DE4240803A1 - Detecting position of moving print- or read-head esp. in office machine - providing head with light source, which directs focussed light into waveguide for total internal reflection towards photodetectors located at both ends of waveguide, and sensing changes in detectors signals - Google Patents

Abstract

Measurement signals generated from an optically-scanned scale are used to trigger a printing or reading process. A light source (1) is moved with the print head (2), and the focused light from the source is optically deflected by total reflection along the motion axis (10) to at least one photodetector (7,9). The position of the print or read head is evaluated from the changes in signal of light pulses. The speed and acceleration of the head can also be determined using a time measurement simultaneously with the position measurement. USE/ADVANTAGE - Esp. for use in office machines. Accurate measurement result is achieved in digitally processable form using small number of inexpensive components in simple, low-cost design.

Description

It is known to determine the position of a moving printhead or reading head, especially in an office device, within a Print line to generate measurement signals that trigger a print or Read process can be used. Here one moves with the Printhead carriage along permanently connected optical position encoder a ruler that runs parallel to the side walls of the printer Platen is cocked. The ruler has a narrow tolerance division of 0.2 mm. The digitized signals from the optical position transmitter are 90 degrees out of phase with each other by position increments and To be able to derive reversals of direction.

These linear scanning signals are combined in one application-specific control electronics circuit Print command control, positioning and speed control processed (PKI Technical Notice 3/1989, pages 28 to 30).  

To control the position of a printhead has also been used up to now a clock disc detects the position of the driving electric motor, with disadvantages of the mechanical games in the drive systems of Toothed belt, spindle or gear are connected. For timing belts that form a vibration-sensitive mass-spring system adverse vibrations. The timing disk encoder is also used in a printer only indirectly detects the position of the print head and controlled, with a simple improvement in accuracy and Resolution is only possible to a limited extent and is very time-consuming to achieve would.

The invention specified in claim 1 addresses the problem that resulting from vibration-sensitive components and empty games Avoid disadvantages and create a system that works with one the smallest possible, cost-saving number of components and one uncomplicated construction.

The advantages achieved with the invention are in particular that an exact result is achieved in digitally processable form, being a small number of cost-saving components and a uncomplicated construction with considerable space saving and low Manufacturing costs can be achieved.

An advantageous embodiment of the invention is in claim 2 specified. After this it is possible that when evaluating the pulses for the respective position of the print or read head in connection with a simultaneous time recording also the speed and the Acceleration of the respective printing or reading process added becomes.

The processing property based on the light source is also  thereby increased that the light emitted by the light source through Entry into an optical fiber in light of a different wavelength will be changed.

The invention further relates to a device for controlling a back and forth movable carriage, a print head and / or a read head carries with an optically scanned scale and a receiver for that Measurement signal, which is in an evaluation electronics for controlling the Drive movement of a sled motor and / or the actuation of Printing elements can be entered.

The above-described method for determining the position is especially due to the low mass of the individual parts required influenced, so that it is advantageous if a light source together is movable with the carriage for the print head or the read head if the light source is directed perpendicular to the axis of movement of the carriage is and when focused light rays by deflecting means along the Axis of movement can be reflected on at least one photodetector, whose output signals can be switched to evaluation electronics.

The aim of the invention is also achieved in that on the Movement path a divider device consisting of translucent and opaque sections. Such Divider device can be implemented in various modifications become.

It is also advantageous that the light source consists of a light emitting diode, a Laser diode or a small incandescent lamp is formed.

The division device is implemented in such a way that the Divider means a mask made of translucent and  opaque arranged in the direction of the axis of movement Has sections and parallel to one another in the direction of Optical fiber extending axis of movement is arranged.

The steering of the light waves from a current location of the Light source in a photodetector is advantageously used for this purpose designed that the deflecting means from a fluorescent There is an optical waveguide along the axis of movement of the print head, wherein typically fluorescent dye molecules in the optical waveguide low, even concentration in an optically clear plastic or distributed in glass.

It is also proposed that a narrow-band photodetector optical filter is assigned, which is in the range of Fluorescence wavelength transmissive and directly on the end faces of the Optical fiber is applied.

The deflection of the light waves can also be designed such that a End of the optical fiber is completed by means of a mirror.

Other features of the invention are that the divider directly by mechanical, chemical or photographic means the optical fiber is applied in the direction of the axis of movement.

Further advantages result from the fact that the fluorescent Optical fiber from two concentric cross-sectional areas different refractive indices is formed, such that the radial inner refractive index larger than the radially outer refractive index is.

The manufacture of the optical waveguide and the divider device will  moreover connected by the optical waveguide Has polygonal cross section, the divider on a the polygon surface is applied.

The forwarding of the measurement signals can also be advantageous be designed by at least one on the optical waveguide Another flexible optical fiber or a fiber bundle from further optical fibers is connected.

Different signal forms for additional measurands to be determined can also be achieved by the fact that from a mask existing divider device one with one or more stages Provided slot shape, which has a slot width projecting Light source profile is opposite, so that the output signal also is present in stages.

The production of the few individual parts is with regard to the Optical fiber advantageously designed by the Optical fibers alternating successively from doped wafers made of fluorescent material and undoped discs, d. H. out crystal-clear material, is composed.

Embodiments of the invention are shown in the drawing and are described in more detail below. Show it

Fig. 1, the Inventive principle in conjunction with a print head,

Fig. 2 is a block diagram of an optical sensor,

Fig. 3 is a side view of the light source optical fiber print head unit,

Fig. 4 is a simplified plan view of the optical waveguide,

FIG. 5a is a formed as a mask, dividing means in detail,

Fig. 5b to the Fig. 5a associated time-current diagram,

Fig. 5 shows a cross section through a circular light waveguide with an integrated splitter means,

Fig. 7a shows a longitudinal section through the same arrangement with two photodetectors,

FIG. 7b is a graph of the resultant average output currents,

Fig. 8a is an alternative embodiment of the fiber optic splitter means and

FIG. 8b to FIG. 8a resulting output current history.

The perspective view according to FIG. 1 shows the optical positioning system according to the invention. A light source 1 consists, for example, of a light-emitting diode, a laser diode or a small incandescent lamp, the light of which - suitably focussed - is thrown via a light beam 4 onto an optical waveguide 5 in addition to a print head 2 (reading head) which prints a receipt 3 . It goes without saying that the light beam 4 can also be deflected via mirrors or prisms or can be brought to the optical waveguide 5 by means of a (more or less long) optical waveguide. Furthermore, a divider device 6 is assigned to the optical waveguide 5 , which consists of translucent and opaque subregions, which are usually equidistant, either applied directly to the optical waveguide 5 , which, for. B. can be done by screen printing or is arranged as a separate component directly in front of the optical fiber 5 parallel to the optical fiber 5 . The optical waveguide 5 is suitably doped with fluorescent dye molecules, which generate the optical measurement signals to be evaluated and transmit them by total reflection, preferably along a movement axis 10 in the direction of two photodetectors 7 and 9 . Against sources of interference are the photodetectors 7 and 9 with suitable optical filters 8, the narrow-permeable in the regions of the fluorescence wavelength, but particularly in the region of the exciting light source impermeable, is provided and a is the optical waveguide 5 is applied, if necessary directly on the ends. 5

The indicated in Fig. 1 divider means 6 is shown in FIG. 5a, in one embodiment as a mask 6 a in front of the optical fiber 5, in which a number of light-transmitting areas by slots 22 which allow the passage of the excitation light, and a plurality of opaque areas by means of Web 23 are attached between the slots 22 for blocking the light beam 4 . Suitable widths of slot-bar arrangements also result from FIG. 8a. They allow the detailed determination not only of the position of the printhead 2 but also of the direction of movement of the printhead-light source arrangement up to the detection of boundary or initial conditions.

As shown in FIG. 1, the arrangement of the light beam 4 can take place opposite to the direction of action of the printing elements of the print head 2 on the surface 11 of the document 3 .

According to FIG. 2, a block diagram of the optical fibers 5 of the light source 1 is in the form of opposite and the latter, together with the printing head 2 shown movable, wherein the optical fiber 5, the optical filter 8 and the photodetector are assigned. 7 Drive electronics 17 are connected to the print head 2 and a supply 19 for the light source and evaluation electronics 20 are connected to the light source 1 . The photodetector 7 works here with a mirror 21 to increase the intensity. The dividing device 6 is connected between the light beam 4 and the optical waveguide 5 .

As shown in FIG. 2, one end 5 a can be closed off by mirror 21 , which either forms its own component or is applied directly to end 5 a of optical waveguide 5 . This plane mirror reflects the fluorescent light back into the optical waveguide 5 at the same angle of reflection as the angle of incidence of the fluorescence falling on it; Thus, this light is effectively guided within the permissible angle for total reflection within the optical waveguide 5 , brought to the photodetector 7 and thus contributes to increasing the intensity of the measurement signal to be evaluated - with negligible attenuation within the optical waveguide 5 up to a factor of 2.

FIG. 3 shows a side view with a section through the light source 1 , the divider device 6 , here as a mask 6 a in front of the optical waveguide 5 and thus represents an independent component. Furthermore, a drive 12 of the print head 2 is shown above the line 11 .

As can be seen from FIG. 4, the divider device 6 has a number of translucent areas, namely the slits 22 , which allow the passage of the light beam 4 to excite the fluorescence, and between them a number of opaque areas, namely the webs 23 between the slits 22 that block the light beam 4 .

Referring to FIG. 5a is a linear dividing means 6 with a regular, equidistant here structure of rectangular slots 22 and ridges 23 is formed with the same width. In Fig. 5b, the associated output signal 24 is shown at the photodetector 7 and 9 respectively.

Referring to FIG. 6 shows a further alternative of a dividing means 6 is shown as part of the optical fiber 5 itself, that is integrated in the same. This arrangement consists of two sections, an inner core 5 b, the fluorescent optical waveguide 5 made of glass or plastic with a suitable refractive index n1, which is chosen so that this refractive index is greater than a refractive index n2 of the surrounding tubular carrier substance (outer optical fiber 5 c) for the divider device 6 . The divider 6 can also be made of glass or plastic, the actual divider 6 mechanically, for. B. can be introduced by scoring, cutting, milling, etc. Other methods for producing the divider device 6 are printing, in particular screen printing, with a rectangular cross section of the optical waveguide divider device 6 being more suitable. Thermal processes and laser processing allow particularly fine structures, comparable to those by etching or photographic methods, provided that the appropriate material is used, being carried out directly by exposure, development and fixing on the outer divider device 6 or subsequently as a film strip or scales printed on a film can be applied. For this purpose, the material is selected accordingly, restrictions being imposed only by the refractive index.

Divider devices 6 , which are present as a negative in a matrix, ie with a raised structure, appear particularly suitable for series production where there is supposed to be a recess in the divider device 6 itself. Fig. 7a shows such an embodiment. Here is in the negative form z. B. by injection molding process, material with the refractive index n2, for example PMMA (polymethyl methacrylate), is first introduced for the dividing device 6 , then the dye molecules 28, which are uniformly present in suitable plastic with n1 greater than n2. The arrangement can not only have round, as shown in Fig. 6, but also other cross sections, in particular rectangular (polygonal).

Fig. 7a shows a linear dividing means 6 according to the invention having a structure in which the surface with such a dividing means 6 and the fluorescent optical fiber 5 is present according to the shape described above as a single component.

The operation of the thus constructed linear portions device 6 is shown in detail in Figure 7a, and will be described in more detail below. Once the light from the light source 1, which is focused in accordance with incident on the dividing means 6, it always occurs in the core 5 b of the optical fiber 5 when it falls through the slots 22 almost undisturbed. Here the light falls through the raised surface of the outer jacket. This incoming light is absorbed by the dye molecules 28 in the optical waveguide 5 , as a result of which the dye molecules in turn fluoresce immediately.

Delays due to the lifespan of the excited dye molecules (typically in the nanosecond range), scattering in the optical waveguide 5 (less than nanoseconds) and due to the propagation speed of the light (also in the nanosecond range) can be neglected in the applications here (typical time resolution in the microsecond range).

However, with strong attenuation of a plastic optical waveguide 5, the dependence of the amount of light registered on the photodetector 7 on the distance of the incident light or the light source / printhead arrangement, on the coordinate X in FIG. 7b, can be considerable. It is therefore better in such cases to mount the photodetectors 7 and 9 on both ends of the optical waveguide 5 , although in most applications a photodetector 7 is sufficient.

The light signals can of course be guided at both ends through further flexible optical fibers or fiber bundles to a common photodetector 7 .

However, if the arrangement shown in FIG. 7a is selected, then according to FIG. 7b, after addition 25 of the averaged output signals 26 and 27 of both photodetectors 7 and 9, an approximately constant signal 25 results regardless of the respective scanning position X.

It goes without saying for the person skilled in the art that, of course, with sufficiently large attenuation of the optical waveguide 5, the scanning position itself can be determined from the difference between the two photodetector signals and / or the output signals 26 and 27 , which is in principle independent of a dividing device 6 . In such a case, the latter can be dispensed with.

Finally, from the increase or decrease in the output signals 26 and 27, a conclusion can be drawn about a movement in one of the two possible directions of movement of the print head 2 .

A divider device 6 according to FIGS. 8a and 8b serves the same purpose. Here, the slots 22 of the shape shown are introduced into the dividing device 6 . In such a case, the scanning light profile 29 of the light source 1 has the profile shape shown in broken lines in the plane of the dividing device 6 . A simple diaphragm and a cylindrical lens 31 in front of the light source 1 serve this purpose. In such a case, an output signal 30 of the photodetectors 7 and 9 runs at the output signal level 30 a shown in the lower part of FIG. 8 b, the output level 6 c initially being maximum and then falling approximately to half the value (stage 6 b), if the printhead 2 with the light source 1 runs from left to right over the divider device 6 - and only half the amplitude followed by the full amplitude, occurs when the printhead 2 with the light source 1 moves from right to left along the divider device 6 .

In summary, it can be stated that by using the simplest linear divider devices 6 according to the invention, the position determination and control of print heads or read / write heads in printers or similar office equipment can be manufactured with a simple construction, few components and low manufacturing costs compared to the advantages described the known facilities.

Reference list

1 light source
2 printhead
3 voucher
4 light beam
4 a light source profile
5 fiber optic cables
5 a end of fiber optic
5 b core of the FO
5 c outer fiber
6 divider device
6 a mask
6 b level
6 c output level
6 d half value
7 photo detector
8 optical filters
9 photo detector
10 axis of movement
11 assigned
12 Print head drive
13
14
15
16
17 Drive electronics
18th
19 Light source supply
20 evaluation electronics
21 mirrors
22 slot
23 footbridge
24 output signal photodetector
25 Sum of the average detector signals
26 Averaged output signal of the photodetector 7, 27 26 a Averaged output signal of the phototector 9
28 dye molecule
29 scanning light profile
30 output signal
30 a output signal level
31 lens

Claims (16)

1. A method for determining the position of a moving print head or read head, in particular in an office device, within a print or read line, in which measurement signals are generated on an optically scanned scale and used to trigger a print or read process, characterized in that that a light source ( 1 ) is moved together with the print head ( 2 ), that the focused light of the light source ( 1 ) is directed via an optical deflection by total reflection along the movement axis ( 10 ) onto at least one photodetector ( 7 ; 9 ) and that the respective position of the print or read head is determined in evaluation electronics by changing the signal of the light pulses. 2. The method according to claim 1, characterized, that when evaluating the pulses for the respective position of the Print or read head in connection with a simultaneous Time recording also the speed and acceleration of the respective printing or reading process is recorded. 3. The method according to any one of claims 1 or 2, characterized in that the light emitted by the light source ( 1 ) is changed into light of a different wavelength by entering an optical waveguide ( 5 ). 4. Device for controlling a reciprocable carriage, which carries a printhead and / or a reading head, with an optically scanned scale and a receiver for the measurement signal, which in an evaluation electronics for controlling the drive movement of a carriage motor and / or the actuation of the printing elements can be input, characterized in that a light source ( 1 ) can be moved together with the slide for the print head ( 2 ) or the read head, that the light source ( 1 ) is directed perpendicular to the axis of movement ( 10 ) of the slide and that focused light beams ( 3 ) can be reflected by deflecting means along the movement axis ( 10 ) onto at least one photodetector ( 7 ; 9 ), the output signals ( 30 ) of which can be switched to evaluation electronics. 5. Apparatus according to claim 4, characterized in that a dividing device ( 6 ) consisting of translucent and opaque sub-areas is arranged on the path of movement. 6. Device according to one of claims 4 or 5, characterized in that the light source ( 1 ) from a light-emitting diode (LED), a laser diode (LD) or a small incandescent lamp is formed. 7. Device according to one of claims 4 to 6, characterized in that the divider device ( 5 ) has a mask made of translucent and opaque, arranged in the direction of the axis of movement ( 10 ) and parallel to one extending in the direction of the axis of movement ( 10 ) Optical fiber ( 5 ) is arranged. 8. Device according to one of claims 4 to 7, characterized in that the deflecting means consists of a fluorescent optical waveguide ( 5 ) along the movement axis ( 10 ) of the print head ( 2 ), wherein typically fluorescent dye molecules in the optical waveguide ( 5 ) less, more uniform Concentration contained in an optically clear plastic or glass. 9. Device according to one of claims 4 to 8, characterized in that a photodetector ( 7 ) is assigned a narrow-band optical filter ( 8 ) which is transparent in the region of the fluorescence wavelength and directly on the ends ( 5 a) of the optical waveguide ( 5 ) is applied. 10. Device according to one of claims 4 to 9, characterized in that one end ( 5 a) of the optical waveguide ( 5 ) by means of a mirror ( 8 ) is completed. 11. Device according to one of claims 4 to 10, characterized in that the dividing device ( 6 ) is applied directly by mechanical, chemical or photographic means to the optical waveguide ( 5 ) in the direction of the axis of movement ( 10 ). 12. Device according to one of claims 4 to 11, characterized in that the fluorescent optical waveguide ( 5 ) is formed from two concentric cross-sectional areas of different refractive indices (n1, n2), such that the radially inner refractive index (n1) is greater than that radially outer refractive index (n2). 13. Device according to one of claims 4 to 12, characterized in that the optical waveguide ( 5 ) has a polygonal cross section, the divider device ( 6 ) being applied to one of the polygon surfaces. 14. Device according to one of claims 4 to 13, characterized in that on the optical waveguide ( 5 ) at least at one end ( 5 a) a further flexible optical waveguide or a fiber bundle of further optical waveguides is connected. 15. An apparatus according to any one of claims 4 to 14, characterized in that one has made a mask (6 a) existing dividing means (6) having one or more stages (6 b) provided with a slit shape having a slit width (6 d) outstanding light source profile ( 4 a) is opposite, so that the output signal ( 30 ) is also present in steps. 16. Device according to one of claims 4 to 15, characterized in that the optical waveguide ( 5 ) is alternately axially composed of doped disks made of fluorescent material and undoped sheets, that is to say of crystal-clear material.