CA1297979C - Procedure and means for producing a contrast image - Google Patents
Procedure and means for producing a contrast imageInfo
- Publication number
- CA1297979C CA1297979C CA000508515A CA508515A CA1297979C CA 1297979 C CA1297979 C CA 1297979C CA 000508515 A CA000508515 A CA 000508515A CA 508515 A CA508515 A CA 508515A CA 1297979 C CA1297979 C CA 1297979C
- Authority
- CA
- Canada
- Prior art keywords
- image
- image forming
- frequency
- current
- points
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
Abstract
ABSTRACT OF THE DISCLOSURE
A procedure and an apparatus for producing an image based on contract discrimination in an image forming apparatus with one-dimensional or multi-dimensional image field employable in small format image forming applications, have image signals obtained from each image forming points producing an electric current in a respective image forming channel, this current exerting an influence on the current passing from a tapping point of the image forming channel to said channel, and on the voltage produced at the tapping point, in such a way that their product is proportional to the image signal current, and the output of image forming is a frequency which is proportional to the current, a desired contrast heightening being achieved by supplying externally a suitable current to an interaction network connecting the tapping points of one or more image forming channels by suitably selected impedances, and the frequencies obtained from each image forming channel constituting the starting point for the image forming cycle.
A procedure and an apparatus for producing an image based on contract discrimination in an image forming apparatus with one-dimensional or multi-dimensional image field employable in small format image forming applications, have image signals obtained from each image forming points producing an electric current in a respective image forming channel, this current exerting an influence on the current passing from a tapping point of the image forming channel to said channel, and on the voltage produced at the tapping point, in such a way that their product is proportional to the image signal current, and the output of image forming is a frequency which is proportional to the current, a desired contrast heightening being achieved by supplying externally a suitable current to an interaction network connecting the tapping points of one or more image forming channels by suitably selected impedances, and the frequencies obtained from each image forming channel constituting the starting point for the image forming cycle.
Description
~L2~7~7~
The present invention concerns a procedure and an apparatus for producing an image based on contrast discrimination in an image forming means with one-dimensi.onal or multi-dimensional image fie].d.
A plurality of industria]. products and Eunctions would be easy to automate and their efficiency cou]d be increased if a simple image forming means serving as a visual or tactile sense were available for diverse control and monitoring functions. Activities of this kind wou]d 10 be, for instance, optimizing the operation of lift doors or location finding among the she].f beams in a warehouse system in automated materia]. handling.
Among the image Eorming means in current use, the means worki.ng wi.th a great number oE image e]ements 15 are not suitable for use in smal.]. format controlling and monitoring tasks. For instance, coding a colour TV image in rea]. time re~uires an approximate].y 85 Mbit/sec handling rate, whereas the clock frequency of a fairly fast 8-bit microprocessor is no more than 6-8 M~lz. The 20 design of the present i.nvention i.s intended Eor sma].].
format systems with a relative].y sma].l number of image points, and it is concentrated on pre-processing the image information, which in this case can be carried out large].y independent of the app].icati.on objects.
Sma].l format monitoring systems which do not use a camera or equiva].ent means are as a ru].e bul].t around a sma].l number of independently operating on/oEE .sensors.
The most common sensor types are the photoce].l, supersonic sensors and induckive and capacitive sensors. Such 30 sensors have been developed to be more accurate and ].es.s expensive, whereby it has been possible to :Lncrease their number in various applicationsr but in those app].ications such sensors sti].l operate individually, each with its own operating point setting. A design di.ffering in the 35 synchronizing oE different points of measurement cou].d be a proximity detector with six image forming points. In such a design, the signals from capacitive antennas wou].d , .. .... -. .. .. . . .. . . . .
97~3i7~
have been processed in combination, whereby an adequate change of capacitance at any one antenna produces a distinguishable change with reEerence to the mean change of all antennas.
The advantage of such a six-point design in comparison with one-point sensor applications and di~ferentially operating two-point sensor applications is its more extensive range oE coverage. Since the outputs of the antennas are merely compared with their mean, this 10 cannot yet be considered to represent any versatile image forming. D~awbacks of such a si~-point design are, furthermore, its high sensitivity to background capacitances in the environment, which particu].arly in lift applications changes from floor to floor, and poor 15 control in special situations, for instance particu].arly when the lift doors are close to their extreme positions.
For instance, regarding the sensi.tivity of the edge sensors on a lift door compro~ises are Erequent.l.y unavoidable owing to environmental conditions, since 20 otherwise an unreliable, over-sensitive means wou].d be the result.
An image composed o~ as few as six points contains much more information than a mere deviation of mean. Means hand].ing typically greater numbers of image 25 points, such as photodiode arrays, have been so constructed that a].l .image formi.ng points have as nearly as possible the same gain. I:E it is desired to compose an image based on a plura].ity of inexperls:ive sensors, e.g.
phototransistors, the variatlon oE gains and soiling and 30 other environmental factors impede any attempt at stable synchronization of the .image formi.ng poi.nts. Individua].
calibration of the ampliEiers cannot be considered to be a satisfactory solution in such cases, even though a microcomputer for instance can automatical].y attend to 35 t~lis.
The object oE the present inventi.on i.s to provide an image forming procedure and means for small format viewing applications and in which -the drawbacks . ~, g mentioned have been eliminated or decisively reduced, and the implementation of which is simple, insensitive to variation~ of conditions and to disturb~nce~ and, moreover, inexpensive.
The present invention provides a procedure for producing an image based on contrast discrimination in an image forming means with a one-dimensional or a multi-dimenslonal image field, wherein image signals obtained Erom image Eorming points produce an electric current in an image forming channel connected to each o.E the image forming point~, the current afEecting the current flowing from the tapping point of the image forming channel to the channel, and the voltage established at the tapping point, in such a manner that their product is proportional to the image signal current, wherein the output oE image Eorming is a frequency which is proportional to the current, and wherein a de.sired contrast heightening is accomplished by supplying from -the outside a suitable current to an inter -ac-tion network connecting the tapping points oE one or more image forming channels by means o.E suitably selected impedances, the erequencies obtained from each image forming channel con~tituting the starting point Eor the image Eorming phase.
The advantages of a procedure Oe th.is klnd include the :Eact that thanks to the interaction network, the currents caused by the lmage Eorming points "leak" to those po.Lnts where the current is higher than normal owing to an object that has entered in Eront o.E the background of the image :Eield. ~rhis .eature i.s the basis :Eor contra~t discrimination, because the di.EEerences between image ;Eorming channels are heightened and the sensitivity improves.
Ba~ed on Erequency, it is easy to trans.Eorm the image into dig:ital Eorm, eOg. by counting the number oE
pulses over a constant period of time. The contrast image deEined by the frequency components can be after-processed in a way appropriate in each particular application.
Another signiEicant advantage is then that the image ~9~9~7~
signals can be modified in real time in parallel by simple -tools, directly into digital Eorm.
In one advantageous embodiment oE the procedure of the invention, by means oE series- connected resistor-capacitor impedances in the interaction network there isproduced a frequency component which is proportional to the angular changes of the intensity image formed by the original image signals, and which in the course oE a time determined by the changes adapts the permanent changes of the viewed object, contributing to the production of a smooth image.
In another advantageous embodiment of the procedure of the invention, to the tapping points of the image forming channels there is connected a resistance of which one end is connected to a suitably selected voltage level, by which is produced a frequency component proportional to the absolute value of the image signals.
~daptivi-ty is generally understood to mean that the reaction of a certain member to a disturbance diminishes until the reaction has entirely ceased to exist although the disturbance is still present. Features oE this kind have been built into various controlLing means even before. They have been encumbered by the drawback that even major disturbances, such as a person, become adapted out of the monitor image although the cause oE di,sturbance is still present and should be taken into account. The procedure oE the invention operates in three diEEerent ways in a cAse like thls: by adaptatlon oE a component proportionaL to the second derivate, that i~, to the changes in ~lope of a curve Eormed oE the intensity signals Erom the image Eorming points; by creatlng and maintaining a component proportional to the absolute values while the dlsturbance i~ present; by an "aEter-image efEect" of the adaptation when the disturbance disappears, thereby producing a "negative" image in the adapted smooth background image. Said diEferent modes oE
operation aEord a chance to design intelligent monitoring means appllcations.
~2~9~
The fact that the first frequency image component, which in normal situations is the decisive Eactor, is proportional only to the second clerivate o:E the object of image orming implies that indication o~
disturbance will not occur Eor changes taking place all over the image field, not even iE their magnitude were to change linearly across the image field: the disturbance indication only observes discontinuous, local changes. In this manner, any irrelevant changes in the environment are filtered out of the image forming.
In a further advantageous embodiment oE the procedure of the invention in the field of lift technology the capacitive image forming system based on contrast discrimination is emp1.oyed in one-dimensional :Eorm on the lift's sa.Eety edge 80 that at least on one side oE the liEt door opening are provided image ~Eorming points in a vertical line to monitor the entrance oE people and things in the opening of the li.Et door, and that when the image forming system concludes that an obstacle has entered between the liEt doors it transmits inEormation to this eEfect to the control system of the li:Et.
'l'he term "safety edge" has its origin in the mechanical saEety means on lift doors which consist Oe spring-loaded strips countersunk in the door edges and which on hitting an obstacle act on the limit .switches controlling the operation o.E the liEt door. The observation can be made, reEerring to the above-mentioned characteristics of the invention, that the saEety edge oE
the invention has adecluate sensitivity in all circumstances by the aid oE the .Eiltering out oE
environment variables and by adaptation, in addition to which it present~ good stability, thanks to its simple , . construction.
In a liEt embodiment o.E the procedure o~ the invention the image Eorminc3 means monitors the operat.ion of the liEt doors independently by observing the absolute values of the capacitances seen by the antennas in the door openings, and the duration oE obstacle indication, ~2~9'7~
whereby the ~afety edge is made inactive while the doors are clo~ed, in which case the capacitance i~5 clearly higher than while the doors are open, or when the .sum o:E
the durations of obstacle indications exceeds a pre~etermined limit.
Thanks to the operation that has been described, the degree o~ availability of the lift is maximally independent oE sa~ety edge failures because the safety edge is permanently made inactive by internal monitoring, and substitutes for instance a photocell to serve as saEety mean~s in nearly all instances oE defect.
The invention Eurther provides an image :Eorming apparatus ~or producing an image based on contrast discrimination in a one-dimensional or multi-dlmensional ima~e field having individual image forming points for producing a one-dimenslonal or multi-dimens.ional image based on contrast discrimination, comprising, one image forming channel Eor each image Eorming point, the channels compris.ing signal/frequency converters ~or sensors at the points, the converters comprising two-~tage electric charge pumps having a Eirst stage which is a producer oE a current signal of the image Eorming point, and a second phase which is a Erequency oscillator, the :Erequency which is variable by means oE the current signal, and oE a tapping point between the stages, or an interaction point, to which the tapping o.E one or several other converter~
has been connected over a suitable impedance Eor Eorming an interaction network; and .interpreter menns .Eor interpreting an lmage produced by the channels and composed oE Erequencies.
~ 'he e.lect:ric charge pump is in this connection understood to mean the perlodic charging oE a cap~citance in the :Ereyuency oscillator Oe the converter with an external, constant Erequency voltage, the current caused by this voltage in the second stage oE said voltage being inEluenced b.y the image signal oE the .Eirst stage, and the pace at which said capacitance is being charged determining the output frequency oE the converter.
7~7 In the accompanying drawlngs:-Figure 1 presents the principle oE operation o.E
-the basic unlt of means for implementing the procedure of the invention, Figure 2 shows a circuit diagram of an embodiment oE the basic unit o:E the invention, Figure 3 illustrates the p:ropagation of a signal in the basic unit, Figure 4 presents the principle oE connecting together a p.l,urality of basic units, Figure 5 illustrate.s an example oE contrast .~ heightening as taught by the invention, Figure 6 illustrates examples oE the contrast heightening in diEferent phases, lS Figure 7 shows various forms oE adaptation, Figure 8 present.s the means applying the procedure of the invention, at block diagram levell Figure 9 shows the block 8 oE Figure 8, at circuit diagram level, Figure 10 presents the sensitivity curve of the mean~ oE Figure 9, ~ue to different weighting o:~ the image :Eorming points, in the plane oE the door opening, Figure 11 shows the output signals oE the means o.E Figure 9.
The ba~ic design oE the lnvent;on may be embodied as a two-stage s,ystem with input.s and outputs related to each othe.r i.n a certain way. ~y employing pract:ical quantit.ies such as current, voltage and :Erequency ln connection with the input.q and outputs, the de,Einition Oe the sy~tem can be concretized a~ in Figure 1.
~ n input quantity is in the Eorm of a current io, and an output quantity is a .frequency El. A tap is provided at a point where a current il is .introduced and whlch has the voltage Ul. The two-stage operation is realized as shown by the formulae lnscri.bed in the block in such a way that the input quantity current io affects directly only the tap point voltage Ul if the current il is constant. The output fl is directly proportional to the current 11 (with the coe:~icient kl) When the tap is connected by an impedance either to a :Eixed voltage level or to the taps oE circuit operating in parallel, inteeaction is produced between the voltage Ul and the current il, by which the current il, and hence the output frequency fl, will change.
A circuit implementing the formulae given in Figure 1 is presented in Figure 2. An important feature of the circuit is a suitably selected tapping point, by the aid oE which the Eeatures of the basic circuit can be modified by the mutual interaction of the circuits operating in parallel in such a way that a plurallty of practical applications, which may be based on the interaction of a number of signals, ~ind a simple solution, The operation of the circuit depicted in Figure 2 can be described in the :Eollowing way, neglecting the diode threshold voltages and assuming that UO U1 (see Figure 3).
The voltage supply oE CMOS circuits 4,5,6 (e.g.
oE NOT type) is E, and the decision threshold of the circuit i.5 a~sumed to be E/2. The voltage Ul is tllen the diEEerential voltage between the deci3ion threshold and the capacitor C2.
By the aid of the capacitor C2, electric charge is pumped at Erequency fO Erom the capacitor C2 to the capacitor Cl. This produces a current, the average oE
which is io. IE UO U1, we .elnd:-~1.) io = Co*Uo*Eo ~'he voltage oE capacitor Cl at the beginning Oe the cycle is lower by the amount Oe Ul than the deci3ion threstlold E/2. With the current io, the capacitor Cl is charged to the decision threshold in the time:-~2) tl = ~Cl*Ul)/io After the time tl has passed, the capacitor Cl is discharged by the aid of the CMOS circui.ts, delivering the charge:-~Z97~79 g (3) Q = Cl*~, whereaEter it is once again charged through the diodes to a level WtliCh iS lower than the decision threshold by the amount Ul, thus starting a new cycle. In this manner, pulses are produced which have the frequency fl = l/tl.
The current that has been removed is tfrom equation 3~:-(4) Ql/tl = (Cl*E)/tl = il (at equilibrium) Hence, 1 il/(Cl E) = kl+il; kl = l/(Cl*E) that is, one oE the two conditions Eor tlle block oE Figure 1 has been Eound. From equations (2) and (5) we Eind fl = 1/t] = io/(Cl*U1) = il/(Cl*E), with Ul*il = E*io = ko io; ko 15 that i9, the other condition.
Since exact satisEying of the conditions of thefunction blocks requires that no current is introduced in the circuit through the input, the input quantity io has been generated by the aid of the capacitor pump. We may then according to equation (1) as the actual input quantity consider CO~ UO or fO if the other two quantities are kept constant. In the example, voltage and Erequency are constant, and capacitance is the variable input quantity, whereas when using sensors oE other types the output quantity oE the sensor can be converted e.g. into a frequency, applying a technology known in the art. In the example appllcatlon, the current Lo will according to equation (1) remain dependent on the capacitance only:
~6) io = k2 CO
By connecting the variou~ taps oE the basLc circuLts oE
E'igure 2 to each other through diEeerent impedance~ and by arranging suitable current supply points in the irnpedance or interaction network, a circuit Eor efEecting the pre-processlng oE the functionaL lmage inEormation is obtained, which at the same time serves as an analog/digital converter because the output is a frequency, which is directly appropriate to be processed digitally.
~Z~7~75~
In Figure 4 is presented the pre-proces~ing circuit ~or a one-dimensional capacitance image, at block level. To the tapping points oE the diEEerent blocks, the constant current i i~ supplied, and the points are connected with each other e.g. by a resistor ~. The distribution oE the constant currents i between diEferent channels is partly dependent on the voltages Ul..~Un. The frequency of the output El..Ofn oE each channel reElects the capacitances COl...COn oE the input pattern in the way that the frequency image that is obtained is p~incipally proportional to the second deriva-te oE the re~pective capacitance image.
In Figure S this relationship has been illustrated. In Part I there is shown a case in which the level oE the C pattern changes. This causes no changes in the corresponding f pattern. The change of the derivate ~slope) of the C pattern, taking place in Part II, also has no eEfect on the E pattern. Only when the derivate oE the C pattern 2 changes - Part II[ - will the addition to the f pattern of frequency components proportional to thi~ derivate be caused.
In Figures 6a - 6E have been pre~ented the steps in processing the image signal in an apparatu.s comprising slx capacitive antennas disposed to be the image Eorming points oE a one-dimen~ional lmage. It is seen in Figure 6a how the antennas see an object that has appeared adjacent to the third antenna: the capacitance C03 oE the third anterlna increa~es while the va]ues oE the other antennas ~tay substantially unchanged. IE we imagine lines entered between the capacitance value~ oE the antennas, we get a capac;tive image in which the anguLar changes between the point~ contain the inEormation which i8 essential from the point oE view oE the means oE the invention.
In Figure 6b, the charlges oE the capacitances have been allowed to be reflected in the output frequencies El - f6 of the capacitance/Erequency converters of Figure 2, the corresponding frequency image resulting thereErom. It is seen that ttle angular changes have increased compare~l with the capacitance image, that is, the contrast has been lleightened. This ~eature is produced by the aid of the interaction network.
In Figure 6c, the a~ter-processiny phase oE the exemplary apparatus has been reached, in which the Erequency image fl - ~6 that has been produced is converted into time differences between the image Eorming channels by measuring in synchronized manner the frequency image components on the basis oE the passage time diEEerences oE a given predetermined number oE pulses, in the present instance eight pulses. At the same time, ~requency/time conversion takes place.
In Figure 6d is shown how the time image obtained in the measuring phase has been converted by subtracting from each other the time quantities oE
mutually a~jacent points tl - t6, this process resul-ting in ive time diEference guantities tl2, t23, t34, t45 and t56. A procedure of this kind also contributes to higher contrast.
In Figure 6e, one mode oE weighting of the channels is presented, lower weighting factors (Kl, K2) having been assigned to the "marginal channels" compared with the ilnage Eorming points located in the centre Oe the image Eield (K3). rrhis i~ Erequently advantageous Eor the reason that the background Eactors in the marginal areas mayr owing to discontinuity, deviate strongly rom the central area oE the image, while at the ~nme time they are le~s sLgnificant from the point Oe view Oe operation, and thereEore decrea~ing their weighting factor will result in more reLiabl¢ operatlon oE tne apparatu~. The weighting factors are often fixedly set by component selection and component connections, while on tlle other hand the sensitivity a~justment S must be easy to accomplish, in order to optimize the operation.
Figure 6f presents the ultimate image in our exalnple of capacitive isnage processing. In the example, the object that has appeared in the vicinity o the third :
~2~ 7'~
antenna produces in the voltage image a voltage IJ3 which surpasses the decision threshold and thereby forwards indica~ion of the presence oE the ob~ect. The vol-ta~3e~
are produced by integrating, with reference to the digital S signal indicating the termination oE count;ng perEormecl on the ~requency fl - f6 of each channel, the time interval from the end of the counting on its frequency to that taking place in the next channel on a lower frequency, and that when the voltage oE any one channeL obtained in this manner by integrating exceeds the decislon threshold, an indication oE the appearance oE the object in the image fieLd is Eorwarded.
F'igures 7a and 7b illustrate the aclaptivity oE
the apparatus. If, as above, an object appears in front oE the antenna No. 3, the result is a frequency curve as plotted in solid lines in F'igure 7a. Normally, the smooth curve has been disturbed by a frequency rnodification corresponding to the extra capacitance which the object represents, as has been described in the foregoing. If the object which caused the disturbance remains in the image field for some time, the proEile oE the curve starts to flatten in the manner plotted with dotted lines in Figure 7a, until tne curve is once more a horizontal line. ~his phenomerlorl i~ due to the Eact that in the interaction network the connection Erom the image Eoeming channel to the other channels has been establislled by rneans oE
capacitor~, wh-~reby the extra eurrent Erom the neighbourillg channels cau~ecl local:ly by a high anterlna capacLtance wiLL not contlnue aEter tht3 current-pro(lucing voltage dLEEt3rellce~ betwet3n the interaction points have gone over to the capacitors. F'inally, the resuLt in tlle cast3 oE the curve undergoLng adaptation is a smooth Erequerlcy Lmage, even iE the object whictl caused the di~turbance sllould stiLl exist in the viewed object.
By adaptation, the eEEect oE ~lowly changing background disturbances can be reduced. IE the object is removed after the adaptation has taken place, a "hole"
corresponding to the object remains in the image field ~Z~79 seen by the antennas, the result thus being a "negative"
frequency image in which the disturbance constitutes a local minimum of equivalent size. This is useEuL, ~Eor instance, in the lift saEety edge to be described later on, as the door will not close at once aEter an obstacle that has kept the door open for a prolonged time.
Figure 7b presents a non-adaptive colnponent which is proportional to the capacitance value derived Erom the image Eorming points. This component appears and disappears immediately with the object that caused the disturbance. In addition, the relative eEEect oE said component on the ultimate Erequency image has in this case been adjusted to be less than that of the aaapting component, whereby only sizable disturbances produce a signiEicant non-adapting component. This component i~s useEul for the reason that iE, Eor instance, in the case oE a liEt a person keeps the door open, it is necessary that the door monitoring system is aware oE the person being still in the door opening, as otherwise the door would close when the disturbance caused by the person has ultimately faded due to adaptation.
The apparatus oE the invention is described in greater detaiL in the Eollowing by the ald oE an example, reference being made to Figures 8 to 11.
In Figure 8, a capacitive saEety edge to be installed on the llEt doors i~q concerned, the ultimRte Eunction oE which i8 to indLcate whether there is an obstacle in tlle door openLng or not when the door close~.
Currently, this functLon is implemented by mechanical "collisLon strips"~ by photocells or, Eor instance, by capacitive, independently o~erating or dLEEerentially operating sensors.
It is one oE the physicaL Eundamentals oE
capacitance sensing that the basic capacLtance oE the sensor is exclusively dependent on the area and ~hape o~
the antenna. The other capacitances that have to be taken into account in practical antenna constructions are the ~2~3 7~7~
basic capacitance of the circuit, the antenna protection plate capacitances and the disturbance capacitances.
A protection plate placed on one side oE t~le antenna plate reduces the eEEective area oE the antenna approximately to one-halE and prevents the antenna from detecting capacitances in the door structure, whereby the basic capacitance oE the antenna is reduced and its sensitivity improves. The adaptation, voltage protection and placement Eeatures comprised in the apparatus embodying the invention also contribute to higher sensitivity achievable in practice.
IE the door oE a liEt consists oE two halves moving towards each other, it is necessary to have one saEety edge 7 with image processing means 8 Eor each side.
If the door opens altogether on one side, one saEety edge i9 enough. Other equipment entities oE the system are a control rnens 9 and a power source 10. The voltage supply points oE tlle image processing means 8 oscillate in joint Eorm with reEerence to the grounded level, e.g. at 30 kHz requency and at 50 V amplitude (U12 and ~22), by which oscillation t~le pumping efEect oE electric charges is accomplished with tlle antenna capacitances. The voltages oE the cor-nection points oE the circuits 8 have been indicated by Ull and UL2, oE which more below, and reEerence numerals ll and 12 indicate outputs oE the control mean,s g.
In Figure 9 has been presented one circuit dLagram oE the image processing means 8 oE ~'igure 8 wlth its capacitlve antennas 7. I,et us conslder the pha3es ln proce~ing in th~ mean.~ the image signal produced in the second charlrlel Erom the top in the Eigure. It is assumed that the antenna has just registered that an object ha~
appeared in its image Eiel.d, by reglsterlng a dl~turbance ca~acltance.
The circuit block 14, which corresponds to the circuit oE Figure 2, acts as a "pump", which induces a certain immunity to electrical interEerence. In practical applications, this is oE great importance since no special ~:~g~
interference shielding is required and little attention need be p~id to freedom from dlsturbances of the zero level. The energy needed Eor the pumping is obtained Erom the voltage U12, which is a 50 V d.c. voltage pulsed at 30 kllz ~requency. From the volta~e pulses a current i2 passes through the diode D22, and this current "pumps"
charge into the capacitor C21.
When the antenna capacitance increases due to a disturbance capacitance, the current i2 increases in direct proportion thereto, according to Eormula ~1). The voltage corresponding to the voltage U1 of the interaction point P2 in F'igure 2, which was determined to be the voltage between the operating polnt oE the circuit and the interaction point, increases correspondingly. Elereby, the capacltors C22 and C12 supply an extra current component to the chanrlel that was disturbed, for attaining a new voltage at rest at the interaction point P2. rhis extra current supplied to the "disturbance channel" is Eelt not only in the discharging feequency oE the capacitor C21 oE
thi5 channel but al~o in the adjacent channels as a corresponding loss oE energy at their interaction points, resulting in a "negative" reaction in comparison with the disturbed channel. This eEeect can be compareci e.g. with the "]ateral inhibition" observed in bioloyical nerve systems, leading to heightening oE conteast.
After the new equilibrium voltage oE the interaction point P2 has been reached, the Elow oE currellt ceases between channels in the interaction network.
Simultaneous]y, the eEEect oE the disturbance capacitance ends. The disturbance ha~ now become adapted to blend with the backgrouncl image seen by the antenna. IE however a significant disturbance is concerned, which in the present instance would be at least a human hand in the immediate proximity oE the antenna, the increase oE U
causes a small current increase across the resistor R21.
The respective resistors of this and the other channels have been connected to a constant voltage on the terminal 13. The current component obtained Erom the constant voltage source over the resistor R21 does not adapt but Elows as long as the voltage Ul of the interaction point P2 is unchanged. By th,is extra component oE the current il of Figure 2, the non-adaptive Eeature is produced.
All said current components inEluence the discharging frequency of the capacitor C21 through the current i2, said frequency constituting the frequency component f2 oE the channel'in question. The frequency is counted by samples oE eight pulses, synchronou~ly, with octal counters 15, the time difEerences emerging from the count being interpreted as was described in connection with Figures 6c and 6d.
Immediately after the fastest channel tin the present instance that which has the output A2) has counted its eight pulses, the digital signal ~2 indicating termination of count begins to exert influence on the inverter circuit operating at an adjustable voltage level and which supplies current to the integration input 17 of the Erequency/voltage conve,rter 21, whereby the voltage U2 equivalent to the relative Erequency of the ctlannel with reference to the other channels begins to build up across the capacitor C23. The values oE the capacitors C13 - C63 in combination with the resistors R12 - R62 serve at the same time through their RC time constant.s as nnother weighting facility for di,EEerentiating the ~ensitivity oE
the channels.
~ tletl eight pulses oE the channel outputs ~2 - ~5 have been counted, all counters 15 have pulled thelr output up, which ls observed by the down~pull oE the output Oe the gate 16. ~rhls signals the pulse Eorming circuit 18 to deLiver A pu.L8e ~I synchronizing the reading mo~nent, to the disturbance detection gate 20. The same puLse aLso opens the outputs oE the image Eorming circults 14 to start R new Erequency counting cycle. The pulse forming circuit 18 also gives a command to the tumbler 19 to set the counters 15 to zero by a zeroing pulse R.
In a normal case with no disturbance, all inputs oE the disturbance detector 20 are thus at logical zero at ~L2~97~
the moment oE reading, whereby the N~ND gate 20 delivers a pulse to the transistor Tl in the output stage 22, which in turn by pulsing the voltage Ull inEorms the control means (Flgure ~, reEerence numeral 9) that there is no d iB turbance.
In the present instance, the volt~ge U2 surpasses the decision threshold at the moment when a pulse ~l arrives at the disturbance detector 21), which has the eEEect that no pulse is forthcoming Erom the N~ND gate 20. There~ore the pulse oE the output stage 22 also Eails to be eormed.
In Figure 10 has been depicted the coverage constituted by a safety edge with six antennas, the image forming channels having been weighted in the manner presented in the foregoing. The highest sensitivity has been arranged to occur at the image forming points located in the centre of the image Eield, for which points the maximum sensing distance a can be employe~ with the present apparatus, even in adverse conditions (e.g. an unstably moving closely positioned shaft door), depending on the antenna design, to be up to 100 mm.
Finally, in Figure 11 is presented the volt~ge Ull between the connection points oE the bLock 22 containing tl~e output stage, and voltage stabiLlzing circuits, in various situations; the Eunctions caused by its output pul~es in the control means 9 oE Figure 8 and typical voLtage and Ere~luency vaLues. 'rhe voltaye Ull ls adjustable Ln the range l6 - 22 V, by which adju~tment the volt~ge leveL at the point 24 is aEEected, WtliCtl supplies the invertLng circuits controllLng the integration inputs 17. The changeable voltage l.evel aEEect~ the dLsturbance detection sensitivity in the manner illustrated by Figure 6e. In the normal operating mode N, when the liEt door iB
open, pulse~ indicating the end Oe the measuring cycle and freedom Erom disturbances in the door opening occur at Ere~uency 120 - 150 Elz. When the lift doors close, the capacitance oE the antennas increases strongly in the region DC so that the frequency of the pulses increases to ~2~'7~
16 0 - 3 0 0 l-~ z . In a disturbed situat ion D, the pul~e~
cease, as was described above, and the ab~ence oE at least two consecutive pulses is interpreted in the control to be a ~listurbance requiring opening oE the doors.
When a disturbance occurs in tlle region D, the control mean~ 9 of Figu~e 8 pulls its output 11 down aEter a ~elay equivalent to about two missing pulses. The line returns to state 1 after the disturbance has ceased to act.
Wt-en the doors close, the pulse Erequency increases, whereby after a certain delay the control means renders the saEety edge inactive by pullin~ down the output 12~ This must be done because when the antenna capacitances increase stxongly, various disturbances oE
operatlon, difficult to predict, may occur. Since the saEety edges are not needed while the doors are closed, ttley can most appropriately be made inactive. In this case the line S merely indicates that the saEety edges are indeed out oE action. Here too the present apparatus aEfords the advantage that it distinguishes between the increase of the overall capacitance due to closing the doors and ~ disturbance capacitance due to an obstacle in ttle door opening, whereby thls function, too, becomes reLiable. The saEety edge is again made active aEter the doors open, with a certain delay.
IE the disturbance is on Eor longer than 20 secondsl or iE the summed disturbance de~ection time exceeds this ~ame value, the error checking circuLt F'S i~
switched on and it puLl~ the line 12 down. ~y the aid oE
thiC3 output, the unLt controlling the operation oE the door is inEormed that the sclEety edge is not Eurlctiona1, and it is then po.ssible to switch on e.g. a photocell to be the door-opening means.
ThereaEter, if there has been no obstacle or the obstacle ha~3 gone away, the doors are closed, and a check is made to ascertain whether the line S has gone up. If it has, the safety edge is most probably in order, an~
transition is made to the normal mode of operation, to 797~
checking the pulses oE Ull. l~ the image forming means i~
deEective, it is most unlikely that the saEety edge cut-out detector (the line S) is operative, and the saEety edge then remains subjugated to the error checking circuit FS. The error checking circuit may consist of A Eully previously known, simple logic circuit; thereEore, it will not be presented in any greater detail.
It is obvious to a person skilled in the art that diEEerent embodiments of the invention are not exclusively conEined to the example presented in the foregoing but may vary within the scope oE the claims presented below. Eor instance, the image Eorming may be implemented by means of any sensors or component~ suitable for image forming, such as phototransistors, photodiodes, photoresistors, etc. when the output signal produced by the sensors is converted e.g. into frequency. [t is also possible, applying existing techniques, to log-modlllate the signal iE its range of variation is very wide, before supplying it to the contrast image Eorming means oE the invention. ~'he contrast image Eormed by the aid of image point-speciEic Erequencies may also be aEter-processed in a number oE ways, e.g. Eor shape-identifying applications.
~ ~ .
The present invention concerns a procedure and an apparatus for producing an image based on contrast discrimination in an image forming means with one-dimensi.onal or multi-dimensional image fie].d.
A plurality of industria]. products and Eunctions would be easy to automate and their efficiency cou]d be increased if a simple image forming means serving as a visual or tactile sense were available for diverse control and monitoring functions. Activities of this kind wou]d 10 be, for instance, optimizing the operation of lift doors or location finding among the she].f beams in a warehouse system in automated materia]. handling.
Among the image Eorming means in current use, the means worki.ng wi.th a great number oE image e]ements 15 are not suitable for use in smal.]. format controlling and monitoring tasks. For instance, coding a colour TV image in rea]. time re~uires an approximate].y 85 Mbit/sec handling rate, whereas the clock frequency of a fairly fast 8-bit microprocessor is no more than 6-8 M~lz. The 20 design of the present i.nvention i.s intended Eor sma].].
format systems with a relative].y sma].l number of image points, and it is concentrated on pre-processing the image information, which in this case can be carried out large].y independent of the app].icati.on objects.
Sma].l format monitoring systems which do not use a camera or equiva].ent means are as a ru].e bul].t around a sma].l number of independently operating on/oEE .sensors.
The most common sensor types are the photoce].l, supersonic sensors and induckive and capacitive sensors. Such 30 sensors have been developed to be more accurate and ].es.s expensive, whereby it has been possible to :Lncrease their number in various applicationsr but in those app].ications such sensors sti].l operate individually, each with its own operating point setting. A design di.ffering in the 35 synchronizing oE different points of measurement cou].d be a proximity detector with six image forming points. In such a design, the signals from capacitive antennas wou].d , .. .... -. .. .. . . .. . . . .
97~3i7~
have been processed in combination, whereby an adequate change of capacitance at any one antenna produces a distinguishable change with reEerence to the mean change of all antennas.
The advantage of such a six-point design in comparison with one-point sensor applications and di~ferentially operating two-point sensor applications is its more extensive range oE coverage. Since the outputs of the antennas are merely compared with their mean, this 10 cannot yet be considered to represent any versatile image forming. D~awbacks of such a si~-point design are, furthermore, its high sensitivity to background capacitances in the environment, which particu].arly in lift applications changes from floor to floor, and poor 15 control in special situations, for instance particu].arly when the lift doors are close to their extreme positions.
For instance, regarding the sensi.tivity of the edge sensors on a lift door compro~ises are Erequent.l.y unavoidable owing to environmental conditions, since 20 otherwise an unreliable, over-sensitive means wou].d be the result.
An image composed o~ as few as six points contains much more information than a mere deviation of mean. Means hand].ing typically greater numbers of image 25 points, such as photodiode arrays, have been so constructed that a].l .image formi.ng points have as nearly as possible the same gain. I:E it is desired to compose an image based on a plura].ity of inexperls:ive sensors, e.g.
phototransistors, the variatlon oE gains and soiling and 30 other environmental factors impede any attempt at stable synchronization of the .image formi.ng poi.nts. Individua].
calibration of the ampliEiers cannot be considered to be a satisfactory solution in such cases, even though a microcomputer for instance can automatical].y attend to 35 t~lis.
The object oE the present inventi.on i.s to provide an image forming procedure and means for small format viewing applications and in which -the drawbacks . ~, g mentioned have been eliminated or decisively reduced, and the implementation of which is simple, insensitive to variation~ of conditions and to disturb~nce~ and, moreover, inexpensive.
The present invention provides a procedure for producing an image based on contrast discrimination in an image forming means with a one-dimensional or a multi-dimenslonal image field, wherein image signals obtained Erom image Eorming points produce an electric current in an image forming channel connected to each o.E the image forming point~, the current afEecting the current flowing from the tapping point of the image forming channel to the channel, and the voltage established at the tapping point, in such a manner that their product is proportional to the image signal current, wherein the output oE image Eorming is a frequency which is proportional to the current, and wherein a de.sired contrast heightening is accomplished by supplying from -the outside a suitable current to an inter -ac-tion network connecting the tapping points oE one or more image forming channels by means o.E suitably selected impedances, the erequencies obtained from each image forming channel con~tituting the starting point Eor the image Eorming phase.
The advantages of a procedure Oe th.is klnd include the :Eact that thanks to the interaction network, the currents caused by the lmage Eorming points "leak" to those po.Lnts where the current is higher than normal owing to an object that has entered in Eront o.E the background of the image :Eield. ~rhis .eature i.s the basis :Eor contra~t discrimination, because the di.EEerences between image ;Eorming channels are heightened and the sensitivity improves.
Ba~ed on Erequency, it is easy to trans.Eorm the image into dig:ital Eorm, eOg. by counting the number oE
pulses over a constant period of time. The contrast image deEined by the frequency components can be after-processed in a way appropriate in each particular application.
Another signiEicant advantage is then that the image ~9~9~7~
signals can be modified in real time in parallel by simple -tools, directly into digital Eorm.
In one advantageous embodiment oE the procedure of the invention, by means oE series- connected resistor-capacitor impedances in the interaction network there isproduced a frequency component which is proportional to the angular changes of the intensity image formed by the original image signals, and which in the course oE a time determined by the changes adapts the permanent changes of the viewed object, contributing to the production of a smooth image.
In another advantageous embodiment of the procedure of the invention, to the tapping points of the image forming channels there is connected a resistance of which one end is connected to a suitably selected voltage level, by which is produced a frequency component proportional to the absolute value of the image signals.
~daptivi-ty is generally understood to mean that the reaction of a certain member to a disturbance diminishes until the reaction has entirely ceased to exist although the disturbance is still present. Features oE this kind have been built into various controlLing means even before. They have been encumbered by the drawback that even major disturbances, such as a person, become adapted out of the monitor image although the cause oE di,sturbance is still present and should be taken into account. The procedure oE the invention operates in three diEEerent ways in a cAse like thls: by adaptatlon oE a component proportionaL to the second derivate, that i~, to the changes in ~lope of a curve Eormed oE the intensity signals Erom the image Eorming points; by creatlng and maintaining a component proportional to the absolute values while the dlsturbance i~ present; by an "aEter-image efEect" of the adaptation when the disturbance disappears, thereby producing a "negative" image in the adapted smooth background image. Said diEferent modes oE
operation aEord a chance to design intelligent monitoring means appllcations.
~2~9~
The fact that the first frequency image component, which in normal situations is the decisive Eactor, is proportional only to the second clerivate o:E the object of image orming implies that indication o~
disturbance will not occur Eor changes taking place all over the image field, not even iE their magnitude were to change linearly across the image field: the disturbance indication only observes discontinuous, local changes. In this manner, any irrelevant changes in the environment are filtered out of the image forming.
In a further advantageous embodiment oE the procedure of the invention in the field of lift technology the capacitive image forming system based on contrast discrimination is emp1.oyed in one-dimensional :Eorm on the lift's sa.Eety edge 80 that at least on one side oE the liEt door opening are provided image ~Eorming points in a vertical line to monitor the entrance oE people and things in the opening of the li.Et door, and that when the image forming system concludes that an obstacle has entered between the liEt doors it transmits inEormation to this eEfect to the control system of the li:Et.
'l'he term "safety edge" has its origin in the mechanical saEety means on lift doors which consist Oe spring-loaded strips countersunk in the door edges and which on hitting an obstacle act on the limit .switches controlling the operation o.E the liEt door. The observation can be made, reEerring to the above-mentioned characteristics of the invention, that the saEety edge oE
the invention has adecluate sensitivity in all circumstances by the aid oE the .Eiltering out oE
environment variables and by adaptation, in addition to which it present~ good stability, thanks to its simple , . construction.
In a liEt embodiment o.E the procedure o~ the invention the image Eorminc3 means monitors the operat.ion of the liEt doors independently by observing the absolute values of the capacitances seen by the antennas in the door openings, and the duration oE obstacle indication, ~2~9'7~
whereby the ~afety edge is made inactive while the doors are clo~ed, in which case the capacitance i~5 clearly higher than while the doors are open, or when the .sum o:E
the durations of obstacle indications exceeds a pre~etermined limit.
Thanks to the operation that has been described, the degree o~ availability of the lift is maximally independent oE sa~ety edge failures because the safety edge is permanently made inactive by internal monitoring, and substitutes for instance a photocell to serve as saEety mean~s in nearly all instances oE defect.
The invention Eurther provides an image :Eorming apparatus ~or producing an image based on contrast discrimination in a one-dimensional or multi-dlmensional ima~e field having individual image forming points for producing a one-dimenslonal or multi-dimens.ional image based on contrast discrimination, comprising, one image forming channel Eor each image Eorming point, the channels compris.ing signal/frequency converters ~or sensors at the points, the converters comprising two-~tage electric charge pumps having a Eirst stage which is a producer oE a current signal of the image Eorming point, and a second phase which is a Erequency oscillator, the :Erequency which is variable by means oE the current signal, and oE a tapping point between the stages, or an interaction point, to which the tapping o.E one or several other converter~
has been connected over a suitable impedance Eor Eorming an interaction network; and .interpreter menns .Eor interpreting an lmage produced by the channels and composed oE Erequencies.
~ 'he e.lect:ric charge pump is in this connection understood to mean the perlodic charging oE a cap~citance in the :Ereyuency oscillator Oe the converter with an external, constant Erequency voltage, the current caused by this voltage in the second stage oE said voltage being inEluenced b.y the image signal oE the .Eirst stage, and the pace at which said capacitance is being charged determining the output frequency oE the converter.
7~7 In the accompanying drawlngs:-Figure 1 presents the principle oE operation o.E
-the basic unlt of means for implementing the procedure of the invention, Figure 2 shows a circuit diagram of an embodiment oE the basic unit o:E the invention, Figure 3 illustrates the p:ropagation of a signal in the basic unit, Figure 4 presents the principle oE connecting together a p.l,urality of basic units, Figure 5 illustrate.s an example oE contrast .~ heightening as taught by the invention, Figure 6 illustrates examples oE the contrast heightening in diEferent phases, lS Figure 7 shows various forms oE adaptation, Figure 8 present.s the means applying the procedure of the invention, at block diagram levell Figure 9 shows the block 8 oE Figure 8, at circuit diagram level, Figure 10 presents the sensitivity curve of the mean~ oE Figure 9, ~ue to different weighting o:~ the image :Eorming points, in the plane oE the door opening, Figure 11 shows the output signals oE the means o.E Figure 9.
The ba~ic design oE the lnvent;on may be embodied as a two-stage s,ystem with input.s and outputs related to each othe.r i.n a certain way. ~y employing pract:ical quantit.ies such as current, voltage and :Erequency ln connection with the input.q and outputs, the de,Einition Oe the sy~tem can be concretized a~ in Figure 1.
~ n input quantity is in the Eorm of a current io, and an output quantity is a .frequency El. A tap is provided at a point where a current il is .introduced and whlch has the voltage Ul. The two-stage operation is realized as shown by the formulae lnscri.bed in the block in such a way that the input quantity current io affects directly only the tap point voltage Ul if the current il is constant. The output fl is directly proportional to the current 11 (with the coe:~icient kl) When the tap is connected by an impedance either to a :Eixed voltage level or to the taps oE circuit operating in parallel, inteeaction is produced between the voltage Ul and the current il, by which the current il, and hence the output frequency fl, will change.
A circuit implementing the formulae given in Figure 1 is presented in Figure 2. An important feature of the circuit is a suitably selected tapping point, by the aid oE which the Eeatures of the basic circuit can be modified by the mutual interaction of the circuits operating in parallel in such a way that a plurallty of practical applications, which may be based on the interaction of a number of signals, ~ind a simple solution, The operation of the circuit depicted in Figure 2 can be described in the :Eollowing way, neglecting the diode threshold voltages and assuming that UO U1 (see Figure 3).
The voltage supply oE CMOS circuits 4,5,6 (e.g.
oE NOT type) is E, and the decision threshold of the circuit i.5 a~sumed to be E/2. The voltage Ul is tllen the diEEerential voltage between the deci3ion threshold and the capacitor C2.
By the aid of the capacitor C2, electric charge is pumped at Erequency fO Erom the capacitor C2 to the capacitor Cl. This produces a current, the average oE
which is io. IE UO U1, we .elnd:-~1.) io = Co*Uo*Eo ~'he voltage oE capacitor Cl at the beginning Oe the cycle is lower by the amount Oe Ul than the deci3ion threstlold E/2. With the current io, the capacitor Cl is charged to the decision threshold in the time:-~2) tl = ~Cl*Ul)/io After the time tl has passed, the capacitor Cl is discharged by the aid of the CMOS circui.ts, delivering the charge:-~Z97~79 g (3) Q = Cl*~, whereaEter it is once again charged through the diodes to a level WtliCh iS lower than the decision threshold by the amount Ul, thus starting a new cycle. In this manner, pulses are produced which have the frequency fl = l/tl.
The current that has been removed is tfrom equation 3~:-(4) Ql/tl = (Cl*E)/tl = il (at equilibrium) Hence, 1 il/(Cl E) = kl+il; kl = l/(Cl*E) that is, one oE the two conditions Eor tlle block oE Figure 1 has been Eound. From equations (2) and (5) we Eind fl = 1/t] = io/(Cl*U1) = il/(Cl*E), with Ul*il = E*io = ko io; ko 15 that i9, the other condition.
Since exact satisEying of the conditions of thefunction blocks requires that no current is introduced in the circuit through the input, the input quantity io has been generated by the aid of the capacitor pump. We may then according to equation (1) as the actual input quantity consider CO~ UO or fO if the other two quantities are kept constant. In the example, voltage and Erequency are constant, and capacitance is the variable input quantity, whereas when using sensors oE other types the output quantity oE the sensor can be converted e.g. into a frequency, applying a technology known in the art. In the example appllcatlon, the current Lo will according to equation (1) remain dependent on the capacitance only:
~6) io = k2 CO
By connecting the variou~ taps oE the basLc circuLts oE
E'igure 2 to each other through diEeerent impedance~ and by arranging suitable current supply points in the irnpedance or interaction network, a circuit Eor efEecting the pre-processlng oE the functionaL lmage inEormation is obtained, which at the same time serves as an analog/digital converter because the output is a frequency, which is directly appropriate to be processed digitally.
~Z~7~75~
In Figure 4 is presented the pre-proces~ing circuit ~or a one-dimensional capacitance image, at block level. To the tapping points oE the diEEerent blocks, the constant current i i~ supplied, and the points are connected with each other e.g. by a resistor ~. The distribution oE the constant currents i between diEferent channels is partly dependent on the voltages Ul..~Un. The frequency of the output El..Ofn oE each channel reElects the capacitances COl...COn oE the input pattern in the way that the frequency image that is obtained is p~incipally proportional to the second deriva-te oE the re~pective capacitance image.
In Figure S this relationship has been illustrated. In Part I there is shown a case in which the level oE the C pattern changes. This causes no changes in the corresponding f pattern. The change of the derivate ~slope) of the C pattern, taking place in Part II, also has no eEfect on the E pattern. Only when the derivate oE the C pattern 2 changes - Part II[ - will the addition to the f pattern of frequency components proportional to thi~ derivate be caused.
In Figures 6a - 6E have been pre~ented the steps in processing the image signal in an apparatu.s comprising slx capacitive antennas disposed to be the image Eorming points oE a one-dimen~ional lmage. It is seen in Figure 6a how the antennas see an object that has appeared adjacent to the third antenna: the capacitance C03 oE the third anterlna increa~es while the va]ues oE the other antennas ~tay substantially unchanged. IE we imagine lines entered between the capacitance value~ oE the antennas, we get a capac;tive image in which the anguLar changes between the point~ contain the inEormation which i8 essential from the point oE view oE the means oE the invention.
In Figure 6b, the charlges oE the capacitances have been allowed to be reflected in the output frequencies El - f6 of the capacitance/Erequency converters of Figure 2, the corresponding frequency image resulting thereErom. It is seen that ttle angular changes have increased compare~l with the capacitance image, that is, the contrast has been lleightened. This ~eature is produced by the aid of the interaction network.
In Figure 6c, the a~ter-processiny phase oE the exemplary apparatus has been reached, in which the Erequency image fl - ~6 that has been produced is converted into time differences between the image Eorming channels by measuring in synchronized manner the frequency image components on the basis oE the passage time diEEerences oE a given predetermined number oE pulses, in the present instance eight pulses. At the same time, ~requency/time conversion takes place.
In Figure 6d is shown how the time image obtained in the measuring phase has been converted by subtracting from each other the time quantities oE
mutually a~jacent points tl - t6, this process resul-ting in ive time diEference guantities tl2, t23, t34, t45 and t56. A procedure of this kind also contributes to higher contrast.
In Figure 6e, one mode oE weighting of the channels is presented, lower weighting factors (Kl, K2) having been assigned to the "marginal channels" compared with the ilnage Eorming points located in the centre Oe the image Eield (K3). rrhis i~ Erequently advantageous Eor the reason that the background Eactors in the marginal areas mayr owing to discontinuity, deviate strongly rom the central area oE the image, while at the ~nme time they are le~s sLgnificant from the point Oe view Oe operation, and thereEore decrea~ing their weighting factor will result in more reLiabl¢ operatlon oE tne apparatu~. The weighting factors are often fixedly set by component selection and component connections, while on tlle other hand the sensitivity a~justment S must be easy to accomplish, in order to optimize the operation.
Figure 6f presents the ultimate image in our exalnple of capacitive isnage processing. In the example, the object that has appeared in the vicinity o the third :
~2~ 7'~
antenna produces in the voltage image a voltage IJ3 which surpasses the decision threshold and thereby forwards indica~ion of the presence oE the ob~ect. The vol-ta~3e~
are produced by integrating, with reference to the digital S signal indicating the termination oE count;ng perEormecl on the ~requency fl - f6 of each channel, the time interval from the end of the counting on its frequency to that taking place in the next channel on a lower frequency, and that when the voltage oE any one channeL obtained in this manner by integrating exceeds the decislon threshold, an indication oE the appearance oE the object in the image fieLd is Eorwarded.
F'igures 7a and 7b illustrate the aclaptivity oE
the apparatus. If, as above, an object appears in front oE the antenna No. 3, the result is a frequency curve as plotted in solid lines in F'igure 7a. Normally, the smooth curve has been disturbed by a frequency rnodification corresponding to the extra capacitance which the object represents, as has been described in the foregoing. If the object which caused the disturbance remains in the image field for some time, the proEile oE the curve starts to flatten in the manner plotted with dotted lines in Figure 7a, until tne curve is once more a horizontal line. ~his phenomerlorl i~ due to the Eact that in the interaction network the connection Erom the image Eoeming channel to the other channels has been establislled by rneans oE
capacitor~, wh-~reby the extra eurrent Erom the neighbourillg channels cau~ecl local:ly by a high anterlna capacLtance wiLL not contlnue aEter tht3 current-pro(lucing voltage dLEEt3rellce~ betwet3n the interaction points have gone over to the capacitors. F'inally, the resuLt in tlle cast3 oE the curve undergoLng adaptation is a smooth Erequerlcy Lmage, even iE the object whictl caused the di~turbance sllould stiLl exist in the viewed object.
By adaptation, the eEEect oE ~lowly changing background disturbances can be reduced. IE the object is removed after the adaptation has taken place, a "hole"
corresponding to the object remains in the image field ~Z~79 seen by the antennas, the result thus being a "negative"
frequency image in which the disturbance constitutes a local minimum of equivalent size. This is useEuL, ~Eor instance, in the lift saEety edge to be described later on, as the door will not close at once aEter an obstacle that has kept the door open for a prolonged time.
Figure 7b presents a non-adaptive colnponent which is proportional to the capacitance value derived Erom the image Eorming points. This component appears and disappears immediately with the object that caused the disturbance. In addition, the relative eEEect oE said component on the ultimate Erequency image has in this case been adjusted to be less than that of the aaapting component, whereby only sizable disturbances produce a signiEicant non-adapting component. This component i~s useEul for the reason that iE, Eor instance, in the case oE a liEt a person keeps the door open, it is necessary that the door monitoring system is aware oE the person being still in the door opening, as otherwise the door would close when the disturbance caused by the person has ultimately faded due to adaptation.
The apparatus oE the invention is described in greater detaiL in the Eollowing by the ald oE an example, reference being made to Figures 8 to 11.
In Figure 8, a capacitive saEety edge to be installed on the llEt doors i~q concerned, the ultimRte Eunction oE which i8 to indLcate whether there is an obstacle in tlle door openLng or not when the door close~.
Currently, this functLon is implemented by mechanical "collisLon strips"~ by photocells or, Eor instance, by capacitive, independently o~erating or dLEEerentially operating sensors.
It is one oE the physicaL Eundamentals oE
capacitance sensing that the basic capacLtance oE the sensor is exclusively dependent on the area and ~hape o~
the antenna. The other capacitances that have to be taken into account in practical antenna constructions are the ~2~3 7~7~
basic capacitance of the circuit, the antenna protection plate capacitances and the disturbance capacitances.
A protection plate placed on one side oE t~le antenna plate reduces the eEEective area oE the antenna approximately to one-halE and prevents the antenna from detecting capacitances in the door structure, whereby the basic capacitance oE the antenna is reduced and its sensitivity improves. The adaptation, voltage protection and placement Eeatures comprised in the apparatus embodying the invention also contribute to higher sensitivity achievable in practice.
IE the door oE a liEt consists oE two halves moving towards each other, it is necessary to have one saEety edge 7 with image processing means 8 Eor each side.
If the door opens altogether on one side, one saEety edge i9 enough. Other equipment entities oE the system are a control rnens 9 and a power source 10. The voltage supply points oE tlle image processing means 8 oscillate in joint Eorm with reEerence to the grounded level, e.g. at 30 kHz requency and at 50 V amplitude (U12 and ~22), by which oscillation t~le pumping efEect oE electric charges is accomplished with tlle antenna capacitances. The voltages oE the cor-nection points oE the circuits 8 have been indicated by Ull and UL2, oE which more below, and reEerence numerals ll and 12 indicate outputs oE the control mean,s g.
In Figure 9 has been presented one circuit dLagram oE the image processing means 8 oE ~'igure 8 wlth its capacitlve antennas 7. I,et us conslder the pha3es ln proce~ing in th~ mean.~ the image signal produced in the second charlrlel Erom the top in the Eigure. It is assumed that the antenna has just registered that an object ha~
appeared in its image Eiel.d, by reglsterlng a dl~turbance ca~acltance.
The circuit block 14, which corresponds to the circuit oE Figure 2, acts as a "pump", which induces a certain immunity to electrical interEerence. In practical applications, this is oE great importance since no special ~:~g~
interference shielding is required and little attention need be p~id to freedom from dlsturbances of the zero level. The energy needed Eor the pumping is obtained Erom the voltage U12, which is a 50 V d.c. voltage pulsed at 30 kllz ~requency. From the volta~e pulses a current i2 passes through the diode D22, and this current "pumps"
charge into the capacitor C21.
When the antenna capacitance increases due to a disturbance capacitance, the current i2 increases in direct proportion thereto, according to Eormula ~1). The voltage corresponding to the voltage U1 of the interaction point P2 in F'igure 2, which was determined to be the voltage between the operating polnt oE the circuit and the interaction point, increases correspondingly. Elereby, the capacltors C22 and C12 supply an extra current component to the chanrlel that was disturbed, for attaining a new voltage at rest at the interaction point P2. rhis extra current supplied to the "disturbance channel" is Eelt not only in the discharging feequency oE the capacitor C21 oE
thi5 channel but al~o in the adjacent channels as a corresponding loss oE energy at their interaction points, resulting in a "negative" reaction in comparison with the disturbed channel. This eEeect can be compareci e.g. with the "]ateral inhibition" observed in bioloyical nerve systems, leading to heightening oE conteast.
After the new equilibrium voltage oE the interaction point P2 has been reached, the Elow oE currellt ceases between channels in the interaction network.
Simultaneous]y, the eEEect oE the disturbance capacitance ends. The disturbance ha~ now become adapted to blend with the backgrouncl image seen by the antenna. IE however a significant disturbance is concerned, which in the present instance would be at least a human hand in the immediate proximity oE the antenna, the increase oE U
causes a small current increase across the resistor R21.
The respective resistors of this and the other channels have been connected to a constant voltage on the terminal 13. The current component obtained Erom the constant voltage source over the resistor R21 does not adapt but Elows as long as the voltage Ul of the interaction point P2 is unchanged. By th,is extra component oE the current il of Figure 2, the non-adaptive Eeature is produced.
All said current components inEluence the discharging frequency of the capacitor C21 through the current i2, said frequency constituting the frequency component f2 oE the channel'in question. The frequency is counted by samples oE eight pulses, synchronou~ly, with octal counters 15, the time difEerences emerging from the count being interpreted as was described in connection with Figures 6c and 6d.
Immediately after the fastest channel tin the present instance that which has the output A2) has counted its eight pulses, the digital signal ~2 indicating termination of count begins to exert influence on the inverter circuit operating at an adjustable voltage level and which supplies current to the integration input 17 of the Erequency/voltage conve,rter 21, whereby the voltage U2 equivalent to the relative Erequency of the ctlannel with reference to the other channels begins to build up across the capacitor C23. The values oE the capacitors C13 - C63 in combination with the resistors R12 - R62 serve at the same time through their RC time constant.s as nnother weighting facility for di,EEerentiating the ~ensitivity oE
the channels.
~ tletl eight pulses oE the channel outputs ~2 - ~5 have been counted, all counters 15 have pulled thelr output up, which ls observed by the down~pull oE the output Oe the gate 16. ~rhls signals the pulse Eorming circuit 18 to deLiver A pu.L8e ~I synchronizing the reading mo~nent, to the disturbance detection gate 20. The same puLse aLso opens the outputs oE the image Eorming circults 14 to start R new Erequency counting cycle. The pulse forming circuit 18 also gives a command to the tumbler 19 to set the counters 15 to zero by a zeroing pulse R.
In a normal case with no disturbance, all inputs oE the disturbance detector 20 are thus at logical zero at ~L2~97~
the moment oE reading, whereby the N~ND gate 20 delivers a pulse to the transistor Tl in the output stage 22, which in turn by pulsing the voltage Ull inEorms the control means (Flgure ~, reEerence numeral 9) that there is no d iB turbance.
In the present instance, the volt~ge U2 surpasses the decision threshold at the moment when a pulse ~l arrives at the disturbance detector 21), which has the eEEect that no pulse is forthcoming Erom the N~ND gate 20. There~ore the pulse oE the output stage 22 also Eails to be eormed.
In Figure 10 has been depicted the coverage constituted by a safety edge with six antennas, the image forming channels having been weighted in the manner presented in the foregoing. The highest sensitivity has been arranged to occur at the image forming points located in the centre of the image Eield, for which points the maximum sensing distance a can be employe~ with the present apparatus, even in adverse conditions (e.g. an unstably moving closely positioned shaft door), depending on the antenna design, to be up to 100 mm.
Finally, in Figure 11 is presented the volt~ge Ull between the connection points oE the bLock 22 containing tl~e output stage, and voltage stabiLlzing circuits, in various situations; the Eunctions caused by its output pul~es in the control means 9 oE Figure 8 and typical voLtage and Ere~luency vaLues. 'rhe voltaye Ull ls adjustable Ln the range l6 - 22 V, by which adju~tment the volt~ge leveL at the point 24 is aEEected, WtliCtl supplies the invertLng circuits controllLng the integration inputs 17. The changeable voltage l.evel aEEect~ the dLsturbance detection sensitivity in the manner illustrated by Figure 6e. In the normal operating mode N, when the liEt door iB
open, pulse~ indicating the end Oe the measuring cycle and freedom Erom disturbances in the door opening occur at Ere~uency 120 - 150 Elz. When the lift doors close, the capacitance oE the antennas increases strongly in the region DC so that the frequency of the pulses increases to ~2~'7~
16 0 - 3 0 0 l-~ z . In a disturbed situat ion D, the pul~e~
cease, as was described above, and the ab~ence oE at least two consecutive pulses is interpreted in the control to be a ~listurbance requiring opening oE the doors.
When a disturbance occurs in tlle region D, the control mean~ 9 of Figu~e 8 pulls its output 11 down aEter a ~elay equivalent to about two missing pulses. The line returns to state 1 after the disturbance has ceased to act.
Wt-en the doors close, the pulse Erequency increases, whereby after a certain delay the control means renders the saEety edge inactive by pullin~ down the output 12~ This must be done because when the antenna capacitances increase stxongly, various disturbances oE
operatlon, difficult to predict, may occur. Since the saEety edges are not needed while the doors are closed, ttley can most appropriately be made inactive. In this case the line S merely indicates that the saEety edges are indeed out oE action. Here too the present apparatus aEfords the advantage that it distinguishes between the increase of the overall capacitance due to closing the doors and ~ disturbance capacitance due to an obstacle in ttle door opening, whereby thls function, too, becomes reLiable. The saEety edge is again made active aEter the doors open, with a certain delay.
IE the disturbance is on Eor longer than 20 secondsl or iE the summed disturbance de~ection time exceeds this ~ame value, the error checking circuLt F'S i~
switched on and it puLl~ the line 12 down. ~y the aid oE
thiC3 output, the unLt controlling the operation oE the door is inEormed that the sclEety edge is not Eurlctiona1, and it is then po.ssible to switch on e.g. a photocell to be the door-opening means.
ThereaEter, if there has been no obstacle or the obstacle ha~3 gone away, the doors are closed, and a check is made to ascertain whether the line S has gone up. If it has, the safety edge is most probably in order, an~
transition is made to the normal mode of operation, to 797~
checking the pulses oE Ull. l~ the image forming means i~
deEective, it is most unlikely that the saEety edge cut-out detector (the line S) is operative, and the saEety edge then remains subjugated to the error checking circuit FS. The error checking circuit may consist of A Eully previously known, simple logic circuit; thereEore, it will not be presented in any greater detail.
It is obvious to a person skilled in the art that diEEerent embodiments of the invention are not exclusively conEined to the example presented in the foregoing but may vary within the scope oE the claims presented below. Eor instance, the image Eorming may be implemented by means of any sensors or component~ suitable for image forming, such as phototransistors, photodiodes, photoresistors, etc. when the output signal produced by the sensors is converted e.g. into frequency. [t is also possible, applying existing techniques, to log-modlllate the signal iE its range of variation is very wide, before supplying it to the contrast image Eorming means oE the invention. ~'he contrast image Eormed by the aid of image point-speciEic Erequencies may also be aEter-processed in a number oE ways, e.g. Eor shape-identifying applications.
~ ~ .
Claims (16)
1. A method for producing an image based on contrast discrimination in an image forming means of at least one-dimensional image filed with discrete picture elements, comprising:
detecting an image signal for each said picture element to produce an output thereof;
applying a first electric current to an image forming channel having a tapping point with a voltage, said first current affecting a second current, having an output frequency, flowing into said tapping point of said image forming channel;
connecting said tapping point to corresponding tapping points of other image forming channels and simultaneously affecting said voltage of said tapping point, in such a manner that the product of said second current value and said voltage value is proportional to said first current value, and wherein the output related to said picture element has an output frequency proportional to the output frequency of said second current;
supplying a suitable current to an interaction network connecting, by means of suitably selected impedances, said tapping point of said image forming channel to the tapping points of the image forming channels of other picture elements, such that a desired contrast heightening of the image is achieved and such that said output frequency of each of said image forming channels combine to form a frequency image, which becomes the basic information for interpretation of the image by digital means.
detecting an image signal for each said picture element to produce an output thereof;
applying a first electric current to an image forming channel having a tapping point with a voltage, said first current affecting a second current, having an output frequency, flowing into said tapping point of said image forming channel;
connecting said tapping point to corresponding tapping points of other image forming channels and simultaneously affecting said voltage of said tapping point, in such a manner that the product of said second current value and said voltage value is proportional to said first current value, and wherein the output related to said picture element has an output frequency proportional to the output frequency of said second current;
supplying a suitable current to an interaction network connecting, by means of suitably selected impedances, said tapping point of said image forming channel to the tapping points of the image forming channels of other picture elements, such that a desired contrast heightening of the image is achieved and such that said output frequency of each of said image forming channels combine to form a frequency image, which becomes the basic information for interpretation of the image by digital means.
2. A method according to claim 1, which includes supplying to each tapping point of an image forming channel a constant current which produces a constant basic frequency component in the output frequency.
3. A method according to claim 1 which includes forming by the series-connected resistor-capacitor impedances of the interaction network a frequency component which is proportional to the angular changes of the intensity image composed of the original image signals and which, in the course of a time determined by the changes, adapts the permanent changes of the viewed object, thus contributing to a smooth image.
4. A method according to claim 3, which includes connecting to the tapping points of the image forming channels a resistor, one end of which has been connected to a suitably selected voltage level, by which a frequency component proportional to the absolute value of the image signals is produced.
5. A method according to claims 1, 2 or 3, which includes converting the frequency image into time differences between the image forming channels by measuring synchronously the frequency image components on the basis of the passage time differences of a given pre-selected number of pulses; obtaining conclusions concerning the changes occurring in the object that is being viewed by integrating, with reference to the time of the digital signal indicating termination of the counting performed on the frequency of each channel, the time interval from termination of counting at its frequency to that taking place at lower frequency in an adjacent channel; and providing, when the signal, thus integrated, of any channel surpasses the decision threshold, an indication of the appearance of an object in the image field.
6. A method according to claim 1, 2 or 3, which includes differently weighting image forming points located in different parts of the image field for achieving a desired sensitivity distribution of the image forming points.
7. A method according to claim 1 which includes employing, at the image forming points, capacitive antennas for producing a contrast image, said antennas identifying changes of capacitance in the environment and forming image signals thereof.
8. A method according to claim 7, which includes employing the capacitive image forming system based on contrast discrimination unidimensionally on the safety edge of a lift in the way that, at least on one side of a door opening of the lift, image forming points are disposed in vertical sequence, said points monitoring the entrance of people and objects in the opening of the lift door, and the image forming system, when it concludes that an obstacle has entered between the lift doors, informing a control system of the lift thereof.
9. A method according to claim 8, wherein the image forming means monitors the operation of the lift doors by independently monitoring the absolute values of the capacitances seen by the antennas in the door opening, and the duration of the obstacle indication, the safety edge being made inactive when the doors are closed, whereby the capacitance is distinctly greater than while the door is open, or when the aggregate duration of obstacle indications surpasses a pre-determined limit.
10. An image forming apparatus for producing an image based on contrast discrimination in a one-dimensional or multi-dimensional image field having individual image forming points for producing a one-dimensional or multi-dimensional image based on contrast discrimination, comprising:-one image forming channel for each image forming point;
said channels comprising signal/frequency converters for sensors at said points;
said converters comprising two-stage electric charge pumps having a first stage which is a producer of a current signal of the image forming point, and a second phase which is a frequency oscillator, the frequency which is variable by means of said current signal, and of a tapping point between the stages, or an interaction point, to which the tapping of one or several other converters has been connected over a suitable impedance for forming an interaction network; and interpreter means for interpreting an image produced by the channels and composed of frequencies.
said channels comprising signal/frequency converters for sensors at said points;
said converters comprising two-stage electric charge pumps having a first stage which is a producer of a current signal of the image forming point, and a second phase which is a frequency oscillator, the frequency which is variable by means of said current signal, and of a tapping point between the stages, or an interaction point, to which the tapping of one or several other converters has been connected over a suitable impedance for forming an interaction network; and interpreter means for interpreting an image produced by the channels and composed of frequencies.
11. An image forming apparatus according to claim 10, which includes means for separating, from the frequency image that has been produced, by the aid of the interaction network, an image component proportional to the changes in slope of the contrast curve, said component being maintained by a capacitance connected between the interaction points, and which therefore in the case of permanent changes is adapted out of the image within a certain period of time.
12. An image forming apparatus according to claim 10 or 11, wherein means are provided for separating from the frequency image obtained a permanent image component proportional to the absolute differences of the contrast curve, which is formed of the changes caused by the current of the image signal in the voltage across a resistor.
13. An image forming apparatus according to claim 10, wherein the outputs of the signal/frequency converters are connected to pulse counters, by the aid of which the frequency/time conversion can be carried out by synchronized pulse counting in the channels, a digital voltage signal indicating at each image forming channel the termination of pulse counting being connected to an analog time/voltage converter, which signal is integrated with reference to time during a period equivalent to the magnitude of the time differences between channels, in order to produce a voltage image proportional to the contrasts of the viewed object.
14. An image forming apparatus according to claim 13, wherein the analog time/voltage converter circuit (21) contains RC time constant circuits by which the signals (A1 - A6) obtained from different image forming channels can be assigned different weights.
15. An image forming apparatus according to claim 10, wherein the sensors at the image forming points are capacitive antennas by the aid of which capacitive changes in the environment are identifiable.
16. An image forming apparatus according to claim 15, wherein the safety edge of a lift is composed of a one-dimensional image forming system in such a way that at least on one side of the door opening of the lift are placed capacitive antennas in vertical sequence and by the aid of which the arrival of people and objects at the lift door can be monitored and information hereof forwarded.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000508515A CA1297979C (en) | 1986-05-06 | 1986-05-06 | Procedure and means for producing a contrast image |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000508515A CA1297979C (en) | 1986-05-06 | 1986-05-06 | Procedure and means for producing a contrast image |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1297979C true CA1297979C (en) | 1992-03-24 |
Family
ID=4133076
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000508515A Expired - Fee Related CA1297979C (en) | 1986-05-06 | 1986-05-06 | Procedure and means for producing a contrast image |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1297979C (en) |
-
1986
- 1986-05-06 CA CA000508515A patent/CA1297979C/en not_active Expired - Fee Related
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4753323A (en) | Safety system for closing doors | |
| US6298709B1 (en) | Sensor device | |
| US4044860A (en) | Elevator traffic demand detector | |
| KR100363287B1 (en) | Method for determining very low capacitance and the use thereof | |
| US4680806A (en) | Edge location measuring head | |
| US4217542A (en) | Self inverting gauging system | |
| US3115622A (en) | Panoramic scanning counter | |
| JPH0626381B2 (en) | Method and device for detecting transition of DC component in periodic signal | |
| CA1297979C (en) | Procedure and means for producing a contrast image | |
| US5099145A (en) | System disconnection detection circuit for a distributed location power source | |
| JPS6222509B2 (en) | ||
| FI79006B (en) | KOPPLINGSSCHEMA FOER TILLVERKNING AV ETT MOTTAGNINGSKRITERIUM. | |
| US4679032A (en) | Procedure and means for producing a contrast image | |
| US5359652A (en) | Tone receiver comprising a switch capacitor zero crossing detector | |
| EP0393558A3 (en) | Vertical synchronizing signal detector | |
| EP1093586B1 (en) | Integrated circuit with improved synchronism for an external clock signal at a data output | |
| US3525991A (en) | Converter | |
| US4454423A (en) | Circuit arrangement for a radiation detector | |
| US4104524A (en) | Circuit arrangement for a detector for ionizing radiation | |
| US4900943A (en) | Multiplex time delay integration | |
| US3829782A (en) | Electrocardiograph telemetry system having circuitry for indicating inoperative conditions | |
| CA1256608A (en) | Method and apparatus for monitoring an area in front of an elevator door | |
| US4231374A (en) | Procedure and device for the detection of extraordinary events in a series of essentially periodically recurring normal events | |
| JPH04207791A (en) | Luminance level measuring circuit | |
| JP3732244B2 (en) | X-ray imaging device |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed |