JPS60234872A - Paper thickness detector for printer - Google Patents

Abstract

PURPOSE:To form a proper clearance between a printing paper and a printhead according to paper thickness by pressing a sensor comprising a pressure-sensitive conductive rubber on a printing paper to detect the thickness thereof based on the movement of the sensor when the voltage resistance reaches a predetermined reference value. CONSTITUTION:A sensor body 35 is made up of a pressure-sensitive conductive rubber whose own electric resistance decreases gradually from the state of insulation to conduction according to external pressure. The pressure-sensitive conductive rubber herein used shall be such that is formed as thin film by blending a silicone rubber with a specified amount of graphite. The pressure-sensitive conductive rubber is suitable for a printer with a printhead 30 adapted to heat to a high temperature because of little characteristic changes due to temperature. The thickness of a printing paper 11 is detected based on the movement of a sensor 39 when the electric resistance of the sensor body 35 reaches a certain reference value to alter the printing interval between the printhead 30 and the printing paper 11 properly according to the paper thickness. Thus, the printing interval can be maintained properly to assure a clear printing regardless of the paper thickness.

Description

Detailed Description of the Invention "Object of the Invention" Industrial Field of Application This invention relates to a printing device that prints on printing paper on a platen while moving a carriage on which a print head is mounted along a platen. It is related to.

2. Description of the Related Art Conventional printing devices include, for example, as shown in FIG.
With the printing paper 2 mounted on the platen 1, the detection piece of the potentiometer 4 on the carriage 3 is brought into contact with the printing paper 2, and the motor 5 on the carriage 3 is adjusted to the correct position based on the resistance value of the potentiometer 4. The pinion 6 and the rack 7 are rotated in either direction, and as the motor rotates, the pinion 6 and the rack 7 are rotated in either direction.
The print head 9 is driven in the direction toward or away from the platen 1 together with the support stand 8 via the support base 8, and the print gap between the platen 1 and the print head 9 is set according to the thickness of the print paper 2. There is something.

Problems to be Solved by the Invention However, in the conventional configuration described above, the potentiometer 4 is always in contact with the printing paper 2, which causes problems such as staining the printing paper 2 and causing problems in feeding the printing paper. There is.

Further, since the potentiometer is expensive, there is a problem in that the manufacturing cost of the detection device increases.

``Structure of the Invention'' Means for Solving the Problem The present invention has been made to solve the above-mentioned problems. The sensor is provided so as to be able to approach or separate from the platen, and by bringing the sensor into pressure contact with the printing paper, the paper thickness of the printing paper is detected based on the amount of movement of the sensor when the voltage resistance of the sensor reaches a certain reference value. That's what I do.

Effect With the above configuration, in this invention, the sensor is pressed against the printing paper only when detecting the paper thickness of the printing paper, and an appropriate printing gap is maintained between the print head and the printing paper during normal printing operation. is formed.

EXAMPLE An example embodying the present invention will be described below with reference to FIGS. 1 to 6. As shown in FIG. 1, a printing paper 1 is provided between the left and right side walls 10a and iob of the frame 10 of the printing device.
platen 12 made of prismatic metal for supporting
has been erected.

In front of the platen 12, through holes 13 and 14 are formed in the side walls 10a and 10b, respectively, so as to face each other, and an eccentric shaft support hole 1 is formed in the through holes 13 and 14, respectively.
A pair of left and right eccentric bodies 16 and 17 having a diameter of 1 and 5 are rotatably supported, and a guide shaft 18 extending parallel to the platen 12 is supported on both eccentric bodies 16 and 17 by one small-diameter support shaft at both ends thereof. They are fitted and fixed, and each eccentric body 16, 17 and the guide shaft 18 are integrated.

A driven gear 20 located concentrically with the eccentric body 16 is fixed to the right side surface of the right eccentric body 16, and a drive gear 21 that meshes with the driven gear 20 is provided on the right side of the right side wall 16a. Drive motor 22 consisting of a step motor
is installed.

Therefore, when the drive motor 22 is rotated in the forward or reverse direction, the drive gear 21. Each eccentric body 16.17 is integrally rotated via the guide shaft 18 on the same axis through the driven gear 20, and the guide shaft 1 is rotated by the eccentric action of each eccentric body 16.17.
8 is moved back and forth so as to approach and separate from the platen 12.

A reference position detection piece 23 is attached and fixed at the base end to the outer surface of the left eccentric body 17, and the left side wall 10b
A reference position detection sensor 24 consisting of a photosensor including a light emitting element and a light receiving element is attached to the outer surface of the reference position detecting sensor 24, and as the eccentric body rotates 170 times, the reference position detecting piece 23 moves between the light emitting and receiving elements of the reference position detecting sensor 24. When the optical path is blocked by passing through, the reference position detection sensor 24 outputs a detection signal.

A carriage 25 is inserted into and supported by the guide shaft 18 so as to be movable along the platen 12, and the carriage 25 is connected via an endless timing belt 27 and a pair of pulleys 28 (not shown) partially fixed to the lower surface of the carriage 25. It is moved along the platen 12 by a drive motor. The timing belt 27. Pulley 2
8 and a drive motor (not shown) constitute a carriage moving device 41 shown in FIG. Further, in front of the carriage 25, a guide rail 29 extending parallel to the guide shaft 18 is installed between both sides 110a and lQb, and a pair of upper and lower protruding pieces 26 are provided at the front end of the carriage 2.5. is provided in a protruding manner, and the carriage 25 is moved left and right along the guide shaft 18 and the guide rail 29 with the protruding piece 26 loosely fitted to the rear edge of the guide rail 29.

As shown in FIGS. 1 and 2, a print head 30 is mounted and fixed on the carriage 25, and on the left side of the tip of the print head 30, the upper surface of the carriage 25 has an L-shaped side surface. As shown in FIG. 4, a block body 32 is fixed to the side surface of the upright portion of the bracket 31 on the platen side.

Further, an adjustment screw 33 that extends back and forth so as to penetrate the block body 32 is screwed into the upright portion. A flat mounting portion 33a is integrally formed on the front side of the adjustment screw 33, and the mounting portion 33a includes a sensor body 35 and a pair of electrode plates 34a and 34b that sandwich the sensor body 35.
A detector 40 consisting of is fixed with adhesive.

A cap-shaped cover 36 that covers the detector 40 and the block body 32 is attached and fixed at the proximal end to the upright portion of the bracket 31, and the tip of the cover 36 has an opening that allows the detector 40 to enter. 36a is formed. A leaf spring 37 is clamped and fixed at its base end between the lower base end of the cover 36 and the block body 32, and its tip bent portion 38 is fitted onto the outer electrode plate 34b. There is. The outer surface of the bent portion 38 is the opening 36a.
It is arranged at a position that slightly protrudes toward the platen 12 side through
It is located between 2 and 2. In addition, the bending part 3
The protrusion ω of the outer surface of the print head 30 from the print head 30 is smaller than the gap required for printing by the print head 30, and the bent portion 38 does not become an obstacle during printing.

The sensor body 35 is made of pressure-sensitive conductive rubber whose electrical resistance gradually decreases from an insulating state to a conductive state in response to external pressure.The pressure-sensitive conductive rubber is made of silicone rubber with a predetermined amount of graphite. A compound formed into a thin film is used. Since this pressure-sensitive conductive rubber hardly changes its characteristics due to temperature, it is suitable for a printing device equipped with a print head 30 that becomes hot. Note that the detector 40. Adjustment screw 33. The plate spring 37, the cover 36, etc. constitute a pressure sensor 39, and the adjusting screw 33 and the plate spring 37 constitute an initial pressure applying means.

Based on the eccentric rotation of the guide shaft 18, the carriage 25 and the print head 30 as well as the pressure sensor 39
is moved in the direction approaching the platen 12, that is, backward, and when the bent portion 38 of the leaf spring 37 is pressed against the printing paper 11 on the platen 12, the detector 40 is compressed based on the pressing force, and the fifth Sensor body 3 as shown in the figure
The resistance value of 5 is designed to decrease.

Further, by rotating the adjustment screw 33, the detector 40 is pressed toward the bent portion 38 of the leaf spring 37, and the sensor body 35 is compressed between the electrode plates 34a and 34b, and its An initial pressure can be applied to the sensor body 35, and the pressure can be changed and set.

Next, the control circuit of this printing device will be explained according to FIG. 6. 42 is a central processing unit (CPU);
The reference position detection sensor 24 and the output terminal of the operational amplifier 43 are connected to U42, respectively. Further, the pressure-sensitive sensor 39 is connected between the power source and the inverting input terminal of the operational amplifier 43 via the electrode plates 34a and 34b, and the pressure-sensitive sensor 39 is connected between the power source and the non-inverting input terminal of the operational amplifier 43. A variable resistor 44 is connected to which the reference resistance value can be set according to the thickness of the printing paper 11. The CPU 42 includes the print head 30 and the drive motor 22.
and the carriage moving device 41 are connected, and print interval data corresponding to the paper thickness of various printing papers 11, interval data between the pressure-sensitive sensor 39 at the reference position and the platen 12, and the operation of the entire printing apparatus are transmitted. Read-only memory (ROM) that stores control programs, etc.
)45. Random access memory (RAM) for storing the rotation angle of the drive motor 22 when detecting paper thickness, etc.
46 are connected to each other.

Next, the operation of the printing device configured as described above will be explained. In this embodiment, an initial pressure F1 corresponding to the resistance value R1 shown in FIG. 5 is applied to the sensor body 35 based on the rotation operation of the adjusting screw 33 shown in FIG. Now, when you turn on the power to the printing device in this state, the CPU4
2 drives the carriage moving device 41 to move the print head 30
is placed at the home position shown in FIG. At the same time, the drive motor 22 is driven. As the drive motor 22 rotates, the drive gear 21. Immediately after the pair of eccentric bodies 16 and 17 and the guide shaft 18 are rotated together via the driven gear 20, and the reference position detection piece 23 on the left eccentric body 17 crosses the optical path of the reference position detection sensor 24. The rotation of the drive motor 22 is stopped. Thereby, the carriage 25 . The print head 30 and the pressure sensor 39 are arranged at a position furthest from the platen 12 depending on the shape of the eccentric 16.1.7.

When the printing paper 11 is mounted on the platen 12 in this state, its lower end is detected by a printing paper detection switch (not shown), and a paper detection signal is output from the switch. Then, the CPU 42 drives the drive motor 22 based on the paper detection signal. As the motor 22 rotates in the forward direction, the guide @ 18 is eccentrically rotated via the drive gear 20 etc., and the print head 30, pressure sensor 39 etc. are moved backward toward the platen 12 together with the guide shaft 18. . Accordingly, the leaf spring 37 of the pressure sensor 39
The folding portion 38 is pressed against the printing paper 11, and the folding portion 38 is pressed against the printing paper 11.
8 is displaced forward against the elastic force of the leaf spring 37, and pressure is applied to the sensor body 35.

Then, the performance amplifier 43 compares its own resistance value, which decreases based on the pressure applied to the sensor body 35, with a preset reference resistance value R2, and determines that the resistance value of the sensor body 35 has reached the reference resistance value R2. At times, a predetermined signal is
Output to U42.

It goes without saying that this reference resistance value R2 is larger than the resistance value R1 corresponding to the initial pressure F1. Based on this, the CPU 42 stops normal rotation of the drive motor 22, and calculates the rotation angle data of the drive motor 22 from the reference position, that is, the movement amount data of the pressure sensor 39, and temporarily stores it in the RAM 46. .

Next, the CPLJ42 selects the pressure sensitive sensor 39. which is stored in the ROM45. Interval data between platens 12 and RAM 46
The paper thickness of the printing paper 12 is calculated by comparing the movement amount data of the pressure-sensitive sensor 39 stored in . Then, depending on the paper thickness of the printing paper 11, the CPU 42 moves the print head 30 to a position at an appropriate distance from the surface of the printing paper 11 by rotating the drive motor 22 in the opposite direction by a required angle. let

As mentioned above, in this embodiment, the sensor body 3
Sensor 39 when the electrical resistance of 5 reaches a certain reference value
The paper thickness of the printing paper 11 can be detected based on the amount of movement of the printing paper 11, and the printing interval between the printing head 30 and the printing paper 11 can be appropriately changed according to the paper thickness to maintain an appropriate printing interval.
Clear printing is possible regardless of paper thickness. Furthermore, when the pressure sensor 39 is pressed against the printing paper 11, compressive strain is generated in the sensor body 35, but the amount of strain is very small, about Q, Q5 mm, so that printing is performed simultaneously with the pressure contact of the bending part 38. There is no possibility that the head 30 will come into contact with the printing paper 11.

Furthermore, in this embodiment, when the printing paper 11 is set on the platen 12 in a bent state, even if the detector 40 comes into contact with the printing paper 11, the initial pressure is set higher than the contact pressure. If the contact pressure is applied, the sensor body 35 will not be distorted by slight contact pressure.
This does not change its own electrical resistance. Therefore, the operation of the sensor main body 35 is stabilized, and there is no risk that the paper thickness detection operation of the printing paper 11 will be performed incorrectly. The thickness can be detected accurately.

Further, in this embodiment, the sensor main body 35 is compactly formed of a thin film-like pressure-sensitive conductive rubber, and
Since the structure for supporting the sensor body 35 can be made compact, the inertial mass of the entire carriage 25 can be made smaller than that of the conventional example, and therefore,
There is no need to use a motor with large torque to move the carriage 25 back and forth.

Effects of the Invention As detailed above, the present invention eliminates the need to keep the sensor in contact with the printing paper during normal printing operation.
It is possible to create an appropriate gap between the print paper and the print head depending on the paper thickness, which may cause dirt to adhere to the print paper or interfere with the feeding of the print paper, causing IC damage. It has the excellent effect of being free of blemishes.

[Brief explanation of the drawing]

FIG. 1 is a partially broken plan view of a printing device embodying the present invention, FIG. 2 is an enlarged cross-sectional view taken along line 8-8 in FIG.
Figure 3 is an enlarged sectional view taken along the line B-B of Figure 1, Figure 4 is an enlarged side sectional view showing the mounting configuration of the pressure sensor, Figure 5 is a characteristic diagram of the sensor body, and Figure 6 is printed information. The circuit diagram of the device, FIG. 7, is a perspective view showing a conventional example of the present invention. In the figure, 11 is printing paper, and 12 is a platen. 25 is a gear ridge, 30 is a print head, and 39 is a pressure sensor. Patent applicant Brother Industries, Ltd. Agent Patent attorney On 1) Hironobu Figure 4 Figure 5

Claims (1)

[Claims] 1. A carriage (25) on which a print head (30) is mounted;
) is moved along the platen (12) while printing on the printing m (11) on the platen (12). A sensor (39) is provided so as to be able to approach and separate from the platen (12), and by bringing the sensor (39) into pressure contact with the printing paper (11), the electrical resistance of the sensor (39) is brought to a certain reference value. A paper thickness detection device for a printing device, characterized in that the paper thickness of the printing paper (11) is detected based on the amount of movement of the sensor (39) when the pressure-sensitive conductive rubber reaches A paper thickness detection device for a printing device according to claim 1, characterized in that it is constructed by blending graphite with silicone rubber.