JPH04251772A - Sheet thickness-detecting mechanism of impact printer - Google Patents

Abstract

PURPOSE:To improve accuracy of sheet thickness detection for a sheet thickness- detecting mechanism in which an encoder is mounted to a shaft of a pulse motor for driving an eccentric shaft that moves a carriage equipped with a print head up and down by making the ratio of the number of teeth of a pinion to the number of poles of the pulse motor integral one. CONSTITUTION:In a sheet thickness-detecting mechanism, the revolution of a pulse motor 1 is reduced by reduction gears 12, 13 and an eccentric shaft 4 is driven therewith for moving a carriage 5 and a head 6 up and down. Load applied to the pulse motor 1 is detected by variation in cycles of output signals from an encoder 9. The thickness of the sheet is recognized by taking the difference between the sheet and the surface position of a platen 7 that is measured beforehand. At this time, the number of poles of the pulse motor 1 is made 48 for one revolution, while the number of teeth of a pinion 8 attached to the pulse motor 1 is made 24. By making the ratio of the number of poles to the number of teeth integral one, the phase advancement by the phase change of the pulse motor 1 can be agreed in the ratio of 1:2 with the phase delay occurring in meshing of the gear, and thereby useless vibration can be restrained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a paper thickness detection mechanism for an impact printer.

0002

2. Description of the Related Art Generally, as shown in FIG. 3, a paper thickness detection mechanism controls the rotation of a pulse motor 1 by first reducing gear
A reduction gear 13 is used to reduce the speed, and the eccentric shaft 4 is rotated to move the carriage 5 and head 6 up and down. Then, the load applied to the pulse motor 1 is detected from the change in the period of the output signal of the encoder 9 by the method described later, and the load increase due to the tip of the head 6 coming into contact with the paper surface 10 is detected and measured first. The paper thickness is recognized by taking the difference between the surface position of the platen 7 and the paper thickness, and is used as a parameter when setting the platen gap.

The following equation (1) is used to convert the encoder output signal into a load.

0004

[Math 1]

n: Number of steps (n≧48) Tm: Pulse motor phase switching period Tsum: Load equivalent value Then, when Tsum exceeds a certain threshold level, it is determined that the paper surface has been detected, and the pulse motor 1 is immediately switched off.
stop rotating. In such a paper thickness detection mechanism,
Conventionally, the number of poles (number of steps) of the pulse motor 1 was 48 per rotation, and the number of teeth of the pinion gear 18 was 18.

[0006]

[Problems to be Solved by the Invention] In the above-mentioned conventional technology, load fluctuations due to the meshing between the pinion gear 18 and the reduction gear 12 have a considerable effect on the encoder output signal cycle, and have a negative effect on the accuracy of paper thickness detection. was.

That is, conventionally, the number of poles of the pulse motor 1 is 48, and the number of teeth of the pinion gear 18 is 18.
The ratio between the two was 1:2.66...so,
The phase advance due to phase switching of the pulse motor and the phase lag due to the meshing load of each gear tooth are 1: 2.6.
It was happening at a rate of 6... For this reason, the actual movement of the pulse motor 1 for phase switching causes complicated vibrations, which has an adverse effect on the accuracy of paper thickness detection.

The present invention is intended to solve these problems, and its purpose is to suppress the influence of load fluctuations due to gear meshing and improve the accuracy of paper thickness detection.

[0009]

[Means for Solving the Problems] The paper thickness detection mechanism of the present invention is characterized in that the ratio of the number of teeth of the pinion gear of the pulse motor to the number of poles of the pulse motor is an integer ratio.

0010

[Operation] By setting the ratio of the number of teeth of the pinion gear to the number of poles of the pulse motor to an integer ratio, vibrations caused by phase switching of the pulse motor and load fluctuations caused by gear engagement are matched.
It is possible to suppress unnecessary vibrations.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory diagram of a paper thickness detection mechanism according to an embodiment of the present invention, and its basic operation is the same as that explained in the prior art shown in FIG.

1 is a pulse motor, 2 is a first reduction gear,
3 is a second reduction gear, 4 is an eccentric shaft, 5 is a carriage, 6
is a head, and 7 is a platen.

The number of poles of the pulse motor 1 is 48 per rotation, and the number of teeth of the pinion gear 8 is 24. Therefore, the ratio between the number of teeth of pinion gear 8 and the number of steps of pulse motor 1 is 1:2.

[0014] By setting the ratio of the two to an integer ratio in this way, the phase advance due to phase switching of the pulse motor and the phase lag due to gear meshing match at a ratio of 1:2, and unnecessary vibrations are suppressed. Ru.

FIG. 2 shows the actual measured value of the encoder signal expressed by the formula (
1) and plotted the results, (
A) is the result for a pinion gear with 18 teeth, and (b) is the result for a pinion gear with 24 teeth.

Comparing the load fluctuations of the graph (b) for 24 teeth and the graph (a) for 18 teeth, it is clear that there is a difference in the way the vibrations occur in the idle running region up to the point where the teeth hit the paper. With the 18 teeth, large vibrations occurred irregularly, and if this occurred just before paper surface detection (peak), the position would shift, causing a decrease in accuracy.

On the other hand, in the case of 24 teeth, since the vibration is simple and the amplitude is small, the influence near the peak is small, and the influence on accuracy is also small.

[0018]

[Effects of the Invention] According to the present invention, the accuracy of paper thickness detection can be improved by suppressing unnecessary vibrations of the pulse motor, and the practical effects are high.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an embodiment of a paper thickness detection mechanism of the present invention.

FIG. 2 is a graph plotting the results of calculating the encoder signal period at the time of paper thickness detection using equation (1).

FIG. 3 is a perspective view showing a conventional mechanism.

[Explanation of symbols]

1 Pulse motor 2 Reduction gear 3 Reduction gear 4 Eccentric shaft 5 Carriage 6 Head 7 Platen 8 Pinion gear 9 Encoder 10 Paper

Claims (1)

[Claims] Claim 1: A print head, a carriage to which the print head is attached, an eccentric shaft for moving the carriage up and down, and a pulse motor for rotating the eccentric shaft.
In a paper thickness detection mechanism composed of a pinion gear and a reduction gear for decelerating the rotation of the pulse motor, and an encoder attached to the shaft of the pulse motor,
A paper thickness detection mechanism for an impact printer, characterized in that the ratio of the number of teeth of a pinion gear of a pulse motor to the number of poles of a pulse motor is an integer ratio.