Method and system for improved sheet running control in a sheet-fed printing machine

Abstract

A method for computer-aided sheet running control in a sheet-fed printing machine includes, during a printing operation, using a measuring sensor to detect a printed sheet in the printing machine and using an activation sensor to initiate measuring performed by the measuring sensor by emitting an activation signal. The activation sensor is mechanically fixedly installed without adjustment, and temporal deviations of the activation signal are determined and compensated. A system for computer-aided sheet running control in a sheet-fed printing machine is also provided.

Claims

1. A method for computer-aided sheet running control in a sheet-fed printing machine, the method comprising: mechanically fixedly installing an activation sensor in the printing machine without adjustment; during a printing operation, using a measuring sensor to detect a printed sheet in the printing machine and using the activation sensor to emit an activation signal for initiating measuring performed by the measuring sensor; and determining and compensating for temporal deviations of the activation signal.

2. The method according to claim 1, which further comprises determining the temporal deviations of the activation signal by using a duration of the activation signal at a constant speed of the sheet-fed printing machine being scaled by a factor.

3. The method according to claim 2, which further comprises using a computer to detect a duration of the activation signal at a constant speed of the sheet-fed printing machine during a learning run being separate from a normal printing operation of the sheet-fed printing machine, at the constant speed of the sheet-fed printing machine.

4. The method according to claim 3, which further comprises using the computer to determine, during the printing operation of the sheet-fed printing machine, a current speed of the sheet-fed printing machine by forming a ratio between the detected duration of the activation signal at a constant speed in the learning run and a measured duration of the activation signal during the printing operation.

5. The method according to claim 4, which further comprises calculating the factor by using a ratio of the current speed of the sheet-fed printing machine during printing operation and the constant speed of the sheet-fed printing machine in the learning run being determined.

6. The method according to claim 5, which further comprises using the measuring sensor as a computer to determine and store the detected duration of the activation signal at the constant speed in the learning run and the measured duration of the activation signal during the printing operation.

7. The method according to claim 6, which further comprises using the measuring sensor to carry out the calculation of the factor by using stored durations of the activation signal at a constant speed in the learning run, the measured duration of the activation signal during the printing operation and the constant speed of the sheet-fed printing machine in the learning run.

8. The method according to claim 2, which further comprises determining the duration of the activation signal by using a time in which the activation sensor is active or not active during a sheet run being detected.

9. The method according to claim 2, which further comprises setting the constant speed of the sheet-fed printing machine to be so low that a scanning rate of the sensors and their electronic processing times do not influence the determination of the temporal deviations of the activation signal.

10. A system for computer-aided sheet running control in a sheet-fed printing machine, the system comprising a mechanically fixedly installed activation sensor and a measuring sensor used as a computer and operated by the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

(1) FIG. 1 is a fragmentary, diagrammatic, cross-sectional view of a prior art system including a sheet running sensor and an activation sensor;

(2) FIG. 2 is a cross-sectional view of the prior art system showing a wrong adjustment of the activation sensor;

(3) FIG. 3 is a cross-sectional view showing the calculation of the ultrasound transit time;

(4) FIG. 4 is an enlarged, cross-sectional view showing the activation sensor fixedly installed according to the invention;

(5) FIG. 5 is a diagram showing a square-wave signal generated by the activation sensor at the switching output;

(6) FIG. 6 is a diagram showing the ideal measuring point after the falling edge of the signal; and

(7) FIG. 7 is a diagram showing the provision of the ultrasound transit time.

DETAILED DESCRIPTION OF THE INVENTION

(8) Referring now in detail to the figures of the drawings, in which elements corresponding to one another are provided with the same reference signs, there is seen, as in the prior art, a system including an activation sensor 2 and a sheet-running measuring sensor 1a, 1b, controlled by a computer. The system used therein has two sensors, including an actual sheet running sensor 1a, 1b (referred to hereafter just as the measuring sensor), which detects an overhang of a sheet 7 in grippers, as well as an activation sensor 2 and a reflector 6 in the cylinder, at which the optical or ultrasound signal is reflected for measurement. Such a system is shown in FIG. 1. On one hand, the system provides for measuring 4 without a sheet 7, in which the signal is correspondingly reflected and it is consequently indicated that there is no printed sheet 7. On the other hand, measuring 3 with a sheet 7 is shown, where the signal is scattered by the sheet, so that the measuring indicates the presence of a printed sheet 7. In order to ensure that the system operates correctly, however, an absolutely correct setting of the activation sensor 2 is necessary. An indication of this is the correct measuring angle α.sub.0 5. The measuring sensor 1a, 1b directly or its control system is preferably used as the computer. It is however alternatively also possible to use an external computer 21, which then notifies the measuring sensor 1a, 1b of the necessary data.

(9) If there is an incorrect or wrong adjustment of the activation sensor 2, the measuring sensor 1a, 1b, configured either as an optical measuring sensor 1a or as an ultrasonic measuring sensor 1b, either sporadically does not detect any object 7 and stops the printing machine even though a sheet 7 is present, or the cylinder is always detected, and consequently a sheet 7 is detected, even when no sheet 7 is present. In the first case, the adjustment takes place in such a way that measuring 8 is carried out too early, at too small a measuring angle of α.sub.f. In the second case, measuring 9 is carried out too late, at too large a measuring angle α.sub.s 11, so that the reflector 6 is missed. The two cases are depicted in two parts of FIG. 2, with the too-early adjustment 8 on the left and the too-late adjustment 9 on the right.

(10) In the method according to the invention, the activation sensor 2 is fixedly installed in the printing machine, so that, with all of the tolerances occurring, a target 15, for example an incoming printed sheet 7, activates the activation sensor 2 before the ideal measuring point at a time 16. FIG. 4 shows an example of such a fixedly installed activation sensor 2. The activation sensor 2 then generates a square-wave signal 20 at a switching output by outputting: HIGH 18 if the target 16 is detected, and otherwise LOW 17. In FIG. 5, such a square-wave signal 20 is shown. Because of the premature activation, there is a constant angular difference Δα.sub.REF between the ideal measuring point at the time 16 and the falling edge of the activation signal. This angular difference Δα.sub.REF depends on the tolerances of the measuring sensor 1a, 1b, the sensor mount and the target 16, and is generally different from printing unit to printing unit.

(11) With a known machine speed, a temporal difference can be calculated from the angular difference:

(12) $\Delta T_{\mathrm{REF}}=\frac{{\mathrm{\Delta \alpha }}_{\mathrm{REF}}}{\omega },\left[T\right]=\mathrm{ms},\left[\omega \right]=\frac{°}{\mathrm{ms}}$

(13) In a learning run, this temporal difference ΔT.sub.REF is determined at a machine speed that is as slow as possible. The machine speed should be slow in order to ensure that the scanning rate of the measuring sensor 1a, 1b and electronic processing times are of little significance in comparison with the machine speed. FIG. 3 shows an example of the calculation of the ultrasound transit time of the measuring sensor 1b, on which the scanning rate of the measuring sensor 1b depends. In this learning run, it is also determined in the measuring sensor 1a, 1b how great the time period ΔT.sub.TARGET in which the activation sensor detects the target 16 is at this machine speed. The time periods ΔT.sub.TARGET and ΔT.sub.REF are persistently stored in the measuring sensor 1a, 1b.

(14) Both time periods scale in inverse proportion to the machine speed, i.e. if the machine speed changes by a factor r, the time period changes by 1/r. Therefore, at twice the machine speed, the time period is halved. As a result, the machine speed can be calculated and the ideal measuring point at the time 16 can be calculated in the measuring sensor 1a, 1b, i.e. the measuring sensor 1a, 1b can initiate the measuring at the ideal point in time independently of the machine speed. For this purpose, the measuring sensor 1a, 1b measures the length of the signal that is generated by the target 16 ΔT.sub.TARGET,ω1. As a result, the current machine speed can be determined by forming the ratio between the stored pulse width at the reference speed and the measured pulse width. After the falling edge of the signal 20, it is necessary to wait for the time period until the ideal measuring point at the time 16 before initiating the measuring. This time period corresponds to the stored time period for the reference speed scaled by the ratio of the current machine speed and the reference speed. The situation is represented in the following formulas:

(15) ${\omega }_1={\omega }_{\mathrm{REF}}\times \frac{\Delta T_{\mathrm{TARGET},\mathrm{REF}}}{\Delta T_{\mathrm{TARGET},\mathrm{\omega 1}}}$$\Delta T_{\mathrm{REF},\mathrm{\omega 1}}=\Delta T_{\mathrm{REF},\omega \mathrm{REF}}\times \frac{{\omega }_{\mathrm{REF}}}{\mathrm{\omega 1}}=\frac{\Delta T_{\mathrm{TARGET},\mathrm{\omega 1}}}{\Delta T_{\mathrm{TARGET},\mathrm{REF}}}\times \Delta T_{\mathrm{REF},\omega \mathrm{REF}}$

(16) FIG. 6 then shows the ideal measuring point at the time 16 dependent thereon after the falling edge of the signal 20.

(17) In an alternative embodiment, the calculation in the measuring sensor 1a, 1b may also be performed with a characteristic curve, i.e. a relationship of the length of the activation pulse and the ideal point in time of the measuring is transmitted in the form of a characteristic curve with interpolation points by the controller to the measuring sensor 1a, 1b during initialization. If the measuring sensor 1a, 1b measures an activation pulse that lies between two interpolation points, interpolation is correspondingly carried out linearly.

(18) In a further embodiment, it is also possible to communicate the machine speed to the measuring sensor 1a, 1b by the controller of the printing machine in the form of the computer 21, instead of calculating it in the measuring sensor 1a, 1b by measuring the pulse width. However, this would have the disadvantage that there would then be an additional communication between the measuring sensor 1a, 1b and the computer 21. Furthermore, the machine speed can change quickly, for example in the case of an emergency stop, so that the speed must be communicated often or a deviation occurs between the communicated speed and the actual speed. In the case of the preferred embodiment, the determination of the machine speed takes place by measuring the pulse width ΔT.sub.TARGET directly before the measuring, so that during the time period ΔT.sub.REF,ω1 the changing of the machine speed can be disregarded.

(19) Furthermore, in a further alternative variant of an embodiment it is also possible to measure the length of the LOW signal 17 and calculate the machine speed from it, instead of the length of the pulse, that is to say the duration, for which a HIGH signal 18 is present. Since, however, the HIGH signal 18 is present for a much shorter time, specifically only about 1% of the time, the measuring of the HIGH level is thus influenced less by changes of the machine speed.

(20) The advantages of the method according to the invention as compared with the prior art can be summarized as follows:

(21) 1. There is no longer any need for adjustment, as a result of improvement in robustness and availability of monitoring, less effort involved during installation and in the case of servicing.

(22) 2. Activation pulses that are shorter than a lower limit or longer than an upper limit can be discarded. In this case, no measuring is initiated. Such invalid durations of the activation pulse may indicate EMC disturbances or malfunctions of the activation sensor.
3. The ultrasound transit time is provided, as is shown in FIG. 3. In the prior art, the sheet running control is adjusted when the printing machine is at a standstill.

(23) This results in an error due to the transit time of the packet of ultrasound pulses being disregarded, in the case of an ultrasound measuring sensor 1b, with the error becoming all the greater as the machine speed becomes higher. This is so since the propagation speed of a packet of ultrasound pulses is much lower than the propagation of the light of an optical measuring sensor 1a. Therefore, at high machine speeds, the reflector 6 is still at the correct location at the point in time 12 of the activation of the ultrasonic measuring sensor 1b, whereas, at a time 13 when the packet of ultrasound pulses arrive at the reflector 6, the cylinder has already turned further, which results in too large a measuring angle α.sub.R 14. In the case of the method according to the invention, on the other hand, the ultrasound transit time is contained in the time period ΔT.sub.REF determined in the learning run. This results in a dead time, which as a constant time period ΔT.sub.US is not included in the scaling, but has to be provided for each measuring speed, i.e. the correct initiation of the measuring 19 must always take place earlier by ΔT.sub.US, since the printing machine reaches the ideal measuring point at the time 16 while disregarding the transit time. This is shown correspondingly in FIG. 7. The ultrasound transit time is known on the basis of the distance between the measuring sensor and the ultrasound reflector 6. The situation is depicted in the following formulas:

(24) $\Delta T_{\mathrm{REF},\mathrm{\omega 1}}=\Delta T_{\mathrm{REF},\omega \mathrm{REF}}-\Delta T_{\mathrm{us}}$$\Delta T_{R,\mathrm{\omega 1}}=\frac{\Delta T_{\mathrm{TARGET},\mathrm{\omega 1}}}{\Delta T_{\mathrm{TARGET},\omega \mathrm{REF}}}\times \Delta T_{R,\omega \mathrm{REF}}$

(25) The following is a summary list of reference numerals and the corresponding structure used in the above description of the invention: 1a optical sheet running sensor 1b ultrasonic sheet running sensor 2 activation sensor 3 measuring with sheet 4 measuring without sheet 5 measuring angle α.sub.0 6 reflector 7 printed sheet 8 measuring too early 9 measuring too late 10 too small a measuring angle α.sub.f 11 too large a measuring angle α.sub.s 12 point in time of activation 13 point in time of arrival of packet of ultrasound pulses 14 too large a measuring angle α.sub.R 15 target 16 ideal measuring point in time 17 LOW—no target detected 18 HIGH—target detected 19 initiation of measuring 20 square-wave/activation signal 21 computer