DE1183256B - Device for non-contact measurement of the length or changes in length of an object - Google Patents

Description

FEDERAL REPUBLIC OF GERMANY

GERMAN

PATENT OFFICE

EDITORIAL

Boarding school Kl .: G Ol d;

GOIb
German KL: 42 d- 1/15

Number: 1183 256

File number: P 28596 IX b / 42 d

Filing date: November 27, 1958

Opening day: December 10, 1964

The invention relates to a device for contactless measurement of length or changes in length an object by means of two, each with an electrical receiver, an assigned field of view in the area of an edge of the object periodically scanning and measuring signals according to the Position variables for the scanned object edge within the field of view delivering transducers and with a summing circuit for the additive superimposition of the measurement signals supplied by the two transmitters.

In a known arrangement of this type, this is done by the receiver when the measurement object is detected The jump signal supplied is used for display immediately after it has been amplified and cropped accordingly.

In practice this brings not inconsiderable difficulties, especially due to the fact that the increase the jump signal is more or less steep, depending on the size of the amplitude of the jump signal, e.g. B. each according to the temperature of the rolling stock to be scanned. The known arrangement includes for this purpose a complicated circuit which switches the position corresponding to the half-width of the pulses to the Specifies the range in which the amplitude limiter works. It is also the case with the known arrangement necessary to amplify the receiver signals largely undistorted. That makes you relative complicated amplifier and results in an unfavorable noise level.

Furthermore, a device for the optical determination of hot rolling stock is known, in which two photoelectric transducers are arranged so as to be movable in opposite directions on a frame extending transversely over the rolling stock and are aligned with the two edges of the rolling stock. Each transducer contains an objective which images the edge of the rolling stock on a diaphragm with a rectangular opening. This opening can be covered more or less by means of a cutting edge that can be adjusted by a follower motor. The light passing through the opening falls on a first photocell. Light from the rolling stock falls through a second opening of constant size onto a second photocell. The follower motor is controlled by a signal according to the difference in the photocell signals. When the rolling stock passing through becomes wider, the first photocell "sees" more rolling stock in its field of view determined by the free aperture, ie it receives more light. A difference signal then arises and the follow-up motor adjusts the cutting edge so that the field of view of the photocell becomes a device for contactless measurement
the length or changes in length of a
Object

Applicant:

Marcel Charles Pfister,
Eckbolsheim near Strasbourg (France)

Representative:

Dr. F. Pommer, lawyer,

Düsseldorf-Gerresheim, Heyestr. 52

Named as inventor:

Marcel Charles Pfister,

Eckbolsheim near Strasbourg (France)

is narrowed until the difference signal disappears. In this way, the position of the diaphragm provides a measure

as for the position of the edge of the rolled material and can be used with any appropriate means are indicated. From the in this way from the two transducers The position determination signals obtained can be used to determine the width of the rolling stock.

This arrangement also has shortcomings: The field of view of the transducers is severely limited, because with a large field of view the control signals for the follower motor would possibly result from one only a small change in position of the rolling stock edge in one direction or the other than Difference between two relatively large signals because one large field of view of the first photocell (large aperture) already in the zero state a relatively large luminous flux falls on the first photocell, whichever is compensated by a correspondingly large luminous flux on the second photocell. It is it is evident that this would severely impair the accuracy of the arrangement. For this Basically, the transducers in the known arrangement are displaceable in opposite directions, so that they in the are essentially already aligned with the edge of the rolling stock. Furthermore, in the known arrangement Position of each rolled stock edge determined by mechanical adjustment. Such a comparison is natural always afflicted with a certain indolence. It often happens that the goods passing through performs relatively fast fluttering movements without

408 757/153

to change its width. In this case, both must Measuring transducers with their cutting edges try to mechanically follow these fluttering movements, although the measured value actually sought does not change at all, and this often presents considerable difficulties.

The invention is based on the object of avoiding these disadvantages of the known arrangements.

Based on an arrangement of the type specified, the invention consists in that the Edges of the object are scanned in opposite directions from the outside to the inside by the two transducers and that two bistable electrical switching devices by each of the receivers at Detection of the assigned object edge delivered signals from a first to a second switching state switchable and by a reference signal corresponding to the sampling frequency in the first Switching state can be reset and one of the measuring signals to be superimposed in one of the switching states deliver.

In the arrangement according to the invention, only those are generated by differentiation from the jump signal gained impulses used. These can be shaped and reinforced by known means. These Pulses operate an electronic switch, e.g. B. a thyratron. Once the thyratron has ignited then it no longer has any influence on the current flowing through the thyratron which signals then get onto the grid of the thyratron. The thyratron burns until it crosses zero the AC supply voltage (the reference signal) is deleted. So you are independent of that Temperature of the rolling stock or the like, as the signal generated by the receiver after the thyratron has been ignited remains without any influence on the measurement. The current through the thyratron is only made by the The voltage applied to the thyratron and the switching elements of the thyratron circuit are determined. For the circuit according to the invention is thus only the position of the steep edges of the pulses, but not you further course decisive.

By scanning in the opposite direction it is now achieved that the thyratron actually only through the when detecting the edge of the measurement object generated pulse can be ignited. The temperature of the roller table or the like is low and can be viewed as constant and in any case has no jumps that could generate an ignition pulse. The temperature and radiation of the test object, ζ. Β. of a rolled sheet metal strip, but does not need to be constant over the entire area. There may be dark or colder spots on the metal strip, which also result in sudden changes in intensity and ignition pulses on the thyratron can have. When the two transducers have their assigned fields of view (which also overlap can) would scan in the same direction, then one of the scanning beams would always have to pass over the object to be measured run before it reaches the edge of the field of view to be scanned. In such a case it could it can happen that the thyratron is already being scanned over instead of when sweeping over the edge of the measurement object such a spot is ignited. When the edge of the measuring object is detected, then appears again an impulse, which is then given to the grid of the already burning thyratron and without every influence remains. Incorrect measurements can then occur.

Expediently, independence from a supply voltage is achieved in that the output voltage the summing circuit is counteracted by an adjustable partial voltage that of the resulting differential voltage a servomotor is controlled, which tap the voltage divider adjusted, the position of the voltage divider tap as a measure of the to be determined Dimensions is used, and that the voltage divider ίο is applied to a rectifier arrangement that is of the the same power source is fed as the two transducers.

The invention makes it possible to continuously control the width of rolled sheet metal strips, yet before the tapes run on a reel. Thereafter, the rolling mill can then be set up to operate and any discrepancy will be corrected immediately; it is well known that the width of such bands often has to be adhered to very precisely. Another application is to measure thickness of wound rolls, e.g. B. of sheet metal strips wound on a reel.

An arrangement according to the invention can also be used to measure the length of pipes. It is well known that when pipes are rolled there are large differences in length and accordingly different wall thicknesses. The pipes are then measured and sorted, which in practice is very cumbersome and time-consuming and contains considerable sources of error. These disadvantages are with to avoid a measuring device according to the invention. Because the length measurement is very fast is obtained, it is possible to correct the rolling stock on the basis of this measured value in order to be as uniform as possible To obtain final products.

An embodiment of the invention characterized in the claims is shown in the figures and described below:

F i g. 1 schematically shows the structure of a probe head used in the invention;

F i g. 2 shows the associated circuit for obtaining a measured value for the position of the rolling stock beach;

Fig. 3 shows the arrangement of the probes, and Fig. 4 shows a circuit for forming a Width measurement.

The optical and mechanical structure of the photoelectric transducer used in the invention is shown in FIG. 1 shown purely schematically. A measuring beam 1 is collected by a cylindrical lens 2 on a polygon mirror 3. The axis of the cylindrical lens 2 is crossed to the axis of the polygon mirror 3. From the polygon mirror 3, the beam is transmitted via a cylindrical HoM mirror 4 to a radiation receiver 5, e.g. B. thrown in the form of a Pbs cell. The axis of the cylinder 4 is arranged to be crossed to the axis of the cylinder lens 2. Due to the effect of the two crossed cylinders 2 and 4, an exact punctiform focusing of the beam 1 is always obtained at the radiation receiver 5, regardless of how obliquely the beam 1 is incident according to the position of the polygon mirror 3. If, instead, one wanted to focus by means of spherical lenses or spherical mirrors, a more or less pronounced coma would always be obtained with a very oblique incidence of the beam 1. As a result, the pulse delivered by the radiation receiver would be fuzzy, what

for some of the applications of the invention described below is not acceptable.

The polygon mirror 3 is designed in the shape of a truncated pyramid and is formed by ten plane mirrors. It is driven by a motor 6 via a transmission 7. The engine 6 has a relatively high Speed of, for example, 3000 rpm and is reduced to 600 rpm by the gearbox 7. On the A fan 9 is seated on the output shaft 8 of the transmission 7

The pulses 13 are picked up via a line 14 from the actual probe head. To oppression of interference voltages that can be induced in the line 14, filter elements are provided, which are indicated schematically with 15. The impulses then reach the grid of an AC amplifier 16. This supplies a voltage roughly corresponding to the oscilloscope image 17. The Voltage according to 17 is on the grid of an overdrive

or some other additional load, through io th amplitude limiter tube 18. This provides one which the backlash in the transmission is suppressed. A sufficiently smooth run can be achieved when the voltage is applied to, for example, the oscilloscope image 19
to achieve the mirror, as it is absolutely necessary for some applications of the invention.

The motor 6 is a synchronous motor from the network 15 so that it is practical on the flanks of the curve is fed. result in vertical jumps. Used in practice

speaks. But one has to imagine that in reality the amplitudes are much larger, as shown in the oscilloscope image 19,

In the arrangement described, a viewing angle of 72 ° is scanned, with a

Frequency of 10

600

= 100 Hz. The

several amplitude limiter tubes connected in series, one of which is here for the sake of simplicity sake only one, 18, is shown. The thus obtained

ao signal 19 becomes a. Differentiator in the form of a transformer 20 is supplied, on the secondary winding of which positive and negative pulses according to the oscilloscope image 21 are obtained.
It should be noted that phase shifts that can arise in the individual amplifier stages and the transformer do not interfere, since these can be compensated for by appropriate adjustment of the angular position of the polygon mirror 3 (Fig. 1). The mirror 3 is opposite for this purpose

catcher 5 reaching beam 1 always runs in the same direction, z. B. from back to front in Fig. 1.

The type of receiver used depends on it
from what kind of objects are scanned. at
Self-luminous objects, for example glowing rolling stock, can advantageously be fitted with a resistance cell
Use (lead sulfide cell). It. then migrates to
a rotation of the mirror 3 only the solid angle detected by the photocell, that is to say the 30 of the axis 8 adjustable. The negative impulses 21 axis of sensitivity. In the case of non-luminous objects are cut away by a rectifier 22 , an auxiliary light source can be provided. To this end, a signal according to the oscilloscope image 23 can be used for this purpose, as shown in dashed lines in FIG. The phase position of the impulses according to FIG. 23 depends on the position of the targeted object in the vicinity of the receiver 5 in that of the lamp 10, which over a field of view detected by the probe head. Translucent mirror 11, the cylindrical mirror 4, the beam from the network (~), which also feeds the synchronous motor 6 polygon mirror 3 and the cylindrical lens 2 a light (Fig. 1), are emitted via a transformer24. This is reflected or genicht with center 25, two thyratrons 26,27 reflected, depending on whether the beam 1 is fed genphasig. In the oscilloscope images 28, the object falls on or not. For this purpose 40 29 the curve of the anode voltage of the two can be shown, for example, a triple thyratrone 26, 27 behind the object. The control grid of the retro-reflector should be arranged, which reflects the light hitting it thyratrone 26,27 received by a power source, so that the light 30 has a negative bias, so that the thyratrone on the drawn path back to the radiation trone normally are locked. The control receiver 5 falls as long as the light beam 1 has not yet detected the object grating via resistors 31, 32. tive impulses 23 given.

Another possibility, also non-luminous. The mains voltage 28, '29 has 50 Hz. The pulses

To capture objects consists in coming behind with a frequency of 100 Hz.

Object an extended light source, e.g. B. one of these are the thyratrons 26,27 in the half

Fluorescent tube or glow rod is arranged, 50 wave a pulse 23. The pulse is sufficient to

which of the sensitivity axis 1 periodically ignite the thyratrone 26, 27 , but of course only,

is scanned, the receiver 5 also if and as long as the anode voltage 28.29 posi-

is shaded as soon as the sensitivity axis 1 is tive. Since the thyratrone 26,27 is controlled by the transformer

detected the object. mator 24 are fed out of phase, ignite the

As an example, the switching of the transducer is 55 thyratrons always alternating. The first pulse 23

shown schematically in FIG. The thyratron 26 ignites, which burns so long,

Signals occurring at individual points of the circuit until the anode voltage 28 goes through zero again

are drawn in as oscilloscope images. (Oscilloscope image 33). The second pulse 23 ignites

The receiver is denoted by 5 (Fig. 2), which accordingly controls the thyratron 27 (cf.

is formed by a resistance cell (Pbs cell), 60 fig. 34). Thyratron 26 can with the second pulse

which changes its resistance when exposed to radiation. do not ignite, because at this moment the

This results in one of the resistor anode voltage 28 being negative.

cell 5 and a resistor 12 formed chip Depending on the phase position of the pulses 23 in relation

Voltage divider pulses according to oscilloscope picture 13, the thyratrons burn to the mains voltage 28,29

every time the beam 1 (Fig. 1) the 65 26.27 more or less long. Comes the ignition

DUT detected. It is to be assumed that
the test object is a self-luminous body, e.g.
is a glowing billet in a hot rolling mill.

impulse immediately, as soon as the anode voltages have become positive, the thyratrons practically burn during the entire half-wave, the pulse comes

only shortly before the voltage goes through zero again, the thyratron extinguishes immediately, it practically does not burn at all. The arrangement thus represents a phase-controlled full-wave rectifier. The measurement voltage U (FIG. 2) is thus a measure for the phase position of the pulses 23 and thus for the position of the targeted object in the field of view of the probe.

Instead of two thyratrons fed in phase opposition, two thyratrons connected in antiparallel can also be used are provided.

In Fig. 3 and 4 are the structure and circuit of a width measuring device according to the invention schematically shown. The arrangement contains two probe heads 54, 55, of which in FIG. 3 only one to see and that run in opposite directions. While the beam of a probe head 54 from left to migrates to the right, that of the other, 55, migrates from right to left. Since it is here on great accuracy arrives and in order to be independent of the distance of the ao measurement object 56 (Fig. 3), is the probe directed upwards on a parabolic cylinder mirror 57, so that the beam in the direction the arrows (Fig. 3) moves parallel to itself.

The probe 54 supplies a voltage U _5i which is proportional to the distance X of the left edge of the measurement object 56 from the right edge of the field of view. Correspondingly, the probe delivers a voltage U ₅₅ which is proportional to the distance Y of the right (FIG. 6) edge of the measurement object from the left edge of the field of view. If G denotes the width of the entire scanned field of view and b denotes the width of the measurement object, as can be seen immediately

X + Y ^ b + G,

that is, the sum of X + Y simply depends linearly on the width of the object to be measured.

The output voltages EZ ₅₁ and U _{65 of} the transducers 54, 55 are accordingly shown in FIG. 4 connected in series. This sum voltage is countered by a partial voltage that is taken from an adjustable potentiometer 58. The potentiometer 58 is connected to a rectifier 59 . The rectifier 59 and the transducers 54, 55 are all fed by one and the same network, as shown in FIG.

From the differential voltage of the rectifier 59 with the potentiometer 58 on the one hand and the transducer 54 and 55 on the other hand, a servomotor 61 is controlled via a zero amplifier 60, which the Potentiometer tap adjusted. The travel is linearly dependent on the width of the measurement object 56. Of the Servomotor 61 can therefore synchronously with the potentiometer tap the pointer of a display device adjust. If necessary, the display device can be made very large. It is yes it is often desirable that the measured value obtained can be read off from a distance.

For the measurement of long lengths (pipes) the transducers 54, 55 are in the plane of the paper (Fig. 3) arranged offset and measure only the deviation from a normal length. On the principle the measurement and the circuit (FIG. 4) do not change anything.

The measuring arrangement described has a very good accuracy. With special precautions by which a smooth running of the polygon mirror is ensured and the above in connection with F i g. 1, deviations in width of less than 1 mm can already be measured in the case of a sheet metal strip.

Claims (3)

Patent claims: 1. Device for non-contact measurement of the length or changes in length of a Object by means of two, each with an electrical receiver, an assigned field of view in the Periodically scanning area of an edge of the object and measuring signals according to the Length variables for the scanned object edge within the field of view delivering transducers and with a summing circuit for additive superimposing of the measurement signals supplied by the two encoders, characterized in that the edges of the object are through the two transducers are scanned in opposite directions from the outside to the inside and that two bistable electrical switching devices by each of the receivers when detecting the assigned object edge signals supplied can be switched from a first to a second switching state and into the first switching state by a reference signal corresponding to the sampling frequency are resettable and in one of the switching states of one of the measurement signals to be superimposed deliver. 2. Apparatus according to claim 1, characterized in that the bistable switching devices thyratrons are ignited by the receiver signals in a manner known per se and that the reference signal is an alternating voltage feeding the thyratrone at its zero crossing the thyratrone to be reset in the deleted state, and that the to be superimposed Measurement signals are the mean DC values of the currents flowing through the thyratrone, 3. Apparatus according to claim 2, characterized in that the output voltage of the Summing circuit an adjustable Teilspannoag is switched against and that from this resulting differential voltage a servomotor (61) is controlled, which the tap of a Voltage divider (58) adjusted, the position of which serves as a measure for the variables to be determined, and that the voltage divider (58) is applied to a rectifier arrangement (59) which is of the same The current source is fed like the two transducers (54,55). References considered: British Patent No. 795,525; U.S. Patent No. 2,791,931. 1 sheet of drawings 409 757/153 12.64 © Bundesdruckerei Berlin