JPS6123465A - Drum type scanner - Google Patents

Abstract

PURPOSE:To attain high accuracy of picture element positioning by providing a rotary encoder incorporatedly with a follower means. CONSTITUTION:A gear 16 is provided incorporatedly onto the shaft of a drum 11 as a drive means rotated incorporatedly with a rotary drum 11. Further, a gear 17 is provided freely rotatably as a follower means to a frame 15 meshing directly with the gear 16. The number of teeth of the gear is selected less than those of the gear 16. The gear 17 is provided with a flange 20, and a pulse generating disc 22 constituting a rotary encoder 21 is fitted to the flange 20 and a photoelectric converting pulse generating circuit 23 of the rotary encoder 21 is fitted to the frame 15. Thus, highly accurate picture element position is attained by using the rotary encoder with small size and simple constitution in this way.

Description

[Detailed description of the invention] (Technical field) The present invention relates to a drum type scanning device.

(Prior Art) A drum-type scanning device having a rotating drum and a scanning head is used to scan images such as facsimile machines, printers, document reading tears, etc.
Widely used for reading and recording text information. There are two types of drum-type scanning devices: one in which the scanning head moves in the axial direction of the rotating drum, and the other in which the scanning head consisting of multiple elements extends and is fixed in the axial direction of the rotating drum. In both types, a write signal is sent to the scanning head or a read signal is extracted from the scanning head in accordance with the rotation of the rotating drum. In such a drum-type scanning device, if the rotational speed of the rotating drum is uniform when evaluated with pixel-by-pixel accuracy, the scanning head signal, that is, the write signal and read signal, is a signal that corresponds to a temporally linear positional relationship. There is no problem in processing it as such.

Therefore, as a conventional facsimile scanning device, for example, 8
A device has been proposed in which a rotary drum is stably rotated at a constant low speed using a multi-pole motor with ~16 poles. However, in this case, there is a drawback that the motor is large and the cost is high.

In addition, as another drum-type scanning device, a rotary encoder is directly connected to the rotating shaft of the rotating drum, and a signal is obtained from this rotary encoder every time the rotating drum rotates by a predetermined amount, for example, by a pixel unit amount to control the signal of the scanning head. Something like this has been proposed.

FIG. 2 shows a known example in which the signals of the scanning head are controlled by a rotary encoder as described above, and is described on page 28 of Vol. 25, No. 12 of Electronic Technology. This drum-type scanning device rotates a drum 1 in the direction of the arrow by a drive motor 2, and detects the rotational position by a rotary encoder 3 directly connected to the rotation shaft of the drum 1. Based on this detection signal, a step motor 4 is activated as shown by the arrow. It is adapted to control the operation of on-demand type inkjet color scanning heads 6, 7, 8 and 9 of black, cyan, magenta and yellow held on a rad carriage 5 for scanning which moves in the axial direction of the drum 1. .

In this way, it is extremely common to read the rotation of the drum using a rotary encoder directly connected to the drum.
It is often used with a pixel density of 11m, and even when scanning the short side of A4 size 210n+m, the pixel density is 1680~3m.
Since the number of pixels is 360, the rotary encoder has the disadvantage of being large and expensive, and this disadvantage becomes even more severe when recording or reading a larger screen.

OBJECTS OF THE INVENTION An object of the present invention is to eliminate the above-mentioned drawbacks and to provide a drum-type scanning device suitably constructed so that a desired pixel accuracy can be obtained using a simple and compact rotary encoder.

(Summary of the Invention) In the present invention, a driven means is rotated at a faster rotation speed than the rotating drum by a driving means that rotates integrally with the rotary drum, and a rotary encoder is provided integrally with the driven means. A small and simple rotary encoder with a small number of pulses per rotation is used to obtain a desired number of pulses per rotation of the drum, thereby obtaining a desired pixel position accuracy.

(Embodiment) FIGS. 1A and 1B show an embodiment of the present invention, in which FIG. 1A shows a sectional view, and FIG. 1B shows a left side view of FIG. 1A. The rotating drum 11 is constructed by integrating a hollow cylinder 12 and a flange 13, is supported by a frame 15 via a bearing 14, and is rotated in a predetermined direction by a drive motor (not shown). This rotating drum 11
A gear 16 is coaxially and integrally provided as a driving means. Further, a gear 17 is rotatably provided on the frame 15 as a driven means, directly meshing with the gear 16. This gear 17 has a smaller number of teeth than the gear 16, and is supported by a rotation support shaft 18 provided on the frame 15 via a bearing 19. This gear 17 is provided with a 7-flange 20, a pulse generation disk 22 constituting the rotary encoder 21 is attached to this flange 20, and a photoelectric conversion pulse generation circuit section 23 of the rotary encoder 21 that cooperates with this pulse generation disk 22 is attached to the frame. Install it on 15.

The main points of the configuration shown in FIG. 1 are to rotate the rotary encoder at high speed in conjunction with the rotation of the rotating drum;
The rotary encoder is configured to follow and rotate the rotating drum with high accuracy. In order to satisfy the former requirement, parameters specific to the power transmission means, such as drive and driven gear ratios, roller diameter ratio, sprocket tooth number ratio, etc., may be selected. In other words, it is easy to obtain a small and simple rotary encoder with a pulse number of usually less than a few hundred pulses per revolution, but the number of pulses required by a scanning device is more than a few thousand pulses per revolution of a rotating drum. Therefore, parameters specific to the power transmission means are set so as to obtain a rotational speed ratio corresponding to this ratio. Increasing the rotation speed ratio larger than this will bring about design difficulties, so it is recommended not to increase the rotation speed ratio too much by using a method that simplifies the process using electrical auxiliary means. It is preferable to do so. An example of this electrical auxiliary means is to obtain pulses from a rotary encoder at a rate of one per pixel and electrically generate interpolated pulses based on the pulses to control the scanning head signal. There is a structure.

Furthermore, in order to satisfy the latter requirement of transmitting the rotation of the rotating drum to the rotary encoder with high accuracy, it is a good idea to reduce the load and inertia on the driven side as much as possible. Therefore, a configuration in which a rotary encoder is provided in a power transmission system for driving a rotating drum is inappropriate because it results in a power transmission system with a heavy load and large inertia. Therefore, in the present invention, in order to reduce the load and inertia on the driven side, only the rotary encoder is rotated on the driven side. Furthermore, in order not to increase the load or inertia on the driven side, and to prevent the occurrence of uneven drive due to rotation transmission means such as gears, it is preferable to directly connect the drive means integrally attached to the rotating drum. A driven means integral with the rotary encoder is provided in contact with the rotary encoder. Here, if the driving and driven means are gears 16 and 17 as shown in FIG.
It is preferable to use helical gears or the like instead of spur gears for these gears 16 and 17.

In image processing devices such as printers and document scanners, when pixels located at the same position on adjacent scanning lines shift, the shift is noticeable, but continuous fluctuations over long periods in the direction of drum rotation are less noticeable. There is. In order to suppress such deviations between pixels located at the same position on adjacent scanning lines, the driving and driven means should be configured so that the rotational speed of the rotary encoder is an integral multiple of the rotational speed of the rotating drum. is valid. 0
□3□ and ffBt. □, 6□, In Fig. 1, Fig. 3A shows the pitch zaatar circle of the gear 16- as the driving means and the gear 17' as the driven means.
The diameter of gear 16- is an integral multiple of the diameter of
The drive side gear 16' and the driven side gear 17- directly mesh with each other so that the relationship shown by the line segments indicated by arrows is maintained. That is, the driven gear 17
'The point indicated by a above is B' of the drive side gear 16',
Corresponding to BH, B/JJ, this positional relationship will not collapse no matter how many times both gears 16=, 17' rotate. FIG. 3B is an expanded view of the scanned area on the rotating drum 11, showing points +, 7', and a/# corresponding to the above-mentioned line segment and the eight points. When the rotating drum 11 rotates multiple times and the scanning head moves, the trajectory created by a-, JJ, and ahJ becomes a dotted line in a direction parallel to the rotating drum axis. The pulses specifying the positions of a-, II, B/# are obtained based on the signals from the rotary encoder, and each time the rotating drum 11 rotates, the pulses specifying the positions of a"", aLJ
.

Since the gear 17-, which is integrated with the rotary encoder, and the gear 16-, which is integrated with the rotating drum 11, are engaged at the same tooth position every time when the position signal corresponding to a'' is sent out, there is no disturbance in the tooth profile. Even if the rotary encoder makes a speed-changing movement, or if the gears 16" and 17- are eccentric due to a problem with the machining or installation, the a', The signals indicating the positions of aH and a/II will be emitted exactly at a constant position on the rotating drum 11 each time.

Therefore, pixel positional deviation between adjacent scanning lines can be prevented with high precision.

In order to accurately transmit rotation from the rotating drum to the rotary encoder, a transmission mechanism without backlash is required. When gears, which are the most common type of rotation transmission means, are used, eccentricity occurs during gear processing and installation.1.It is difficult to create a state with no eccentricity at all, and it is difficult to create a state with no eccentricity at all, and it is difficult to create a state with no eccentricity at all, and It is unavoidable that the gears will wear out and backlash will occur due to the use of the gears. In order to prevent a decrease in the accuracy of rotational position transmission from the rotating drum to the rotary encoder due to such backlash, the gear as a driving means and the gear as a driven means should be installed in the direction where the distance between their axes becomes shorter. It is preferable to force them to engage with each other.

FIG. 4 shows such an embodiment, and the same reference numerals as those shown in FIG. 1 represent components having the same function. In this example, the frame 15 that supports the rotating drum and the frame 24 that supports the rotary encoder 21 are separated and constructed as separate bodies. The frame 24 is rotatably supported at one end by a pin 25 with respect to the frame 15 that supports the rotating drum, and a pin or hole is provided at the other end of the frame 24 and a corresponding part of the frame 15, so that The frame 24 is biased in the direction of drawing the frame 24 toward the frame 15 by hanging the spring 26, thereby constantly biasing the gear 16 on the rotating drum side and the gear 17 integrated with the rotary encoder 21 in a direction that shortens the distance between the shafts. to strengthen With this configuration, even if both gears 16.17 are eccentric or worn, both gears 16.17 can always mesh without backlash. It is possible to effectively prevent a decrease in the accuracy of position transmission from the rotating drum to the rotary encoder 21 due to backlash.

Note that the present invention is not limited to the above-mentioned example, and can be modified or changed in many ways.

For example, in the above-mentioned example, the rotation of the rotating drum is transmitted to the rotary encoder by using gears as the driving means and the driven means and directly meshing these, but it is also possible to transmit the rotation using a belt or a timing belt. Alternatively, the transmission may be configured using friction rollers instead of gears.

(Effects of the Invention) As described above, according to the present invention, high-precision pixel positioning can be performed in a scanning device with a large number of pixels using a small and simple rotary encoder. By setting the rotational speed to an integral multiple of the rotational speed of the rotary drum, the positioning accuracy between pixels corresponding to the same position on adjacent scanning lines can be made extremely high. In addition, by using the driving means and the driven means as gears and urging them in a direction that shortens the distance between the shafts and directly meshing them, it is possible to effectively prevent a decrease in rotational position transmission accuracy due to backlash of gear A7. I can do it.

[Brief explanation of the drawing]

Figures 1A and B are sectional views and side views showing essential parts of an embodiment of the present invention, Figure 2 is a perspective view showing the configuration of a conventional drum-type scanning device, and Figures 3A and B are in accordance with the present invention. Diagram for explaining another embodiment. FIG. 4 is a diagram showing a main part of still another embodiment. 11... Rotating drum 12... Hollow cylinder 13.
...Flange 14...Bearing 15...
Frame 16.16', 17.17-...
Gear 18...Rotation support shaft 19...Bearing 20...Flange 21...Rotary encoder 22...Pulse generation disk 23...Photoelectric conversion pulse generation circuit section 24...Frame 25... Pin 26...
spring.

Claims (1)

[Claims] 1. A drum-type scanning device in which the rotational position of the rotating drum is detected by a rotary encoder, and based on this detection signal, the signal of the scanning head facing the rotating drum is controlled pixel by pixel, A driving means that rotates integrally with the rotating drum is provided, a driven means that follows the rotation of the driving means and rotates at a faster rotational speed than the rotating drum, and the rotary encoder is provided integrally with the driven means. A drum-type scanning device characterized by: 2. The drum type scanning device according to claim 1, wherein the driving means and the driven means are configured such that the rotational speed of the rotary encoder is an integral multiple of the rotational speed of the rotary drum. Device. 3. The driving means and the driven means each include gears, and these gears are biased in a direction that shortens the distance between the shafts so as to directly mesh with each other. The drum type scanning device described.