EP0782922A1

EP0782922A1 - Roller-printing rotary belt machine synchronization method and machine in accordance with this method

Info

Publication number: EP0782922A1
Application number: EP96203587A
Authority: EP
Inventors: Giorgio Sacchi
Original assignee: VIERO Srl
Current assignee: VIERO Srl
Priority date: 1995-12-19
Filing date: 1996-12-17
Publication date: 1997-07-09
Also published as: ITMI952666A1; IT1277288B1; BR9606084A; ITMI952666A0; KR970033845A

Abstract

Method for synchronization of the running of the belt and the rotation of the rollers in a printing machine with belt and rollers comprises the phases of creating a table containing the relative positions of a plurality of marks located along the belt, detecting the belt running by means of an encoder and synchronizing rotation of the rollers with the corresponding belt position information, detecting the sequential passage of said marks and correcting upon each mark detection the position information supplied by the encoder with the position memorized in the table for said mark. A machine in accordance with the present invention comprises a plurality of marks (13) arranged sequentially along a lateral edge of the belt to be detected by an optical sensor (14). When the sensor (14) detects passage of a mark the counting unit (17) of an encoder (16) is loaded with the position previously memorized in a memory (19) and corresponding to the true position of the detected mark (13).

Description

The present invention relates to a synchronization method for a rotary-belt printing machine for roller printing and a machine applying this method.
In printing machines with rotary belt and printing rollers it is important to supply accurate synchronization between the movements of the belt and printing rollers. In the prior art to achieve this there is usually a connection between the moving parts of the belt and the rotary heads or rollers.
This implies relatively high mechanical complexity of the machine and, because of the mechanical tolerances and wear and elasticity of the belt, the desired accuracy of synchronization is not always ensured.
In the prior art printing machines have been proposed with printing board and in which on the edge of the belt are applied marks and there is a sensor for detection of the position of the marks. Upon detection of a predetermined mark indicating a desired stopping position the sensor sends a stop signal to the machine and at the same time sends a zeroing signal to the counter of an encoder controlled by a wheel resting on the belt. In this manner the encoder counter supplies the stop error of the belt with respect to the desired position and permits adjustment of the stop position in feedback and by successive approximations. In known machines the presence of the sensor and wheel with encoder is thus utilized only to permit accurate stopping of the belt and does not supply any running synchronization with other moving parts. In such machines the position data contained in the encoder counter are usable only during belt movements at the low speeds typical of the stop phase. At higher speeds the possible slipping of the wheel makes the encoder counter unreliable in the long term (the desired accuracy being easily on the order of hundredths of a millimeter).
The general purpose of the present invention is to obviate the above mentioned shortcomings of the prior art machines by supplying an innovative method of synchronization of a rotary belt and printing rollers and a machine implementing this method.
In view of this purpose it is sought to provide in accordance with the present invention a method for synchronization of belt running with rollers rotation in a printing machine with belt and rollers and comprising the phases of creating a table containing relative positions of a plurality of marks located along the belt while detecting the belt running by means of an encoder and synchronizing the rotation of the rollers with the corresponding belt position information and detecting the sequential passage of the marks and upon each detection of a mark correcting the position information supplied by the encoder with the position memorized in the table for this mark.
In accordance with this method a rotary-belt printing machine comprising a powered rotary belt for running opposite the roller printing stations and comprising means of synchronization of the belt running and the roller rotation and characterized in that the synchronization means comprises a plurality of marks arranged sequentially along a side edge of the belt and an optical sensor arranged near this side edge and detecting the sequential passage of the marks and an encoder operated by the running of the belt and controlling a counting unit for sending belt position information and a roller rotation control unit synchronizing the rotation with the belt position information and a memory unit containing values corresponding to the relative position of the belt marks and a transfer unit controlled by a value of the table for transfer from the memory unit to the counting unit to reinitialize the count of the counting unit by that value and with the sensor sending to the transfer unit a control signal for transfer of a value corresponding to a mark upon detection of the passage of this mark.
To clarify the explanation of the innovative principles of the present invention and its advantages compared with the prior art there is described below with the aid of the annexed drawing a possible embodiment thereof by way of non-limiting example applying said principles.
With reference to the figure there is shown a partial diagrammatic view of a printing machine indicated generally by reference number 10 and having a rotary belt 11 for passing opposite successive roller printing machines (indicated diagramatically by reference number 12). The practical provision of such a machine is well known to those skilled in the art as are well known the structure and operation of printing stations so that they are not further represented or discussed herein.
Along one edge of the belt is applied a strip 13 bearing at intervals position stamps or marks made up of alternating light and dark areas arranged longitudinally to the belt. When the belt is running, an optical sensor or photoelectric cell 14 detects with the desired accuracy (for example centesimal) the passage under it of the transitions between light and dark areas.
Near the sensor is also located a small wheel 15 mounted on an encoder 16 and resting on the belt to detect the running movement of the latter.
The encoder 16 is connected to a counting unit 17 which counts the pulses produced by the encoder to supply at its output 18 an 'absolute' position of the belt on the basis of the rotation of the wheel 15.
A memory unit 19 possesses a correction table containing the positions of all the marks along the belt with respect to a predetermined mark.
Creation of the table can be done in various prior art ways. An advantageous way is to automatically acquire the position of each transition during an initial phase of calibration of the machine. This acquisition must be repeated with change of the belt or its stretching.
For automatic acquisition the belt is made to run at low speed to avoid slipping of the wheel and the encoder accurately measures the relative distance between transitions. With the passage of each transition under the sensor 14 the detection signal 22 produced by the sensor commands a transfer unit 21 which takes the count of the encoder and memorizes it in an orderly manner in the table.
As an alternative to the use of the encoder 16 there can be used a different expedient of the prior art consisting of mounting the sensor 14 on a powered slide (not shown) for accurate moving of the sensor longitudinally to the belt for a distance at least equal to the distance between two successive marks. During calibration the belt is made to run until the sensor detects a transition. Then the sensor is moved by the slide until it detects the next transition and a precision encoder located on the slide motor detects movement of the slide and supplies the value of the distance between the two transitions. By repeating this procedure for all the transitions there are obtained the true relative distances between each transition of the belt and there is created therefrom the correction table.
When the machine is running, each time the sensor detects passage of a mark, i.e. transition between light and dark, it sends a detection signal 22 to a loading unit 20 which takes from the unit 19 the absolute position value of that mark and loads it into the counting unit 17 to replace the value counted up to that moment by the encoder. The encoder then continues counting starting from the new value.
Essentially, upon passages of each transition under the detector the encoder is resynchronized with the belt to eliminate any error which might have been introduced in the count in the meantime, for example due to slipping of the measuring wheel on the belt. Since the distance between the marks is small with respect to the movements made by the belt at high speed (e.g. approximately 2.5 cm) the errors which can be made in the count between two transitions are virtually without affect.
Recognition of the particular transition for taking from the table the correct value associated therewith can be done simply by utilizing the sequentiality of transitions and values. In other words, upon starting of the machine there is recognized by any method of the prior art an initial mark and a running index of the table is initialized to point to the position value corresponding thereto. Upon each subsequent transition passing under the sensor the index is merely increased to point to the immediately following value in the table which is in the same sequential order as the marks on the belt and this value is loaded into the encoder counter.
The entire synchronized position detection system can be brought together in a position detection unit indicated generally in the figure by reference number 24. This detection unit can be implemented for example by means of an appropriately programmed microprocessor board as may be readily imagined by those skilled in the art.
Thanks to the principles of the present invention the output 18 of the position detection unit always supplies the exact belt position with only possible negligible fluctuations due to the loading of a new value in the counter upon each transition.
The position signal present at the output 18 is thus sent to control units 23 to control printing roller rotation.
Each control unit 23 has an encoder which detects the position of the associated roller. The control units can thus control rotation of the head to follow the true belt position indicated by the output 18. The control units 23 are essentially of the prior art and thus are not further discussed or shown.
Advantageously, to prevent electrical disturbances from altering the transmission of position information between the detection unit and the roller rotation control units the transmission can be followed by means of optical fibers 25 by using known electro-optical transceivers 26.
It is now clear that the preset purposes have been achieved by providing a printing machine in which perfect synchronization of the relative movements of the belt and printing heads with rotary rollers is ensured.
Synchronization of the heads with respect to the belt position instead of to its movement members (e.g. powered belt-rotating rollers) eliminates errors due to mechanical tolerances, play and elasticity of the belt. In addition the use of the solution in accordance with the present invention permits simplification of the structure of the machine mechanical transmissions. The continuous resynchronization of the detection encoder of the belt position prevents any significant error in measurement of said position.
Naturally the above description of an embodiment applying the innovative principles of the present invention is given by way of non-limiting example of said principles within the scope of the exclusive right claimed here.

Claims

Rotary-belt printing machine comprising a powered rotary belt (11) for running opposite roller printing stations (12) and comprising means for the synchronization of the belt running with the roller rotation and characterized in that said means comprise:
- a plurality of marks (13) arranged sequentially along a lateral edge of the belt,

- an optical sensor (14) arranged near said lateral edge and detecting the sequential passage of said marks (14),

- an encoder (16) operated by the running of the belt and controlling a counting unit (17) for the sending of belt position information,

- control unit (23) controlling rotation of the rollers while synchronizing rotation with said belt position information,

- a memory unit (19) containing values corresponding to the relative position of the belt marks (13);

- a unit (20) for controlled transfer of a value from the memory unit (19) to the counting unit (17) to reinitialize the count of the counting unit by said value,
with the sensor (14) sending to the transfer unit (20) a control signal for transfer of a value corresponding to a detection mark of the passage of said mark.
Machine in accordance with claim 1 and characterized in that the encoder (16) is operated by a wheel (15) arranged in contact with the belt surface.
Machine in accordance with claim 1 and characterized in that during a calibration phase means (14-17, 21) of detection of the relative position of the marks memorize the relative positions of the marks in said memory unit (19).
Machine in accordance with claim 3 and characterized in that the detection means comprises the encoder (16), the counting unit (17), the sensor (14) and a second unit (21) for transfer of the count from the counting unit (17) to the memory unit (19) upon detection of a mark (13) by the sensor (14).
Machine in accordance with claim 1 and characterized in that the position information is transmitted from the counting unit (17) to the control unit (23) through optical fiber cables (25).
Method for synchronization of the running of the belt and the roller rotation in a belt printing machine and comprising the phases of creating a table containing the relative positions of a plurality marks located along the belt, detecting the running of the belt by means of an encoder and synchronizing the roller rotation with the corresponding belt position information, detecting the sequential passage of said marks and upon each detection of a mark correcting the position information supplied by the encoder with the memorized position in the table for said mark.