JP3306145B2 - Feeder - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lead screw which is driven to rotate and a feeder which moves a moving body using a female screw member screwed to the lead screw. The present invention relates to a feed device for correcting the unevenness of the advance speed of the female screw member with respect to the feeding device.

[0002]

2. Description of the Related Art An image scanner for obtaining image information of a document or the like has a sub-scanning device for moving an image sensor in a direction (sub-scanning direction) orthogonal to a direction in which light receiving portions are arranged (main scanning direction). are doing. A ball screw is generally used for a feed device such as a sub-scanning device. A ball screw is inserted between a lead screw and a female screw member, and the steel ball is moved by rotating the lead screw. It is configured to linearly move a member to reciprocate a carriage such as an image sensor.

Incidentally, the lead accuracy of a ball screw is J
It is defined in the IS, one of which is the cumulative lead. FIG. 6 is a cumulative lead characteristic diagram of the ball screw, in which the vertical axis represents the amount of advance of the female screw member and the horizontal axis represents the lead rotation angle of the lead screw. In FIG. 6, a straight line I1 indicated by a chain line is a cumulative lead corresponding to the effective length of the screw portion of the lead screw. When the lead screw having the cumulative lead rotates, the lead screw is screwed to the lead screw via a steel ball. The movement of the female screw member fluctuates in a sine curve shape as indicated by a solid line with reference to the cumulative lead mainly due to mechanical strain generated in the lead of the threaded portion. That is,
While the lead screw makes one rotation and the female screw member advances by one pitch of the screw lead, unevenness in the advancing speed (this is called random walking) occurs. The cause of such a random walk error is that the ball screw used in the feeder of the machine for processing the lead screw has a random walk error, which is directly reflected on the lead screw to be processed. is there.

Therefore, when a ball screw having such a random walk error is used in a sub-scanning device that scans a line sensor of an image scanner, the random motion of the ball screw is directly reflected in the sub-scan of the image sensor, and the image is scanned. There is a problem that image unevenness occurs in the image due to speed unevenness in the sub-scanning direction at the time of reading, and image quality deteriorates. In order to solve the above-mentioned problem, it is conceivable to use a high-precision ball screw having a small random walking error.However, since such a ball screw is expensive, equipment including an image sensor increases cost. Problem.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems, and is directed to a lead screw having a random walking error.
It is an object of the present invention to provide a feeder capable of moving a female screw member linearly moved by the lead screw at a constant speed.

[0006]

In order to achieve the above object, the present invention provides a lead screw rotatably disposed, a drive motor for driving the lead screw for rotation,
A female screw member that is screwed to the lead screw and linearly moves by rotation of the lead screw, and is provided between the lead screw and the drive motor, and rotates the drive motor.
A rotation transmitting element for converting the random rotation of the female screw member generated by the lead pitch of the lead screw into unequal-speed rotation of the opposite phase and transmitting the rotation to the lead screw; A drive eccentric gear attached to the rotating shaft of the motor; and a driven eccentric gear attached to the lead screw and meshing with the drive eccentric gear, wherein the drive eccentric gear and the driven eccentric gear have the same pitch circle. Wherein the drive eccentric gear and the driven eccentric gear are aligned with each other such that a minimum radius portion of the drive eccentric gear and a maximum radius portion of the driven eccentric gear mesh with each other. Also, the present invention
The eccentric amount of the drive eccentric gear and the eccentric amount of the driven eccentric gear are made equal.

[0007]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram when the feeding device of the present invention is applied to an image input unit of an image scanner, and FIG. 2 is a schematic configuration diagram of an image sensor applied to the image scanner.

In FIG. 1, reference numeral 1 denotes a housing which covers the entire optical image reading section. In the housing 1, a pair of guide bars 2 extending in one direction are arranged in parallel at a predetermined distance from each other. A carriage 3, which is a moving body, is supported on the bar 2 so as to be movable along the longitudinal direction of the guide bar 2, and a close contact type image sensor unit 4 is installed on the carriage 3.

As shown in FIG. 2, the image sensor unit 4 has a rectangular parallelepiped casing 4a having a dustproof structure, a transparent glass 4b provided so as to cover an upper opening of the casing 4a, and a casing 4a. 1
A linear LED light source 4c for illuminating a document (not shown) disposed on an upper surface of a transparent glass (not shown) fitted in a document window 8 formed on the upper surface of the document, and a document image illuminated by the LED light source 4c And a light receiving section 4f composed of CCD chips arranged in a straight line via a ceramic substrate 4e at the focal position of the converging rod lens array 4d. Part 4
and a driving circuit 4g for driving the CCD chip of f. The rod lens array 4d and the light receiving section 4f
May be provided in a plurality of rows.

In FIG. 1, reference numeral 5 denotes a ball screw for linearly moving the carriage 3 along the guide bar 2. The ball screw 5 includes a lead screw 5a disposed in parallel with the guide bar 2 and rotatably, and a lead screw 5a. Lead screw 5
a and a female screw member 5b screwed via a steel ball (not shown), and the female screw member 5b is fixed to the carriage 3.

In FIG. 1, reference numeral 6 denotes a DC motor for rotating and driving a lead screw 5a.
a and one end of the lead screw 5a are connected by a rotation transmitting element 7 that converts the constant speed rotation of the DC motor 6 into a non-constant speed rotation of a phase opposite to the random walking characteristic of the female screw member 5b generated at one lead pitch of the lead screw 5a. ing. The rotation transmitting element 7 includes a drive eccentric gear 7a eccentrically mounted on the rotation shaft of the DC motor 6 and a driven eccentric gear 7b meshed with the drive eccentric gear 7a and eccentrically mounted on one end of the lead screw 5a. And these two eccentric gears 7a, 7b
Are composed of spur gears having the same pitch circle. Reference numeral 9 denotes a document holder that is attached to the upper surface of the housing 1 so as to be openable and closable.

Next, the operation of this embodiment configured as described above will be described. When the DC motor 6 is rotated at a constant speed by a speed command from a rotation control unit (not shown), the drive eccentric gear 7a attached to the rotating shaft 6a of the DC motor 6 is eccentrically rotated in the same direction, and the driven eccentric gear 7b
Is eccentrically rotated in a direction opposite to that of the drive eccentric gear 7a. Here, the gear center C1 of the drive eccentric gear 7a as shown in FIG.
Is the eccentricity from the rotation center O1 to the rotation center O1, and the pitch circle radius is r.
Then, the radius R1 of the eccentric gear 7a about the rotation center O1 is expressed by the following equation (1). R1 = (r ² −e ² sin ² θ1) ^1/2 −ecos θ1 (1)

If the eccentricity of the driven eccentric gear 7b from the gear center C2 to the rotation center O2 is e, and the pitch circle radius is r, the radius R2 of the eccentric gear 7b about the rotation center O2 is expressed by the following equation (2). It is represented by R2 = (r ² −e ² sin ² θ2) ^1/2 −ecos θ2 (2)

As is apparent from the fact that both the eccentricity of the drive eccentric gear 7a in the equation (1) and the eccentricity of the driven eccentric gear 7b in the equation (2) are indicated by the same symbol e. In this embodiment, the amount of eccentricity of the drive eccentric gear 7a is equal to the amount of eccentricity of the driven eccentric gear 7b. As is apparent from the equation (1), the radius R1 of the drive eccentric gear 7a changes depending on its rotation angle θ.
When a is rotated at a constant speed by the DC motor 6, the linear velocity of the drive eccentric gear 7a is minimum at R1 at the minimum radius and maximum at R1 at the maximum radius. Accordingly, the speed ratio of the driven eccentric gear 7b to the driven eccentric gear 7a becomes maximum when the largest radius portion of the driven eccentric gear 7a is meshed with the smallest radius portion of the driven eccentric gear 7b, and the opposite meshing is performed. At the minimum position, during which the speed of the driven eccentric gear 7b gradually decreases and increases. As a result, the rotation speed of the lead screw 5a including the driven eccentric gear 7b in one rotation cycle has a sine curve shape gradually decreasing in the negative and positive directions about the reference speed line I2 as shown by the solid line in FIG. Changes to

Therefore, due to the random walking of the female screw member 5b caused by the lead pitch of the lead screw 5a, the actual accumulated lead of the female screw member 5b shown by the solid line in FIG. 6 is changed to the standard female screw member 5b shown by the one-dot chain line in FIG. Cumulative lead I1
Point A in FIG. 6 where the difference exceeds
At the time point shown in FIG. 5, the DC motor 6 is operated in a state where the drive eccentric gear 7a and the driven eccentric gear 7b are aligned so that the minimum radius of the drive eccentric gear 7a and the maximum radius of the driven eccentric gear 7b mesh with each other. If it starts at a constant speed, the lead screw 5
As shown in FIG. 4, the rotational speed characteristic a of FIG. 4 has an antiphase relationship in which the random walk characteristic of FIG. 6 is shifted by 180 degrees, whereby the random walk of the ball screw 5 is canceled out, and the carriage including the female screw member 5b is provided. The advance speed of No. 3 is almost constant.

FIG. 5 shows the relationship between the lead rotation angle of the lead screw 5a and the amount of advance of the female screw member 5b at this time. As is apparent from FIG. , The feeding of the female screw member 5b substantially along the cumulative lead becomes possible.

In this embodiment as described above, the lead screw 5a and the rotating shaft 6a of the DC motor 6 are connected via the drive eccentric gear 7a and the driven eccentric gear 7b, and the eccentric gears 7a and 7b are used to connect the DC motor. Female screw member 5b which generates a constant speed rotation at a lead pitch of the lead screw 5a.
Since the configuration is such that the rotation is converted into unequal-speed rotation having a phase opposite to that of the random rotation and transmitted to the lead screw 5a, the female screw member 5b including the carriage 3 can be moved at a constant speed. Therefore, when the driving method of the lead screw 5a of the present embodiment is applied to the sub-scanning mechanism of the line sensor of the image scanner, even if a ball screw having a random walking error is used in the sub-scanning mechanism, the conventional method is used. Reading unevenness of the original image is reduced, and an image of image quality with less distortion can be obtained. Further, in this embodiment, since the random movement of the ball screw can be reduced only by assembling the eccentric gears 7a and 7b, the feeder can be provided at a low cost and can be easily added to the existing feeder. it can.

The feed mechanism using the lead screw of the present invention is not limited to the ball screw structure shown in the above embodiment. Further, in the above embodiment, the case where the rotation transmitting element is constituted by a pair of eccentric gears has been described, but the present invention is not limited to this, and an eccentric friction wheel or the like may be used.
Further, the amplitude of the speed characteristic when the lead screw is rotated at an irregular speed can be arbitrarily set by changing the amount of eccentricity e.

[0019]

As described above, according to the present invention,
In a feed device, the rotation of the drive motor is converted by the rotation transmission element into unequal-speed rotation of a phase opposite to that of the internal thread member generated at the lead pitch of the lead screw and transmitted to the lead screw, and the rotation transmission element is A drive eccentric gear attached to the rotating shaft of the drive motor, and a driven eccentric gear attached to the lead screw and meshing with the drive eccentric gear so that the drive eccentric gear and the driven eccentric gear have the same pitch circle. Since the driving eccentric gear and the driven eccentric gear are positioned so that the minimum radius portion of the driving eccentric gear and the maximum radius portion of the driven eccentric gear mesh with each other, the lead screw has a relatively large random walking error. However, the female screw member, which is linearly moved by the lead screw, can be moved with high precision at a constant speed. In the case of application can be a feed device capable of low quality readings distortion easily at low cost.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a configuration of an image scanner to which a feeding device of the present invention is applied.

FIG. 2 is a schematic configuration diagram of an image sensor used in the image scanner of the present embodiment.

FIG. 3 is an explanatory diagram of an eccentric gear in the present embodiment.

FIG. 4 is a rotational speed characteristic diagram of a lead screw obtained by the eccentric gear of the embodiment.

FIG. 5 is a graph showing the relationship between the lead rotation angle and the amount of advance of the female screw member at the time of random walk correction according to the embodiment.

FIG. 6 is a graph showing a relationship between a lead rotation angle of a ball screw and an advance amount of a female screw member.

[Explanation of symbols]

 Reference Signs List 5 ball screw 5a lead screw 5b female screw member 6 DC motor (drive motor) 7 rotation transmitting element 7a drive eccentric gear 7b driven eccentric gear

Claims (2)

(57) [Claims] A lead screw rotatably disposed; a drive motor for rotating the lead screw; a female screw member screwed into the lead screw and linearly moving by rotation of the lead screw; A rotation transmitting element that is provided between the drive motor and the drive motor and converts the rotation of the drive motor into a non-constant speed rotation having a phase opposite to that of a random walk of the female screw member caused by a lead pitch of the lead screw and transmitting the rotation to the lead screw. in feeding device provided with a preparative, the rotation transmitting element, Installing the rotary shaft of the driving motor
Drive eccentric gear and attached to the lead screw
And the driven eccentric gear meshing with the drive eccentric gear
Is composed, the said eccentric drive gear driven eccentric gear and the same pitch circle
A minimum radius portion of the drive eccentric gear and the driven eccentric
The drive eccentric gear so that the maximum radius of the gear meshes with the drive eccentric gear
The feed device , wherein the driven eccentric gear is aligned with the driven eccentric gear . 2. The eccentric amount of the drive eccentric gear and the driven eccentricity.
2. The eccentric amount of the gear is equalized.
Feeding device as described.