Position detector with non-volatile storage for storing position data upon failure of supply voltage

A position detector with data evaluation circuit has at least one sensor which, in dependence on movement by which the position to be monitored alters, supplies electrical output signals to a circuit arrangement which produces there from a digital signal and puts it into intermediate storage until it is transferred to an evaluation unit. The digital signal reproduces in encoded form the position to be monitored. An energy converter converts a part of the kinetic energy of the movement into electrical energy and an energy storage means stores the electrical energy and provides same for supply to the circuit arrangement. A monitoring circuit outputs a control signal in response to a threatening drop in the supply voltage below a critical limit value. When the control signal occurs the digital signal is written into a non-volatile information storage means, in order thereby to make the position detector independent of an external power supply.

BACKGROUND OF THE INVENTION 
The invention concerns a position detector with data evaluation circuit. 
Position detectors are frequently used as what are referred to as 
intelligent measuring locations, that is to say, in the immediate spatial 
vicinity of one or more sensors generating electrical signals describing a 
movement or position to be monitored, the position detector includes a 
peripheral electronic evaluation and storage means with its own power 
supply, which serves to subject the signals generated by the sensor or 
sensors to a first processing procedure and to put the information 
obtained in that way into intermediate storage until it is called up by a 
user, for example a central measuring and evaluation unit. 
A specific example in that respect is what is referred to as a multi-turn 
circuit in which at least one sensor generates an electrical signal 
whenever a rotatable shaft passes through a preselected angular position. 
The peripheral electronic system derives from those sensor signals a 
counting pulse which, possibly having regard to the direction of rotation 
of the shaft, changes the count value of a counter which is provided in 
the peripheral electronic system. That count value then represents the 
above-mentioned information which is put into intermediate storage and 
which can be called up by a user by way of an interface. 
If the power supply for a peripheral electronic circuit of that kind fails, 
then the information stored therein is lost unless particular measures are 
taken to obviate that. 
Those measures may be for example that the peripheral unit passes its items 
of information quickly to the central unit before its supply voltage has 
fallen to such an extent that data loss occurs. A prerequisite in that 
respect is that the system permits independent transmission of the 
information from the peripheral unit, and the central unit is quickly 
ready to receive the information at the appropriate critical time. Many 
systems fail to meet those requirements. 
A further possibility involves giving the peripheral electronic system its 
own battery arrangement for the purposes of supplying power thereto, which 
batteries are always replaced by new batteries in good time before a 
critical fall in voltage occurs. That requires a high level of monitoring 
and maintenance expenditure which is undesirable and in many cases 
unacceptable. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a position detector which 
is so designed that it is in principle independent of any external power 
supply. 
Another object of the present invention is to provide a position detector 
such that even if an external power supply thereof fails for a long period 
of time the position detector continues to operate satisfactorily, thus 
obviating the need for battery power. 
Still another object of the present invention is to provide a position 
detector responsive to a fall in supply voltage to provide energy 
conversion to maintain operation of the position detector. 
In accordance with the present invention the foregoing and other objects 
are attained by the invention set forth herein. 
As will be seen in greater detail from the following description of 
preferred embodiments of the invention, the present invention involves the 
use of an energy converter which is capable of branching off a part of the 
kinetic energy of the movement to be monitored by the position detector, 
and converting the branched-off part into an electrical current-voltage 
surge which contains sufficient electrical energy to ensure temporary 
power supply for all of the peripheral electronic system so that detection 
and partial processing of a signal which is descriptive of the position to 
be monitored as well as short-term intermediate storage of information are 
guaranteed. 
In that respect the current-voltage surge generated by the energy 
converter, or a part thereof, can be the signal which is descriptive of 
the position to be monitored, or that signal can be generated by a sensor 
which is separate from the energy converter. 
If then that electrical energy which has been supplied by the energy 
converter is suitably stored in an energy storage means contained in the 
peripheral circuit arrangement, it may be entirely adequate to maintain 
for a few seconds the operation of a circuit arrangement which is designed 
to afford a low level of current consumption. 
If the motion to be monitored were to take place continuously at such a 
speed that the energy converter generates the next current-voltage surge 
and fully charges up the energy storage means again, before the supply 
voltage delivered by the latter has fallen too far, that arrangement would 
already be sufficient to attain the object of the present invention. 
As however it is generally not possible to count on that being the case, 
the position detector further has a non-volatile storage means into which 
the information put into intermediate storage in the peripheral circuit 
arrangement is written, before the supply voltage has fallen to such an 
extent that that information is lost in the other circuit units, by means 
of which it is processed in regular operation and put into intermediate 
storage. 
The drop in the supply voltage is monitored by means of a monitoring 
circuit which outputs a control signal for triggering a storage procedure 
when the voltage falls below a critical voltage limit value. 
The underlying realisation of the present invention is thus that, by means 
of a suitable energy converter, for example as is described in detail in 
U.S. Ser. No. 08/352 101 U.S. Pat. No. 5,505,970), it is possible for all 
signal generation, processing and storage procedures, as are required for 
example in the case of a position detector such as a multi-turn circuit 
for ascertaining a coarse measurement value, to be fed from an energy 
component which can be derived from movements, even when they are very 
slow. If the movement comes to a complete halt, the positional information 
last obtained, which is secure in the non-volatile storage means, is not 
in any way altered, and the whole of the peripheral electronic system can 
transfer into a practically current-less and voltage-less rest condition. 
As soon as the movement begins again however and passes through a 
predetermined position, the energy converter again derives sufficient 
kinetic energy to ascertain at least one coarse value which is descriptive 
of the new position, and to store it reliably in the non-volatile storage 
means. 
A certain difficulty arises with that structure out of the fact that the 
most appropriate non-volatile storage means which do not lose the 
information written into them, even in the event of a long-term failure in 
the supply voltage, are EEPRCM-storage means which permit only a limited 
number of writing operations. Admittedly that number is of the order of 
magnitude of same 100,000, but that would result in an unacceptably short 
operating life, if for example 100 writing operations had to be regularly 
carried out per second. 
In order to avoid this problem, the frequency of the writing operations 
must be reduced as far as possible. For that purpose, the attempt is made 
on the one hand to charge the maximum amount of electrical energy into the 
energy storage means for each current-voltage surge, and on the other hand 
to use the stored energy as economically as possible by virtue of the 
choice of energy-saving circuits and components. Here however limits are 
very rapidly reached, particularly when the energy converter is required 
to be of a small size, so that at most it is possible to provide that, as 
already mentioned above, a current-voltage surge supplies energy for an 
operating period of a few seconds. If then, because of a correspondingly 
high speed in respect of the movement to be monitored, the current-voltage 
surges occur with such a density in respect of time that there is no 
threat of the supply voltage falling below the critical value, no storage 
procedures are required. If, in the reverse case, the intervals of time 
between the current-voltage surges and thus the phases of activity of the 
peripheral circuit arrangement are very great, a storage operation must 
admittedly be executed at the end of each such phase, but the number of 
storage operations per unit of time is still also small and a long 
operating life is not seriously endangered. 
What is critical in contrast is a creeping or crawling movement in which 
the current-voltage surges occur with intervals of time which are slightly 
longer than the periods of time for which the energy which can be obtained 
from a current-voltage surge and stored can maintain regular operation. In 
that case, a writing operation must be performed in each case just before 
the next current-voltage surge, and if that happens every few seconds over 
long periods of time, then without further steps being taken, the 
operating life of the EEPRCM-storage means can be very quickly exhausted. 
In order to provide a remedy in this respect, a further development of the 
present invention provides as a first step that a check is made by means 
of a suitable logic circuit prior to the execution of a writing operation 
for each individual storage cell to ascertain whether the logic value 
which is to be freshly written in (`1` or `0`) is or is not equal to the 
stored value, a writing operation for the storage cell in question then 
being effected only when those two values are different. 
If it is assumed that the logic values at the parallel outputs of a pure 
binary counter are to be written into the storage cells, a writing 
operation is therefore required for the cell which has to store the least 
significant bit, in the event of a threat of voltage loss, only when an 
odd number of counting pulses has occurred since the last writing 
operation. Therefore, the service life of the storage means is doubled in 
all the situations of use in which the probability of an even number of 
counting pulses occurring between two voltage failures is equal to the 
probability of the occurrence of an odd number. 
Even if a marked increase in the length of the operating life can already 
be achieved in that way, there is still nonetheless the fact that, without 
additional measures being provided, the storage cells which are used for 
storage of the less significant bits are loaded by writing pulses more 
frequently than the storage cells for the more significant bits, the logic 
value of which changes substantially less frequently. 
As storage means of the kind here in question however became inoperable 
when the most frequently loaded cell has passed beyond the maximum 
permissible number of writing operations, the present invention provides 
further measures for arriving at equidistribution which is as good as 
possible in respect of the writing operations to all the storage cells 
involved. 
Those measures can provide that, after a predeterminable number of writing 
operations, the values of the storage cells are interchanged 
systematically, preferably cyclically. 
A further possible configuration in this respect involves the provision of 
more writable storage cells than the counter whose counter condition is to 
be stored has parallel outputs, so that there is always a group of storage 
cells that remains unused. In this case also interchange can take place 
after a predeterminable number of writing operations so that previously 
unused storage cells are gradually brought into use and storage cells 
which have already been heavily used are shut down. 
A third option in this respect involves supplying the storage means with 
the counter condition in an encoded form such that in regard to the mean 
in respect of time for the storage cells there is an approximately equally 
frequent change between logic `1` and logic `0`. 
In order to arrive at a particularly long service life for the storage 
means, the above-mentioned arrangements may be adopted not just 
alternatively but also in conjunction with each other. 
The consequence of the two arrangements last discussed above is that the 
counter condition which is contained in the respective counter in the 
event of a threat of voltage loss is written into the associated storage 
means in a modified form of representation, that modification being 
effected by means of an encoder. If then sufficient supply voltage is 
available again, the above-mentioned modification in the form of 
representation must be reversed before the counter condition stored in the 
storage means is written back. For that purpose the arrangement includes a 
decoder which operates on the basis of the same code as the 
above-mentioned encoder. 
A further measure for increasing the length of the service life provides 
that a writing operation is not effected immediately upon any noticeable 
drop in the supply voltage. For that purpose, the arrangement operates 
with a supply voltage source, for example a capacitor, which under normal 
conditions supplies a substantially higher voltage than is required to 
maintain regular operation of the counter. Before that voltage has fallen 
to a predetermined fraction, for example 50%, of its regular value, a 
writing operation is triggered off. That has the advantage on the one hand 
that sufficient voltage is always available to be able to execute the 
writing operation in its entirety before data loss occurs. On the other 
hand, a time delay is indirectly provided, which, in all cases in which 
the voltage supply assumes its old value again before the expiry of the 
delay time, prevents any writing operation from taking place at all. That 
is of great significance in particular when the operating circumstances 
are likely to involve voltage failures which admittedly occur frequently 
but generally only last for a short period of time. 
The above-described time delay can be afforded either by means of an 
oscillator with a counter connected on the output side thereof, or by 
means of a comparator for comparing the supply voltage which is actually 
present to a reference voltage. 
Further objects, features and advantages of the present invention will be 
apparent from the following description of preferred embodiments thereof.

DESCRIPTION OF PREFERRED EMBODIMENTS 
Referring firstly to FIG. 1, the position detector shown therein is based 
on the principle described in above-mentioned U.S. Ser. No. 08/352 101 
(U.S. Pat. No. 5,505,970), and the shaft even when the shaft 1 is 
performing extremely slow rotary movements, of outputting a damped 
oscillation signal which can be converted into a counting pulse, when the 
shaft 1 passes through a predetermined angular position. In that situation 
the above-mentioned oscillation signals always contain sufficient energy 
to supply a down stream disposed electronic evaluation system of suitable 
configuration with an adequate amount of electrical energy so that the 
electronic evaluation system can then also perform a counting operation 
and store the freshly obtained count value if otherwise no other supply 
source for electrical energy is available or if the regular electrical 
energy source has failed. 
For that purpose a permanent magnet 3 is non-rotatably connected to the 
shaft 1 and is so oriented that its magnetic poles face radially 
outwardly. Furthermore the position detector illustrated in FIG. 1 has an 
energy converter 5 having an intermediate portion 8 with a permanent 
magnet 9 non-rotatably connected to a shaft 10 which is rotatable about an 
axis that is parallel to the axis of the shaft 1. 
The permanent magnet 9 is also so oriented that the line connecting its 
poles extends radially with respect to the shaft 10. The spacing between 
the shafts 1 and 10 and the radial lengths of the magnets 3 end 9 are such 
that the radial end faces of the magnets 3 and 9 can move closely past 
each other. 
Looking at the radius which extends from the axis of the shaft 1 and on 
which the axis of the shaft 10 is disposed, arranged still further 
outwardly is an E-shaped soft-iron core 11 which is so arranged that the 
three limbs 12, 13 and 14 of its E-shape are oriented inwardly towards the 
shaft 1, preferably in mutually parallel relationship. The middle limb 13 
is disposed precisely on the above-mentioned radius while the to outer 
limbs 12 and 14 are disposed a few degrees of angle in front of and behind 
the middle limb 13 respectively, as considered in the direction of 
rotation of the shaft 10. The spacing of the E-shaped core 11 from the 
shaft 10 is such that the end faces of the poles of the permanent magnet 
9, when it rotates about the axis of the shaft 10, can move at a small 
spacing past the radially inwardly facing end face of the middle limb 13. 
There must be a larger spacing relative to the outer limbs 12 and 14 so 
that the permanent magnet 9 which in principle is freely rotatable 
preferably occupies a starting position in which it is oriented radially 
towards the axis of the shaft 1 and `clings` to the soft-iron core 11 by 
virtue of the magnetic field which is induced therein by the permanent 
magnet. 
An induction coil 15 is wound on the middle limb 13 of the soft iron core 
11 while the one outer limb 14 carries an auxiliary coil 16. 
A further energy converter 5' is formed by an E-shaped soft-iron core 11' 
which is also arranged in such a way that its limbs 12', 13' and 14' are 
oriented inwardly towards the shaft 1, as was described above in regard to 
the core 11. In FIG. 1 the cores 11 and 11' are disposed in diametrally 
opposite relationship but that is not necessarily the case. It is possible 
to adopt any angular position in which the two arrangements do not 
interfere with each other. 
To explain the mode of operation involved, consideration will first be 
directed to the energy converter 5. It is assumed in this connection that 
the permanent magnet 3 which is non-rotatably connected to the shaft 1, 
upon a movement of the shaft 1 in the direction indicated by the arrow R, 
has not yet reached the position shown in FIG. 1 but is at a position 
which is before that position and in which its North pole is increasingly 
approaching the North pole of the permanent magnet 9. In spite of the 
increasing repulsion forces between those two poles the permanent magnet 9 
initially remains in its position in which its North pole is directed 
radially inwardly because its South pole remains `clinging` to the iron 
core 11. As the North pole of the permanent magnet 3 further approaches 
the North pole of the permanent magnet 9, then, before the position shown 
in FIG. 1 which actually never occurs as a stable condition is reached, 
the shaft 1 reaches an angular position in which the repulsion forces 
between those two North poles become greater than the attraction forces 
between the permanent magnet 9 and the soft-iron core 11. 
At that moment the permanent magnet 9 is strongly accelerated for a rotary 
movement in the direction indicated by the arrow S. Shortly after leaving 
the radially oriented starting position, not only the repulsion forces 
between the North pole of the permanent magnet 9 and the North pole of the 
permanent magnet 3 but also the attraction forces between the South pole 
of the permanent magnet 9 and the North pole of the permanent magnet 3 
take effect. By virtue of that double force action, the permanent magnet 9 
has reached a very high speed of rotation when its North pole reaches the 
core 11 of the induction coil 15 and moves past same. 
The result of this is that the magnetic flux from the permanent magnet 9 
firstly passes into the iron core 11 through the outwardly disposed limb 
12 of the iron core 11 and then passes out of the iron core again 
essentially through the middle limb 13. The magnetic flux direction which 
is predetermined in that situation is abruptly reversed when the end face 
of the permanent magnet 9, which is towards the core 11, has travelled 
over the short arcuate distance between the outwardly disposed limb 12 and 
the middle limb 13. That produces a very high value of d.phi./dt, which 
for example generates a positive voltage pulse at the outputs of the 
induction coil 15. When the end face of the permanent magnet 9 then 
travels over the further short arcuate distance between the middle limb 13 
and the other outwardly disposed limb 14 of the core 11, the magnetic flux 
direction in the core 11 reverses again so that now a negative voltage 
pulse of almost the same magnitude is induced. 
When the end face of the permanent magnet 9 moves past the outer limb 14 of 
the core 11, a voltage pulse or surge is also induced in the auxiliary 
coil 16 which is wound on the limb 14. That voltage surge is at least 
sufficient to supply a signal for the electronic evaluation system. The 
moment at which that signal occurs, prior to or after the current-voltage 
surge in the induction coil 15, makes it possible to detect the direction 
of rotation of the permanent magnet 9 and therewith also the direction in 
which the shaft 1 rotated. 
A to-and-fro swinging or oscillating movements of one of the ends of the 
magnet 9 in front of the limbs of the core 11 can also be detected in that 
way. 
As soon as the induction coil 15 has outputted sufficient electrical energy 
to provide for signal evaluation and energy storage, its outputs can be 
short-circuited by the transistor indicated at 17 in FIG. 2, or connected 
together with a comparatively low resistance. In that way, the rotary 
movement of the permanent magnet 9, which otherwise would last for a 
prolonged period of time, is so strongly damped that its North pole moves 
only a short distance past the end face of the core 11, which faces 
towards it, in order then for the North pole of the permanent magnet 9 to 
move back into a position which is turned through 180.degree. relative to 
the position shown in FIG. 1. 
An important consideration here is that the above-described fast rotary 
movement of the permanent magnet 9 is substantially independent of the 
speed at which the shaft 1 and the permanent magnet 3 connected thereto 
move towards the predeterminable angular position, insofar as it does not 
fall below a minimun value. This therefore involves an energy converter 
which, even at extremely slow rotary movements of the shaft 1, takes a 
part of its kinetic energy and converts it into a current-voltage surge or 
pulse of comparatively high power, which not only supplies the electronic 
evaluation system with a signal for counting the revolutions of the shaft 
but also delivers an electrical energy supply which guarantees operation 
thereof for a certain period of time. 
When the shaft 1 rotates through a further 180.degree. in the direction 
indicated by the arrow R beyond the position shown in FIG. 1, the South 
pole of the permanent magnet 3 moves towards the South pole of the 
permanent magnet 9, which is now facing radially inwardly. If that rotary 
movement is continued, the same energy conversion procedure as has just 
been described above takes place. The only difference is that the voltage 
pulses induced in the induction coils 15 and 16 are of opposite signs. 
The energy converter 5' does not have the intermediate portion 8. 
Therefore, when the shaft 1 is rotating very slowly, only weak 
current-voltage surges are induced in the coils 15' and 16' which are 
wound on the core 11', and those surges are generally not suitable as 
means for supplying energy for the electronic evaluation system. 
However the situation is somewhat different when the shaft 1 is rotating 
very quickly. In that case it is possible that the permanent magnet 9 of 
the intermediate portion 8 may no longer be able to follow the movement of 
the shaft 1 and may possibly be almost stationary. In that case however 
the permanent magnet 3 moves past the soft-iron core 11' at such a high 
speed that a sufficiently high value of d.phi./dt is generated in the 
coils 15', 16' and the current-voltage surges outputted by those coils are 
comparable to those described above in respect of the coils 15 and 16, and 
can be used in the same manner. 
Looking now at FIG. 2, reference numeral 19 therein denotes the input stage 
of a circuit arrangement indicated generally at 20 for an electronic 
revolution counter, the input stage 19 including the two induction coils 
15 and 15' of the position detector shown in FIG. 1. 
One end of each coil 15 and 15' is connected to ground while the respective 
other end is connected on the one hand by way of a line 21, 21' to a 
measuring and regulating circuit 24 and on the other hand to two diodes 
26, 27 and 26', 27' which respectively form full-wave rectifiers 28, 28'. 
The positive outputs of the two rectifiers 28, 28' are connected to each 
other and by way of a line 25 to an energy storage means 29 formed by a 
capacitor 30, a line 31 to a voltage monitoring circuit 32, and a line 33 
which includes a decoupling diode 41, to the positive input 34 of a 
capacitor arrangement 35. 
The negative outputs of the rectifiers 28, 28' are also connected to each 
other and connected by way of a line 37 to the negative input 36 of the 
capacitor arrangement 35. 
The side of the voltage supply capacitor 30 which is connected to the 
positive outputs of the rectifiers 28, 28' is connected to all 
corresponding supply voltage terminals of the circuit arrangements shown 
in FIG. 2, as is symbolically indicated by the connecting point +V. The 
lines which extend from sane to the circuit units have been omitted for 
the sake of enhanced clarity of the drawing. 
As already mentioned above, disposed in parallel with the induction coil 15 
is a transistor 17, by means of which the rotary movement of the permanent 
magnet 9 shown in FIG. 1 can be braked. The control signals required for 
that purpose are supplied to the transistor 17 from the measuring and 
regulating circuit 24 by way of the line 47. 
The auxiliary coils 16 and 16' shown in FIG. 1 are not shown in FIG. 2, 
once again for the sake of enhanced clarity of the drawing. In actual fact 
however one end of the windings of each thereof is connected to system 
ground while the other end of their windings is connected to the measuring 
and regulating circuit 24 by way of a line corresponding to the lines 21, 
21'. 
In addition, two lines 38, 39 go from the measuring and regulating circuit 
24 to a main counter 40 for counting the revolutions of the shaft 1 shown 
in FIG. 1. In that arrangement the line 38 which is connected to the clock 
input of the main counter 40 serves to transmit counting pulses, of which 
the measuring and regulating circuit 24 generates one for example whenever 
the permanent magnet 3 connected to the shaft 1 reaches an angular 
position in which it causes the permanent magnet 9, in the above-described 
manner, to rotate rapidly through 180.degree. out of its rest position and 
in so doing generate in the coil 15 a current-voltage surge which 
comprises at least a positive and a negative half-wave. That oscillation 
signal is fed by way of the line 21 to the measuring and regulating 
circuit 24 which derives therefrom a counting pulse for the main counter 
40. 
On the basis of the sequence in which the above-mentioned oscillation 
signals occur at the induction coils 15, 16 and 15', 16' respectively, the 
measuring and regulating circuit 24 also forms a direction signal which is 
passed by way of the line 39 to the main counter 40 and causes the counter 
to increase or reduce its counter condition by a value of `1` whenever a 
counting pulse occurs on the line 38. 
Such a configuration of the counter 40 is employed for example when a 
coarse measurement value in respect of the position of a carriage or slide 
of a machine tool or the like is to be obtained from the number of 
revolutions performed by the shaft 1, as in such situations it is 
important to detect the direction of rotation of the shaft 1. If on the 
other hand the situation only involves ascertaining the absolute number of 
revolutions performed by the shaft 1, in order for example to provide for 
monitoring the operating life or period of service of a component, the 
auxiliary coils 16 and 16' shown in FIG. 1 and the line 39 in FIG. 2 can 
be omitted and the main counter 40 can be in the form of a simple 
incrementing counter. 
In any case the main counter 40 is so designed that it loses the counter 
condition contained therein when its supply voltage falls below a lower 
limit value. In order nonetheless not to lose the information which is 
afforded by that counter condition and in order to have that information 
available when a sufficient supply voltage is restored, the circuit 
arrangement 20 includes a main information storage means 42 which is in 
the form of an EEPROM and which does not lose an item of information 
contained therein even when it is not supplied with operating voltage for 
a very long period of time and whose parallel inputs are connected to the 
parallel outputs of the main counter 40 by means of multiple lines which 
are symbolically represented in FIG. 2 by wide lines, by way of an encoder 
44, whereby the counter condition in the main counter 40 can still be 
written into the main information storage means 42 in good time if the 
voltage monitoring circuit 32 detects that the supply voltage is suffering 
from a critical fall. 
So that the counter condition contained in the main information storage 
means 42 can be read into the main counter 40 again after restoration of 
an adequate supply voltage, the parallel outputs of the main information 
storage means 42 are connected by means of suitable multiple lines to the 
parallel inputs of the main counter 40, by way of a decoder 45 which 
reverses the modification, performed by the encoder 44, in the mode of 
representation of the counter condition, so that that counter condition is 
then available again in its original from and the main counter can 
continue to count possibly without any delay. 
The circuit arrangement 20 further includes an auxiliary counter 48 which 
is designed as a pure incrementing counter and which, as will be described 
in greater detail hereinafter, increases its counter condition by a value 
of `1` for each writing operating with which a count value contained in 
the main counter 40 is transferred into the main information storage means 
42. 
As the counter condition of the auxiliary counter 48 also has to be 
retained in the event of a critical fall in the supply voltage, an 
auxiliary information storage means 50 which is in the form of an EEPROM 
is arranged on the downstream side of the auxiliary counter 48 in a 
corresponding manner to the main counter 40, in such a way that the 
parallel outputs of the auxiliary counter 48 are connected by way of an 
auxiliary encoder 52 to the parallel inputs of the auxiliary storage means 
50 which also does not lose the information contained therein, over 
prolonged periods of time, even when no operating voltage is applied 
thereto. So that the information contained in the auxiliary information 
storage means 50 can be transmitted back into the auxiliary counter 48 in 
its original form when the supply voltage is restored, the parallel 
outputs of the auxiliary information storage means 50 are connected to the 
parallel inputs of the auxiliary counter 48 by way of an auxiliary decoder 
54 which reverses the modification, effected by the auxiliary coder 48, in 
the mode of representation of the counter condition of the auxiliary 
counter 48. 
Whenever the auxiliary counter 48 has reached a preselected counter 
condition and as a result outputs an overflow signal on the line 55, there 
is a change in the code with which the encoders 44 and 52 modify the form 
of representation of the counter conditions contained in the associated 
counters 40 and 48, and with which the decoders 45 and 54 reverse that 
modification. For that purpose the circuit arrangement 20 includes a code 
generator 56 which outputs a fresh code whenever it receives a 
corresponding con, hand signal from the auxiliary counter 48 by way of the 
line 55. In the simplest situation the code generator 56 is in the form of 
an incrementer which increases its counter condition by a value of `1` 
whenever the auxiliary counter 48 overflows. 
As the code generator 56, like the two counters 40 and 48, is designed in 
the form of a circuit which loses the information stored therein in the 
event of an excessive fall in the supply voltage, the arrangement includes 
a second auxiliary information storage means 58 which is in the form of an 
EEPRCM and whose parallel inputs are connected directly to the parallel 
outputs of the code generator 56 and which, in the event of failure of the 
supply voltage, takes over the code last used and stores it until the 
supply voltage is restored. As that code is stored directly in the mode of 
representation used by the code generator 56, no decoder is required for 
the reverse transfer operation so that the parallel outputs of the second 
auxiliary information storage means 58 can be connected directly to the 
parallel inputs of the code generator 56. 
Control of the writing operations with which the information contained in 
the counters 40 and 48 and the code generator 56 are transferred into the 
main information storage means 42 and the auxiliary information storage 
means 50, 58 respectively, and reverse transfer of those items of 
information out of the storage means 40, 50 and 58 into the counters 40, 
48 and the code generator 56 is effected under the management of a control 
logic means 60 for safeguarding data, which on the one hand receives a 
control signal from the voltage monitoring circuit 32 by way of a line 61 
whenever the supply voltage threatens to fall below a critical value, and 
which on the other hand is connected by way of a command line 63 to the 
`write` inputs of the EEPRCM-storage means 42, 50 and 58, and a command 
line 65 to the `preset` inputs of the main counter 40 and the auxiliary 
counter 48, and a command line 67 to the `preset` input of the code 
generator 56. 
So that the counter condition contained in the main counter 40 can be 
outputted to an external user, the parallel outputs of the main counter 40 
are connected to a corresponding number of inputs of an interface which, 
whenever it receives a corresponding request signal from the user by way 
of the line 71, can for example serially output by way of the line 72 the 
information which is fed thereto in parallel. 
The capacitor arrangement 35 includes two capacitors 74, 75 which are 
fixedly connected together in series and two capacitors 76, 77 which are 
also fixedly connected together in series. The one side of the series 
circuit consisting of the capacitors 74, 75 can be connected by way of a 
controllable switch 80 to the positive input 34 of the capacitor 
arrangement 35 and by way of a further controllable switch 81 to the 
positive output 84 of the capacitor arrangement 35, to which one side of 
the series circuit consisting of the capacitors 76, 77 is also fixedly 
connected. 
The other side of the series circuit 74, 75 is connected by way of a 
controllable switch 86 to the negative input 36 of the capacitor 
arrangement 35, by way of a controllable switch 87 to system ground, and 
by way of a controllable switch 88 to the negative output 90 of the 
capacitor arrangement 35, to which the other side of the series circuit 
consisting of the capacitors 76, 77 is fixedly connected. 
The connecting point between the two capacitors 74, 75 can be connected by 
way of a controllable switch 92 to ground and by way of a controllable 
switch 93 to the connecting point of the two capacitors 76 and 77. Finally 
the positive side of the series circuit 74, 75, which is connected to the 
switches 80, 81, can be connected by way of a controllable switch 94 to 
the negative side of the series circuit 76, 77. 
The switches 80, 81, 86, 87, 88, 92, 93 and 94 are actuated simultaneously 
and jointly by the control logic means 60 in such a way that they can 
adopt two different switching states. In the first switching state which 
is shown in FIG. 2, the switches 80, 81, 86, 88 and 92, 93 are closed 
while the switches 87 and 94 are opened. In the second switching state in 
contrast the switches 80, 81, 86, 88 and 92, 93 are opened and the 
switches 87, 94 are closed. 
The positive output 84 of the capacitor arrangement 35 delivers an 
increased writing voltage for the storage means 42, 50 and 58 while the 
negative output 90 is connected to the voltage monitoring circuit 32. 
Referring now to FIG. 3, the voltage monitoring circuit 32 diagrammatically 
shown therein includes a voltage divider comprising two resistors 95, 96, 
the resistances of which are for example in a ratio of 1:2. If then the 
supply voltage +V is applied to the positive input which is connected to 
the voltage supply capacitor 30 and the voltage -V which is initially of 
the same absolute value is applied to the input which is connected to the 
negative output of the capacitor arrangement 35, the connecting point of 
the resistors 95, 96, which is connected to the positive input of a 
comparator 97, is at a voltage which is V/3 above ground potential and 
becomes equal to 0 when the voltage at the positive input has fallen to 
half the value of the voltage at the negative input. The two resistors 95, 
96 can be of very high resistance so that the comparator arrangement shown 
in FIG. 3 consumes only very little current. By way of the division ratio 
of the voltage divider 95, 96, it is possible to adjust the fraction of 
the voltage at the negative input, below which the voltage at the positive 
input must fall in order to cause the comparator 97 to respond. 
In the description set out hereinafter of the mode of operation of the 
circuits shown in FIGS. 2 and 3, it is assumed that the capacitor 30 is 
the sole voltage supply source of the electronic assembly illustrated, and 
is always charged up to its maximum voltage again by the oscillation 
signals which are induced in the coils 15 and 15' respectively by the 
rotating shaft 1. In consideration of the mode of operation of the energy 
converter 5, which as indicated above is described in detail in 
above-mentioned U.S. Ser. No. 08/352 101 (U.S. Pat. No. 5,505,970), the 
current-voltage surges which are induced in the coils 15, or the 
oscillation signals which include at least one positive and negative 
half-wave, contain sufficient electrical energy for that charging-up 
effect even when the shaft 1 is rotating very slowly. 
For charging up the capacitors 74 through 77, the switches 80, 81, 86, 87, 
88, 92, 93, 94 are in the positions shown in FIG. 2 so that the capacitor 
30 and the capacitors 74 and 76 are charged up to a voltage +V by the 
positive half-wave and the capacitors 75, 77 are charged up to the 
approximately equal voltage -V by the negative half-wave. Accordingly, the 
voltage 2V which is composed of the values +V and -V related to ground is 
dropped across the capacitor series circuits 74, 75 and 76, 77 
respectively. With an energy converter which operates on the basis of the 
principle described with reference to FIG. 1, it is possible to achieve a 
maximum charging voltage for the capacitor 30, which is approximately 
twice as high as the critical limit V.sub.min, below which the counters 40 
and 48 and the code generator 50 threaten to lose the information stored 
therein. 
As the capacitor 30 serves as a current supply source for the illustrated 
circuit units, after each charging operation the voltage which is dropped 
thereat continuously falls until the next charging operation while the 
voltages at the capacitors 74 and 76 which are decoupled by the diode 41 
and the capacitors 75, 77 remain practically unaltered as all those 
capacitors are non-loaded during the switching condition shown in FIG. 2. 
Therefore as long as the shaft 1 is rotating at a sufficient speed or 
moves to and fro about a position in which the energy converter 5 is 
repeatedly subjected to pulse operation, the current supply for the entire 
circuit arrangement is safeguarded by the continual recharging of the 
capacitor 30 so that the main counter 40 can count the pulses which the 
measuring and regulating circuit 24 derives from the oscillation signals 
supplied by the induction coils 15, 16 and 15', 16' respectively and 
transmits to the main counter 40 by way of the line 38, having regard to 
the directional information which arrives by way of the line 39. If the 
external user feeds a request signal to the interface 70 by way of the 
line 71, the counter condition which the main counter 40 has respectively 
attained can be readily read out by way of the line 72. Storage of the 
counter condition contained in the main counter 40, in the main 
information storage means 42, does not occur as long as the voltage 
available at the voltage supply capacitor 30 does not fall below the value 
established by the ratio of the resistances of the resistors 95 and 96 as 
indicated in FIG. 3 of the voltage monitoring circuit 32. 
If however the time interval between two successive oscillation signals in 
the coils 15 and 15' becomes so long that the supply voltage falls below 
the above-mentioned limit value, the comparator 97 of the voltage 
monitoring circuit 32 outputs a corresponding information signal to the 
control logic means 60 by way of the line 61. The control logic means 60 
first opens the switches 80, 81, 92, 93, 86 and 88 and closes the switches 
87 and 94 so that the voltage available thereto from the positive output 
84 of the capacitor arrangement 35 assumes the value of +4V relative to 
ground. That quadrupled voltage is certain to be sufficient to be able to 
perform the three writing operations which are simultaneously caused to 
occur by the control logic means 60, by way of the line 63. In that 
situation the counter conditions of the main counter 40 and the auxiliary 
counter 48 as wall as the code contained in the code generator 56 are also 
written into the associated EEPRCM-storage means 42, 50 and 58 before the 
supply voltage has fallen to such an extent that the information contained 
in the counters 40, 48 and in the code generator 56 is lost. 
The capacitor arrangement 35 which is not loaded by the regular current 
consumption of the circuit arrangement 20 therefore performs two functions 
here. It primarily serves as a writing energy storage means to ensure that 
adequate energy is always available if, just before a critical voltage 
drop, the information to be rescued has to be long-lastingly stored. In 
addition thereto it can advantageously be used as a reference voltage 
source which makes it possible to detect a critical fall in the supply 
voltage. 
In situations in which the shaft 1 can move over long periods of time at a 
speed of rotation at which the current-voltage surges which charge the 
capacitor occur precisely with such a time interval therebetween that the 
supply voltage falls in a critical manner, the writing operations which 
are involved in that situation, involving writing into the EEPRCM-storage 
means 42, 50 may occur at a frequency such that, without additional 
measures being taken, the service life of the overall arrangement would be 
excessively curtailed as EEPROM-storage means are admittedly capable of 
maintaining information stored therein, without any change, over very long 
periods of time, even in the absence of a supply voltage, but they permit 
only a limited number of writing operations. 
As a first step towards countering that problem, it is provided that a 
logic circuit indicated by a broken dividing line is disposed at the 
parallel inputs of each storage means 42, 50 and 58. The logic circuit may 
comprise for example a plurality of EXCLUSIVE-OR circuits with inverted 
output, each of which checks, for the associated storage cell, whether the 
binary value which is to be freshly written in is different from the 
binary value which is already stored therein, and by means of an AND-gate 
enables a writing operation only when that condition is met. 
Since, as will be described in greater detail hereinafter, the code 
generator 56 changes the code that it delivers only after a large number 
of writing operations, the above-described measure is completely 
sufficient to guarantee a long service or operating life for the storage 
means 58. 
In regard to the main counter 40 which counts each full revolution of the 
shaft 1 and the auxiliary counter 48 which increases its counter condition 
by the value `1` in each writing operation, at least the positions with 
the lower values or significances change their logic value very 
frequently, so that it is to be reckoned that the value to be stored is 
frequently different from the stored value. 
In order nonetheless to permit a large number of writing operations to be 
performed and thus to achieve a long service life for the overall 
arrangement, the counter conditions contained in the counters 40 end 48 
are not written directly in parallel into the storage means 42 and 50. On 
the contrary, interposed in each case is a respective encoder 44 and 52 
which, under the control of the code generator 56, performs at least one 
but preferably both of the following functions: 
1. The encoders 44 end 52 can be used to interchange the values or 
significances of the storage positions in the storage means 42 and 50, 
preferably in a cyclic manner, whenever the decoder 56 outputs a fresh 
code, that is to say when the counter 48 has counted a predetermined 
number of writing operations and has therefore outputted a corresponding 
control signal at its overflow output 55, so that for example the storage 
position with the previously lowest significance becomes the storage 
position with the highest significance and all other storage positions on 
the significance scale move by one step downwardly or vice-versa. This, in 
conjunction with the feature that a writing operation takes place only in 
those storage positions whose content differs from the value which is to 
be freshly written into the storage means, provides that all storage 
positions are approximately equally frequently written into. 
2. Alternatively or in addition thereto, it can be provided that at least 
the auxiliary storage means 50 has more storage positions which are to be 
written in parallel, than the counter 48 has parallel outputs. In that 
case the encoder 52 can be used to modify the selection of the storage 
cells used for the storage procedure, out of the total available number of 
storage cells, in depended on the code generated by the code generator 56, 
whenever a given number of writing operations has taken place. Thus it can 
be provided for example that, when ten storage cells are required for 
storage of the information contained in the counter 48, the storage means 
50 has twenty such storage positions, of which cells 1 through 10 are used 
during a first series of storage operations and cells 2 through 11 are 
used during a second series of storage operations, and so forth, until 
finally all twenty storage positions present have been used and have been 
subjected to the loading of an approximately equal number of writing 
operations. In addition thereto the first storage means 42 may also have a 
number of storage positions that is larger than the number required for 
storage of the counter condition of the counter 40. In that case the 
change in selection of the respective storage positions used is effected 
in a corresponding manner by means of the encoder 44. 
As already mentioned the measures set forth above in 1. and 2. can be 
employed individually or both together, in which respect a particularly 
long service life can be attained in the latter case. 
When the count values contained in the counters 40 and 48 are written into 
the storage means 42 and 50 in the mode of representation after 
modification by the encoders 44 and 52, a further drop in the supply 
voltage is harmless because the EEPRCM-storage means 42, 50 and 58 are 
readily capable of maintaining the information stored therein, even over 
long periods of time when there is no supply voltage. 
When the induction coil 15 supplies a new current-voltage surge so that a 
sufficiently high supply voltage is again available for the circuit shown 
in FIG. 2, the control logic means 60 first passes a control pulse on the 
line 67 to the preset input of the code generator 56 which thereupon 
receives the code stored in the storage means 58 and applies it to the 
encoders 44 and 52 and the decoders 45 and 54. The control logic means 60 
next passes a command pulse on the line 65 to the preset inputs of the 
counters 40 and 48 which thereupon take over the counter conditions which 
occur at their parallel inputs and which are identical to the counter 
conditions existing prior to the voltage failure and which are also in the 
correct mode of representation as the modification in the mode of 
representation which was effected in the preceding writing operation by 
the encoders 44 and 52 to prolong the service life of the storage means 42 
and 50 has been reversed again by the decoders 45 and 54. It is only when 
that reverse transfer procedure is terminated that the count value of the 
storage means 48 is increased by `1`, whereby the writing operation 
effected prior to the voltage loss is counted. That `belated` counting 
operation is required so that, in the situations in which that counting 
operation results in overflow of the storage means 48 and thus a 
modification in the cede outputted by the code generator 56, the operation 
of returning to the counters 40 and 48 the counter conditions stored in 
the storage means 42 and 50 is conducted using the same code as that 
employed in the preceding writing operation. 
That therefore ensures that the count values existing prior to the voltage 
loss are written unchanged into the counters 40 and 48 and those counters 
can continue to count in the proper fashion, starting from that basis. By 
virtue of making the charging voltage of the voltage supply capacitor 30 
substantially greater than the critical voltage, being the lower voltage 
limit value at which the control logic means 60 triggers off a writing 
operation, a delay time is afforded in the sense that a writing operation 
does not have to be performed immediately upon any minor drop in the 
supply voltage. As in many situations of use the occurrence of stoppage 
times which are shorter than the above-mentioned delay time is more 
probable than the occurrence of stoppage times which are longer, the 
number of writing operations required is considerably reduced. That means 
that the service life of the storage means 40, 50 and 58 is 
correspondingly increased. 
Instead of the comparator shown in FIG. 3, the voltage monitoring circuit 
32 can use a timing member, for example an oscillator with an oscillation 
counter disposed on the output side thereof, in which case the reset input 
of that counter receives the pulses outputted by the measuring and 
regulating circuit 24 shown in FIG. 2, by way of a line 99 shown by a 
broken line in FIG. 2. As a charging operation for the capacitor 30 
immediately preceeds each of those pulses, it is possible by means of the 
above-mentioned oscillator-counter assembly to define a period of time 
during which it can be assumed with certainty that an adequate supply 
voltage is available and no writing operation has to be performed. It is 
only when the counter which counts off the oscillations of the oscillator 
exceeds a predetermined count value that a suitable command signal is 
passed to the control logic means 60 by way of the line 61. However it 
will be noted that the current consumption of such an oscillator-counter 
assembly is higher than that of the high-resistance voltage divider 95, 96 
and the comparator 97, and it is not possible to make use of the maximum 
period of time. 
Another embodiment is of such a configuration that the energy converters 5 
and 5' which are shown in FIG. 1 are only used to ensure a supply of 
electrical energy to the circuit arrangement shown in FIG. 2 at low or 
high speeds of rotation of the shaft 1, while the information about the 
revolutions of the shaft is obtained by means of an additional capacitive 
rotary sensor which consumes only very little electrical energy. That 
rotary sensor is then connected directly to the measuring and regulating 
circuit 24 which evaluates the signals supplied thereby, and outputs a 
counting pulse on the line 38 whenever a preselected angular position is 
detected by the rotary sensor. As the output signals of such a rotary 
sensor, which is of a known configuration, also permit detection of the 
direction of movement, the measuring and regulating circuit 24 can also 
derive from such signals the directional signal which is to be outputted 
on the line 39. 
It will be noted that it is also possible to adopt design configurations in 
which only the energy converters 5 shown in FIG. 1, in which the auxiliary 
coils 16 and 16' have to be omitted for example for reasons of space, are 
used in conjunction with one of the above-mentioned capacitive rotary 
sensors. In that case the current-voltage surges outputted by the energy 
converters can be used both for charging the capacitor 30 and also for 
deriving a counting pulse in the above-described manner, while the 
information in respect of direction of movement is obtained by means of 
the signals of the capacitive rotary sensor which, in all situations in 
which the rotary movement of the shaft 1 does not take place in an 
extremely slow creep mode, makes it possible to conclude, by virtue of the 
fact that it delivers an absolute angular value of between 0.degree. and 
360.degree., whether the pulse last delivered by one of the energy 
converters was generated by the shaft 1 and therewith the permanent magnet 
3 having rotated in the clockwise direction or in the counter-clockwise 
direction. 
Although it has been initially assumed in the foregoing description that 
the capacitor 30 represents the sole power supply source for the circuit 
arrangement 20 illustrated in FIG. 2, that however is not necessarily the 
case. It is certainly possible to provide an external voltage/current 
source which is in parallel with the capacitor 30 and which generally 
supplies the circuit units with electrical energy. All the above-described 
operating procedures occur in that case when that external voltage/current 
source is switched off or fails for any reason. If that failure occurs 
when the shaft 1 is stationary, the voltage monitoring circuit again 
detects the potentially harmful drop in the supply voltage and causes the 
control logic means 60 to perform a writing operation, in the manner 
described hereinbefore. If then the shaft 1 is rotating while the external 
voltage supply has failed, an oscillation signal is generated whenever one 
of the ends of the permanent magnet 3 passes one of the energy converters 
5 or 5', in the above-described manner. The signal produced not only 
supplies a counting pulse but also sufficient electrical energy to count 
that counting pulse and to store it in the non-volatile storage means 42 
if the voltage falls further. 
If in contrast the oscillation signals which are produced by a rotary 
movement of the shaft 1 occur with a sufficiently high frequency because 
the shaft 1 is rotating sufficiently rapidly, the supply of energy is 
guaranteed without interruption by the capacitor 30 and the main counter 
40 can count the revolutions of the shaft 1 without a writing operation 
having to be performed on each occasion. 
Those two modes of operation can be continued until the main power supply 
is working again and an uninterrupted supply of power for the circuit 
arrangement is guaranteed even when the shaft is rotating very slowly. 
It has already been mentioned that it is advantageous, as an alternative or 
in addition to the measures described in detail hereinbefore, for the 
counter condition of the respective counter to be fed to the parallel 
inputs of the associated storage means in a form which is encoded in such 
a way that a change between logic `1` and logic `0` or vice-versa occurs 
for the maximum number of storage positions with a better equidistribution 
in respect of time and thus for the storage cells which are otherwise most 
heavily loaded, occurs considerably less frequently than is the case when 
using a pure binary cede. 
That will be illustrated hereinbefore by reference to the example of a 
2-bit binary counter. If the counter counts four pulses, starting from a 
counter condition of zero, then the following logic states occur in 
accordance with the regular binary code at its outputs A.sub.1 and A.sub.2 
: 
______________________________________ 
Counted pulse Output A.sub.1 
Output A.sub.2 
______________________________________ 
0 0 0 
1 1 0 
2 0 1 
3 1 1 
4 0 0 
______________________________________ 
Therefore a change in the logic value occurs four times at the output 
A.sub.1 but only twice at the output A.sub.2. This, in conjunction with 
the step of providing that a writing operation is operative only at the 
storage cells in respect of which the logic value which is to be freshly 
written into same is different from the value that is already stored, 
results in a loading which is twice as high on the storage cell associated 
with the output A.sub.1. 
If however the logic states fed to the storage means are encoded in the 
following manner: 
______________________________________ 
Counted pulse Output A.sub.1 ' 
Output A.sub.2 ' 
______________________________________ 
0 0 0 
1 1 0 
2 1 1 
3 0 1 
4 0 0 
______________________________________ 
then a change in value for each storage cell occurs with equal frequency 
and the cell associated with the output A.sub.1 ' is loaded only half as 
severely, and that affords twice the service life length. 
A corresponding consideration can also be demonstrated in relation to 
counters with a larger counting capacity. 
It will be appreciated that the above-described structures according to the 
invention have been set forth solely by way of example and illustration of 
the principles thereof and that various modifications and alterations may 
be made therein without thereby departing from the spirit and scope of the 
invention. 
It will further be noted at this point that the reference numerals 
contained in the appended claims serve for ease of interpretation thereof 
and are not intended to have restrictive effect.