JPH02231344A - Paper form detecting device - Google Patents

Abstract

PURPOSE:To always hold a distance between paper forms and a print speed at respective constant values by constituting the title device with a light receiving element, first and second comparators and an exclusive OR circuit for receiving outputs of both the comparators abovementioned as its input and detecting a delay of detecting the front end of the paper form. CONSTITUTION:An exclusive OR circuit 9 obtains an output E2 (0:Low, 1:High), shown in a table, from outputs E1, E'2 of the first and second comparators 7, 8. That is, a signal of detection delay of the output E1 is output to the output E2. For instance, when a paper form 6 is placed on a conveying route between its maximum position dmax(d') and standard position dave(d) and in a case when the output E1 of the comparator 7 is L(0: paper form present) and the output E'2 of the comparator 8 is H(1: paper form front end, absent), the output E2 obtains H(1:) showing a detection delay existing. In the other case of the table, no detection delay exists. The paper feed timing is variably controlled in accordance with a time delay of detection of the paper form front end, so as to hold a distance between the paper forms at a constant value and hold a print speed at a constant value.

Description

Detailed Description of the Invention (Industrial Technical Field) The present invention relates to a paper detection device for controlling the presence or absence of paper and the feeding timing of pre-fed paper in paper feeding devices such as printers and copying machines. .

(Prior Art) Examples of the configuration of a paper feed detection device are shown in FIGS. 5 and 6. In the case of FIG. Direction of paper 6 is solid line (a)
Alternatively, the sheet is conveyed along the path indicated by the dotted line (b), and the reflective photosensor 5 detects the presence or absence of the sheet.

In addition, in the case of Fig. 6, the guide plates 3 and 4 are bent,
This is an example in which paper is transported along transport paths a and b. By the way, the presence or absence of paper 6 is detected by this reflective photosensor 5, but depending on the type of paper and the distance between the paper in the guide plate and the reflective photosensor, The output changes depending on d or the focal length of the reflective photosensor. Regarding paper types, for example, OHP paper, second original paper, and plain paper have different reflectance and transmittance. OHP
Since the reflectance of paper and 2M drawing paper is lower than that of plain paper, if the amount of light irradiated by the LED of the reflective photo sensor is the same, the amount of reflected light will be smaller for OHP paper and 2nd original drawing paper than for plain paper. Therefore, the collector output current of the reflective photosensor becomes smaller, and therefore its output voltage also becomes smaller. The output waveforms of the reflective photosensor shown in Figs. 7 and 8 are for plain paper (dotted chain line), OHP paper, and paper (actual 1lA) in Fig. 2M paper in the paper feed detection device of Figs. 5 and 6, respectively.
The following cases are shown below. Here, since the luminous intensity of light is inversely proportional to the square of the distance, as is well known, the collector output current IC changes depending on the distance dm between the paper and the reflective photosensor, as shown in FIG. In addition, the reflective photosensor has a focal length (d in Fig. 9).
=2m+), and at locations farther than this focal length,
The smaller the distance d, the collector output current ■. The larger the distance d, the smaller the collector output current IC. The opposite is true at locations closer than the focal length.

(Problem to be Solved by the Invention) When paper is conveyed using the paper feed detection device shown in FIGS. 5 and 6, the distance d between the paper 6 and the reflective photosensor 5 is not constant and always changes depending on the state of the paper. do. For example, the leading edge of thin paper or paper with back curls moves along the guide plate 4 as shown in the conveyance path in FIG.
Paper without back curl (paper with stiffness) is conveyed by two conveyance rollers 1 and 2 as shown in the conveyance path shown in FIG. 5b. As a result, the paper 6 passing through the transport path a is longer by the distance (Δd) than the paper 6 passing through the transport route b.
d+Δd). Looking at this from the distance d and the characteristics of the collector output current IC in Fig. 9, if the distance d increases by 1 mm, the collector output current will change. decreases by approximately 18%. In addition, when the conveyance path is bent as in the paper feed detection device shown in FIG. changes.

In the above, if the paper has a high reflectance and a large amount of reflected light, the change in distance will not be much of a problem.
If the paper has a low reflectance, the collector output current I of the reflective photosensor 5 is
C changes greatly depending on the distance d.

If the reference voltage for paper detection is Vl shown in FIG. ) occurs. When the comparator has one reference value as in the conventional paper detection device, there is a change in the distance between the paper and the reflective photosensor as described above, and in order to prevent the detection delay (Δt) of the leading edge of the paper, it is necessary to In Figure 8, the reference voltage v
3 to match the distance 11tcl is the largest, such as VC, or increase the sensitivity of the sensor. However, if the amount of change in the distance d is extremely large, the reference voltage value will be lowered too much or the sensor sensitivity will be increased too much, and on the other hand, the margin (M) against malfunction due to the influence of ambient light etc. will decrease. A problem occurs.

In addition, as another conventional example, an object position detection device (Japanese Patent Laid-Open No. 60-101
No. 01) has been proposed. This improves position detection accuracy, but the reference voltage values of the two light receiving sections are the same, and if paper with low reflectance is used and the amount of change in distance d from the sensor is large, the reference voltage value Methods such as lowering the sensor sensitivity or increasing the sensor sensitivity may be considered, but there is a risk that malfunctions may occur due to the effects of ambient light. In addition, a sheet presence/absence detection device using multiple photosensors and using one of them as a reference voltage (Japanese Patent Laid-Open No. 62-111
No. 5656), there is a problem with variations in the photo sensor and its level adjustment amplifier, and due to the influence of external light, etc.
If only one sensor is exposed to light, there is a risk of malfunction.

Next, considering the amount of paper feed, in the paper feed detection device shown in FIG.
The paper feeding timing is controlled based on the time when the leading edge of the paper reaches the paper. However, as mentioned above, if there is a delay in detecting the leading edge of the paper (Δ1) (Fig. 8), the time difference. The paper stop position is extended. In other words, the time becomes shorter. That is,
In Fig. 8, the decrease between classes due to the detection delay (Δt) is linear velocity x Δt. Then, if this decrease becomes large and the paper gap becomes zero, a jam occurs.

Also, even if the paper gap is not zero at the position where the paper is pre-fed (details will be explained later), if the linear speed of the print engine itself is slower than the linear speed of the paper feeder, the registration rollers may not be able to catch up. A minimum paper spacing is required. Note that the pre-feeding is performed by stopping the leading edge of the paper at the nip of the registration roller (not shown) and the nip of the transport roller 2, and then returning the paper to the nip of the registration roller (not shown). It is calculated by subtracting the length of the paper in the roller section, so the shorter the paper, the larger the paper gap. Therefore, when the linear speed is constant, the larger the paper distance, the fewer sheets are transported per unit time, and the printing speed becomes slower. Therefore, the paper is conveyed a little in advance to reduce the paper gap. Is this behavior called prefeed? You can increase printing speed. The present invention prevents jam occurrence in the above-mentioned conventional apparatus due to a decrease in the grade due to a detection delay (Δt) of the leading edge of the paper due to one reference voltage VB, and prevents jams caused by a decrease in the number of grades by using two or more different reference voltages V Even if the distance d between the reflective photosensor and the paper changes, the paper feeding timing of the pre-fed paper is changed in response to the detection delay time to keep the paper distance constant and the printing speed constant. The purpose is to maintain (Structure and operation) In order to achieve the above object, the present invention includes a light receiving element that receives the amount of reflected light from the paper being passed through, and a light receiving element that receives the output of the light receiving element as one input. A sheet of paper with the lowest reflectance, and at a distance between the sheet and the light-receiving element. a first comparator whose other input is a reference voltage VB, which is the output of the light receiving element including a margin when the paper is transported most stably; a second comparator whose other input is the reference voltage Vc having the received light output at the farthest distance; and an exclusive device which uses the outputs of the first and second comparators as inputs to detect a delay in paper leading edge detection. It is characterized by being composed of a logical OR circuit. In the present invention, when the paper is between the maximum position 11dmax on the layout and the reference position dave, and the first comparator output is paper present (Low level), the exclusive OR circuit is set to High. level, indicating a detection delay. On the other hand, if there is no paper and both the first and second comparators are at High level, or the paper is at the standard level 11d.
ave is transported closer to the reflective photo sensor and detected by the first comparator, and if both the first and second comparators are at Lov level, it indicates that there is no detection delay. Then, by varying the paper feeding timing according to the delay time of paper leading edge detection, the paper spacing is kept constant and the printing speed is kept constant. (Embodiment) FIG. 1 shows a circuit configuration diagram of an embodiment of the present invention. Reference numeral 5 denotes a reflective photosensor, which is composed of a light emitting diode (LED) 51 and a phototransistor 52. Reference numeral 7 designates a first comparator, and one input terminal (-) of the comparator receives the received light output from the phototransistor corresponding to the amount of reflected light from the paper. In addition, a reference voltage V is applied to the other input terminal (+) from a reference voltage source IO. This is because, as explained in FIG. 8 above, among the sheets of paper 6 passing through, the sheet with the lowest reflectance is the one that is attached to the conveyor rollers 1 and 2 shown in FIG. 6 (or FIG. 5).
The distance d between the paper and the reversible photosensor 5 when the paper is being transported in both directions (paper position 5 on transport path b!), that is, the distance d between the paper and the reversible photosensor 5 when the paper is being transported most stably with little variation in distance. It is set using the output of the phototransistor 52 as a reference and taking into account the margin M. 8 is a second comparator, one input terminal (-) of which receives the output of the phototransistor 52 of the reflective photosensor 5, which is input to the input terminal (1) of the first comparator 7. ．． Further, a reference voltage vc is applied from a reference voltage source 11 to the other input terminal (+). This is because, as explained in FIG. 8, the paper with the lowest reflectance among the paper sheets 6 passing through is the guide plate 3 shown in FIG. 6 (or FIG. 5).
4 (sheet position on transport path a), that is, the distance d' between the paper and the reflective photosensor 5 when the paper is transported farthest from the reflective photosensor 5. is set based on the output of the phototransistor 52 at . 9 is an EX-OR circuit which receives the output E1 of the first comparator 7 and the output E2' of the second comparator 8 and outputs the output E, (table). Next, the operation will be explained with reference to the flowchart in FIG. 3 for changing the paper feeding timing and the flowchart for canceling prefeed in FIG. In the reflective photosensor 5, when the power supply voltage vce is constant, the amount of light irradiated by the light emitting diode (LED) 51 is constant, and the amount of light incident on the phototransistor 52 is determined by the reflectance of the paper 6 and the amount of light between the paper 6 and the phototransistor 52. It changes depending on the distance d (or d'). The first comparator 7 detects the presence or absence of paper 6, and has one input terminal (1) connected to a phototransistor 5.
When there is an output from 2, to the other input terminal (+)? It is compared with the reference voltage value v1, and the paper 6 is transferred to the transport path a or b.
, the input voltage exceeds the reference voltage v1 and the output E1 (L
ow level). The presence or absence of paper is determined based on this output E■, and the output E1 becomes one input of the exclusive OR circuit 9. Moreover, in the second comparator 8,
It is assumed that the leading edge of the paper 6 is detected, and one input terminal (-
), when there is an output from the phototransistor 52, it is compared with the reference voltage Vc to the other input terminal (+), and the paper 6
is on the transport path a or b, the input voltage is equal to the reference voltage V
C and the output E. ' (Low level) and becomes the other input of the exclusive OR circuit 9. The exclusive OR circuit 9
are the outputs E, E2' of the first and second comparators 7 and 8, and the output E shown in the table of FIG. 1 ("0" is Low, "1"
is High). That is, the detection delay signal of the output E1 is output to the output E.

For example, if the paper is at the maximum position dmax(
distance d') and the standard position [dave (distance d),
The output E■ of the first comparator 7 is at a low level (11 0
'F paper present), the output E2' of the second comparator 8 is High.
In the case of h level ("1 '" paper leading edge missing), output E2 becomes high level ("1"), indicating that there is a detection delay. On the other hand, if there is no paper and both comparators 7 and 8 are at High level (“1” no paper), or if the paper 6 is in the standard position da
ve, and is detected by the first comparator 7,
Both comparators 7 and 8 are at low level (“0” paper present)
In each case, the output E2 becomes a low level (“0”), indicating that there is no detection delay. First, as shown in FIG. 3(a), the counting operation of the detection delay of the paper 6 is performed by the exclusive OR circuit 9 of FIG.
If there is (High level “1”) (YES in SX),
Set the detection delay flag (S2), increment the detection delay counter (S,), and store the count value of the detection delay counter in the detection delay register (S,).
If there is no paper detection delay (No in St), the detection delay flag is set (S,) and the detection delay counter is reset (S,).
6) To be done. Also, the paper feeding and conveyance in this case is shown in FIG. 3(b). If there is a detection delay in the state of feed flag = 1 (S1) (S1.) (detection delay flag = 1), the setting values of each paper feed motor, paper feed clutch, and transport clutch are delayed by the delay time. (T1=ON time of S4, T,=OF
F time). That is, the motor and each clutch are turned on with the feed counter = T (SZZ) (N < s - s),
Feed counter" T2 ('s?) motor,
Turn each clutch OFF (S,). In other words, ゛motor,
By slowing down the set value of each clutch to 81■, the timing of paper feeding will be delayed. Furthermore, in S11, the paper feeding timing is changed according to the detection delay of the leading edge of the paper, so that the paper spacing can always be kept constant. Next, the case of canceling prefeed will be described using the flowchart in Figure 4. In the same figure (a), it is determined that paper is detected and fed (High level of output E2 is ``1'' and CSxs is YES), and the detection delay counter value is an allowable detection delay to ensure the minimum required paper spacing. maximum time x
If it becomes larger than i, that is, the paper interval is the minimum required interval.
What if it gets smaller? Catch-up jams can be prevented by canceling the feed (setting the flag S.). Figure 4(b) shows the relationship between the pre-feed paper length and the ON/OFF operation of the paper feed clutch, and the feed flag =
1 (s!3), feed cancellation flag = 1 (S■)
is not a state, and the breech counter = T, (S
■) When the paper length is the prefeed paper standard value Z,
If it is smaller (SaS), prefeed is performed and the paper feed clutch is turned on (S2,). Also, when the prefeed counter is T, (S,.), the paper feed clutch is turned OFF.
F t, (s.x). Resetting the pre-feed clutch (S-Z) - Fig. 2 shows a circuit diagram of another embodiment of the present invention, in which two reflective photosensors 5, 5' are used,
One input terminal (1) of the first and second comparators 7 and 8, respectively
This is the case when inputting . This detects the presence or absence of paper and detects the detection delay using dedicated sensors 5 and 5', allowing for highly accurate and smooth paper feeding. (Effects of the Invention) As described above, in the present invention, two comparators having two different reference values input the amount of reflected light from the paper from a reflective photosensor to detect the presence or absence of paper in the paper transport path. signal (E8) indicating a detection delay and a signal (E8) indicating a detection delay.
, ), it is possible to reliably detect the presence or absence of paper and the delay in detection even if there are variations in the distance between the reflective photo sensor and the paper being transported and fed. Therefore, the paper feeding timing can be changed according to the detection delay time of the leading edge of the paper, and the paper spacing can always be kept constant. Additionally, if the paper spacing falls below the required minimum value, prefeeding will not be performed, thereby preventing catch-up jams.

[Brief explanation of the drawing]

1 and 2 are circuit configuration diagrams of each embodiment of the present invention,
Fig. 3 is a flowchart for changing the paper feeding timing in this embodiment, Fig. 4 is a flowchart for canceling prefeed in this embodiment, and Figs. 5 and 6 are layouts of each example of the paper conveyance path. 7 and 8 are the output waveform diagrams of the reflective photosensor in FIGS. 5 and 6, respectively. FIG. 9 is a diagram showing the relationship between the reference voltages vA, vl, and vc, and a graph showing the distance d between the reflective photosensor and paper and the characteristic graph of the reflective photosensor (collector current c). 1.2...Conveyance roller, 3,4...Guide plate, 5,5'...Reflection type photo sensor, 51...Light emitting diode (LED), 52...Phototransistor, 6... paper, 7...first comparator (output E
■), 8...Second comparator (output E,').
9...Exclusive OR (EX-OR) circuit (output E
2), 10... Reference voltage source VB, 11... Reference voltage source vc. Figure 2 Patent Applicant: Ricoh Co., Ltd. (0)

Claims (1)

[Claims] A light-receiving element that receives the amount of reflected light from the paper that is being passed, and a light-receiving element that receives the output of the light-receiving element as one of its inputs. A first comparator whose other input is a reference voltage V_B which is the output of the light receiving element including a margin when the paper is transported most stably at a distance from a second comparator whose other input is a reference voltage V_C having the light reception output at the farthest distance from the light receiving element; and a paper leading edge detection circuit whose inputs are the outputs of the first and second comparators. What is claimed is: 1. A paper detection device comprising an exclusive OR circuit for detecting a delay, and changing the paper feeding timing of pre-fed paper in accordance with the delay time.