, the gear teeth 24, which constitute 
magnetic variations, have symmetric shapes in the directions of motion in 
this embodiment. Because of the oblique disposition of the centerline 21 
of the inductive sensor 20, and hence of the armature 25 of the sensor, 
however, a more gradual approach of each of the magnetic variations 24 to 
the armature 25 takes place upon rotary motion of the gear in the 
clockwise direction than during rotary motion in the counterclockwise 
direction. Thus, the armature 25 of the sensor has regions which are 
displaced from each other in the direction of motion of the magnetic 
variations 24 that exhibit different couplings with the magnetic 
variations. This results in different amplitudes of the voltages induced 
in the sensor 20 so that, using an appropriate processing circuit, for 
example in the nature of an amplitude discriminator, the direction of 
rotation of the gear 22 can be determined. 
Another embodiment of the invention is also illustrated by way of example 
in FIG. 2. In this case, the gear has a tooth 26 constituting a magnetic 
variation with a crest surface 27 that is oblique to the direction of 
motion. Thus, the tooth height on the right side, as seen in FIG. 2, is 
less than the tooth height at the left side. In this case, since the 
voltage variations induced in the sensor 20 are produced by the oblique 
setting of the crest surface 27 of the magnetic variation 26, the 
centerline 21 of the sensor may be oriented in the conventional manner 
shown in FIG. 1 so that it lies on the radius 28 of the gear 22. It will 
be understood, of course, that several such teeth providing asymmetric 
magnetic variations may be included in this embodiment of the invention. 
In a further modification of the embodiment shown by way of example in FIG. 
2, the sensor may be disposed so that its centerline coincides with the 
radius 28 as in FIG. 1, but the face of the armature or pole shoe 25 of 
the sensor is oriented at an angle other than 90.degree. to the centerline 
21 so that the pole shoe 25 maintains an oblique arrangement such as shown 
in FIG. 2. 
In the arrangement shown in FIG. 3, an inductive sensor 30 having an 
armature or pole plate 31 is aligned with the radius 32 of a gear 33. The 
gear 33 has a series of identical peripheral teeth 34 constituting 
magnetic variations which move beneath the armature 31 as the gear 
rotates. In this embodiment, as shown in FIG. 4, the armature 31 has 
regions spaced from each other in the direction of motion of the gear with 
different dimensions in the direction transverse to the direction of 
motion. Thus, a first boundary edge 35 of the armature, at the right as 
viewed in FIG. 4, is perpendicular to the plane of motion, whereas a 
second boundary edge 36, at the left as seen in FIG. 4, is oblique to the 
plane of gear motion so that the dimension of the armature parallel to the 
edge 35 decreases toward the left side of the armature. This arrangement 
produces different amplitudes of induced voltages depending on the 
direction of motion of the gear. 
The same result is obtained if the directional asymmetries are produced by 
an oblique tooth profile on the leading or trailing side of each tooth. In 
that case, only one armature edge will be parallel to the tooth flanks as 
seen in plan view. 
The same effect can also be obtained if the cross-sectional shapes of the 
teeth 34 providing the magnetic variations are chosen with suitable 
asymmetry rather than the cross-sectional shape of the armature 31. As a 
rule, however, both in terms of manufacturing outlay and load-transmitting 
functions of the teeth 34, it is more expedient to provide an armature of 
varying dimensions. 
In the graphical representations shown in FIGS. 5 and 6, still by way of 
example, the voltage U induced in the sensor 30 as a function of the time 
t during rotations of the gear 33 in the clockwise direction is 
illustrated in FIG. 5 and in the counterclockwise direction is illustrated 
in FIG. 6. During the clockwise rotation, the positive voltage amplitude 
is limited to the value U.sub.1, whereas during counterclockwise rotation 
of the gear 33, a positive voltage amplitude U.sub.2, considerably greater 
than the amplitude U.sub.1, is produced. The difference between these two 
peak values may be utilized mensurationally as a criterion to indicate the 
prevailing direction of rotation or, in more general terms, direction of 
motion, in the manner described hereinafter. 
FIG. 7 illustrates an inductive sensor arranged according to the invention 
adjacent to magnetic variations such as the teeth, here not shown, of a 
moving part such as a gear. The output signals a from the sensor, which 
may be supplied by way of a signal line 71 to a tachometer (not shown), 
behave as a function of time in the manner again indicated by the curve 
designated a in FIG. 8, assuming clockwise gear motion as shown in FIG. 5. 
In the processing circuit of FIG. 7, the signals are supplied by way of an 
operation amplifier 70' for signal decoupling to two peak memories 72 and 
73 for storing positive and negative peak signals respectively, which are 
so designed that their output signals b and c decay with a given time 
constant. The behavior of these output signals as a function of time is 
also illustrated in FIG. 8. Both of the signals b and c are supplied to an 
addition stage 74, producing an output signal d which is positive or 
negative according to the prevailing direction of motion or rotation of 
the gear 33. In the assumed clockwise direction of motion, on which FIG. 5 
was also based, the sum signal d will be positive. The prevailing sign of 
the sum signal d is evaluated, or determined, in a comparator 75, which 
supplies an appropriate direction-of-motion signal e to a display device 
or the like (not shown). 
In the case of passive inductive sensors, uncertainties may arise because 
they produce usable output signals only when the speed of motion or 
rotation is above a certain minimum value. Hence, it may be expedient to 
distinguish not only between two cases, namely the two directions of 
motion, but to consider a third case as well, in which the direction of 
motion is not indicated with certainty because the linear or rotational 
speed is too low for a definite signal acquisition in the sensor. In 
principle, this distinction can readily be made with the aid of the 
computer, if the absolute value of the speed is also determined. In terms 
of hardware, the distinction can be obtained by a modification of the 
evaluating circuitry shown in FIG. 7 which is illustrated in FIG. 9. 
The modified portion of the processing circuit of FIG. 9 commences with the 
addition stage 74 shown in FIG. 7. Instead of the single comparator 75 
used in FIG. 7, two comparators 76 and 77 are provided, to which threshold 
values or comparison potentials +S and -S having the same absolute value 
but different sign are supplied. One of the comparators 76 and 77, 
depending on the sign of the signal d, will deliver an output signal 
e.sub.1 or e.sub.2, respectively, only when the sum signal d is at least 
equal in absolute value to the quantity S. Consequently, the signal 
e.sub.1 or e.sub.2 represents an unambiguous indication of the prevailing 
direction of motion. If neither of the comparators 76 and 77 delivers an 
output signal, the direction of motion or rotation is indeterminate. 
The sensor signals may alternatively be evaluated digitally. An embodiment 
exemplifying a digital evaluation system will now be explained with 
reference to FIGS. 10 and 11. In FIG. 10, an inductive sensor 101 produces 
signals a in response to magnetic variations which are supplied both by 
way of a line 102 to a rotational speed sensor and to a threshold 
discriminator 103 which is the first component of the processing circuit. 
The sensor output signals a are shown plotted against time in FIG. 11. In 
this case, as in FIG. 8, it is assumed that the direction of motion or 
rotation is the same as that on which FIG. 5 is based. For the opposite 
direction of motion, the graph of FIG. 6 would apply. 
A comparison of the curves in FIGS. 5 and 6 shows that not only are the 
amplitudes different, but the duration of the positive and negative 
intervals of the signals also differ. The processing circuit of FIG. 10 
utilizes this fact by digitizing the signals a from the sensor 101 in the 
signal discriminator 103 so that square wave signals a' are formed as 
shown in FIG. 11. A duration ratio discriminator 104 determines whether 
the duration ratio of the square wave signals a' is greater than or less 
than 0.5. This is a criterion establishing which of the two mutually 
opposed directions of motion the part in question is taking, such as the 
direction of motion of the gear assumed in this case. 
The ratio discriminator 104 may contain two conventional pulse counters, 
each of which determines one of the times t.sub.1 and t.sub.2. Both 
counters operate a flip-flop that is set if, at the end of t.sub.2, the 
quantity t.sub.2 &gt;t.sub.1, and reset if at the end of time t.sub.1, the 
quantity t.sub.1 &gt;t.sub.2. The output signal e of the flip-flop then 
indicates the direction of motion. 
It will be understood that still other embodiments of the processing 
circuitry are possible. For example, instead of the two counters 
mentioned, a single forward-backward counter may be employed, which is set 
to zero at the beginning of t.sub.1, counts down during t.sub.1, but 
counts up during t.sub.2, and the status of the counter at the end of 
t.sub.2, i.e., greater or less than zero, is stored in a flip-flop. 
In this digitized processing circuit, it may be expedient to utilize two 
duration ratio discriminators, for example, delivering output signals only 
when the duration ratio of the rectangular signals a' is, for example, 
greater than 0.6 or less than 0.4, analogous to the arrangement shown in 
FIG. 9, in order to achieve more dependable direction-of-motion 
information. 
The invention thus provides a device of very simple construction for 
distinguishing between oppositely-directed linear or rotational motions of 
a part, requiring practically no additional expense in comparison with 
conventional arrangements for determining the speed or position of a 
rotary part. 
Although the invention has been described herein with reference to specific 
embodiments, many modifications and variations therein will readily occur 
to those skilled in the art. Accordingly, all such variations and 
modifications are included within the intended scope of the invention.