Optical transmitting and receiving device for the contact-free reading of marks

An optical transmitting and receiving device for the contact-free reading of marks, particularly marks and bar codes. The device has a transmitter diode arranged in a plastic body which directs an oblique transmission beam onto a reference surface outside the plastic body. A receiver diode is arranged at an angle to the transmitter diode in the plastic body, whose receiver beam is likewise directed onto a reference surface. Instead of a glass optical system simple rectangular slotted diaphrams are provided and the transmitter and receiver beams intersect at one single point of intersection in the region of the reference surface.

BACKGROUND OF THE INVENTION 
The invention concerns an optical transmitting and receiving device for the 
contact-free reading of marks and more particularly includes transmitter 
and receiver diodes positively positioned with their axial beams 
constricted by slots and intersecting at a reference surface for high 
resolution reading. 
Transmitting and receiving devices of this type are known from U.S. Pat. 
No. 4,079,261 and, in essence from IBM Technical Disclosures Bulletin Vol. 
14, No. 1, June 1971, Pages 58, 59. 
A disadvantage in these referenced structures is that the size of the 
rectangular cutout is still in the area of the dimension of the housing of 
the transmitter and/or receiver diode. This, combined with technical 
production inaccuracies in the edge area of the optical piece parts, which 
are mostly mass produced can lead to dispersion on the reference surface 
or to transition-time distortion on the receiver diode, both of which 
limit the accuracy and reliability of operation. Further, beam reflections 
can form disadvantageously on the inner face of the cutouts through which 
the beams pass which can impair the reading procedure with reference to 
the reading speed and resolution in the case of small markings. It is also 
disadvantageous that those cutouts, in the case of the known device, on 
the upper face of the plastic body, form differently-sized openings when 
compared with each other. Thus contamination can have a detrimental 
one-sided impairment of the beam path which with reference to the reading 
procedure causes slow-acting impairment which is often noticed too late. 
From French Pat. No. 25 55 337 the insertion of a frame with an optical 
slotted diaphram in the beam path of the transmitter and receiver diode is 
known. This is however disadvantageous in that reflections form on the 
side of the frame nearest to the optical parts, which can impair the 
accuracy of the reading. Furthermore, there exists the danger that the 
frame with the slotted diaphram could slide into the beam path. 
BRIEF SUMMARY OF THE INVENTION 
The invention is based on the technical problem of the further development 
of a device of the type mentioned in the introduction to achieve an 
increased reliability of operation and greater reading accuracy and 
resolution with low production costs. 
To solve the problem posed, the invention is characterized in that 
rectangular cut-outs are in the form of optical slotted diaphrams 
symmetrically arranged on the surface of the plastic body. The slots are 
of the same length and parallel to each other and have a width of about 
0.4 mm. The focal points of the transmitter and receiver diode are 
arranged to be equidistant from the corresponding optical slots. 
A feature of the present invention is that the slots emanate near the upper 
surfaces of the transmitter and receiver diode and from optical slotted 
diaphrams on the surface of the plastic body. This structural relationship 
prevents dispersions and reflections on the interior of the plastic body 
and also transition-time distortions. 
External interference which could affect the beam path, are extensively 
made symmetrical and the optical slotted diaphrams are kept small. Also 
achieved is that the differences in the optical function of the parts of 
the beam path, such as the transmitter and receiver, have only minimal 
influence, so that parts of differing optical behaviour can be used, 
particularly after replacement. 
A further feature of the invention is that the transmitter and receiver 
beam intersect at one single point of intersection in the area of the 
reference surface, thus achieving excellent resolution. The arrangement of 
rectangular slotted diaphrams as compared with circular apertures has a 
further advantage in that the intensity of illumination is much higher as 
compared with circular apertures. This is especially advantageous when it 
is necessary to recognise line-type marks such as barcodes. 
With slotted diaphrams print of lesser quality can be read better than with 
circular apertures, in that small printing errors are compensated for. 
In the following description the invention will be further explained by 
means of the drawing illustrating merely one embodiment example. Further 
features and advantages of the invention arise from the drawing and its 
description.

DETAILED DESCRIPTION 
FIG. 1 shows a plastic body (1) in which two recesses incline towards each 
other at the same angle with respect to a vertical axis (6). The 
longitudinal axis with each cavity or recess (3) (2) forms a beam path 
(23) for the transmitter diode (4) set into the recess (3) and a beam path 
(24) for the receiver diode (5) set into the recess (2). 
Both diodes (4) (5) are seated in a positive fashion in corresponding 
recesses (13) (11) of reduced diameter which continue the respective 
recesses (3) (2) in the plastic body. 
The transmitter diode (4) generates the beam path (23) which forms, with 
the vertical axis (6), a point of intersection outside and above the 
plastic body (1). 
The longitudinal axis of the recesses (2) (11) is so aligned that receiving 
diode (5) in the recess (11) sits on a receiving beam or axis (24) which 
intersects at the point of intersection (7). This point of intersection 
(7) is at a distance (8) from the surface (15) of the plastic body (1). 
It is important that the focal point (12) of the receiver diode (5) lies 
relatively far away from the rectangular slotted diaphram (10) so that, 
seen from this point (12) in the direction of the slotted diaphram (10), 
the reading area is kept relatively narrow thus giving high resolution. 
The transmitter diode (4) sits with its focal point (14) as close as 
possible to the slotted diaphram (10) in order to generate a high luminous 
density at the point of intersection (7). By means of the inserted slotted 
diaphram (9) however, only a narrow beam path (23) is generated at the 
point of intersection (7). 
As seen in FIG. 2, both slotted diaphrams (9) (10) are approximately 
rectangular and are arranged in the area of a relatively narrow face (15) 
of the plastic body (1). From this face originate inclined side faces (25) 
(27) so that the face (15) is formed from a truncated pyramid. 
The reason for this measure is to enable a distance wheel (16) to be 
arranged near one side edge of the face (15), which is rotatably mounted 
on the pivot axis (17). 
The circumference of the distance wheel (16) passes through the point of 
intersection (7) whereby this distance wheel rolls on the reference 
surface (26) to be read. Thus it is ensured that the plastic body (1) 
always has the same distance (8) from the reference surface (26) with the 
point of intersection (7). 
It is preferred if the transmitter and receiver beam paths each form an 
angle (28) of 30.degree. with reference to the vertical axis (6) which 
effectively bisects the intersection (7) of beams (23) and (24). 
FIG. 3 shows a schematic electric evaluation circuit in which the 
transmitter diode (4) transmits a continuous light. It is preferred here 
if the transmitter diode (4) is formed as a green light emitting diode. 
The receiver diode (5) is adjacent to the input of an amplifier (20) whose 
output signal is differentiated through a condenser (18). This 
differentiated signal is applied to the input of a Schmitt trigger (21) on 
whose output (22) is a digital pulse-signal. The control electrode of the 
Schmitt trigger is adjustable by the potentiometer (19). 
The described reading arrangement therefore gives a result which is 
economic, relatively contamination-resistant and of high resolution, with 
which it is possible to achieve a resolution of 0.2 mm with a slot width 
of the slotted diaphram (9) (10) of approximately 0.4 mm. That is, 
barcodes can be read which are 0.4 mm wide and which have a distance from 
each other of likewise 0.4 mm. 
It is a requirement here that the distance (8) is approximately between 0.5 
and 0.7.