JPS6315153B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a printhead drive method for reducing type selection time in a serial printer.

The printing speed of serial printers is about 20 characters/second for type bar type printers and 40 characters/second for servo type printers.
Although it takes about seconds, the applicant has developed a type selection method that further speeds up this process. This type selection method is described in Japanese Patent Application No. 52-55457 (see Japanese Patent Application Laid-open No. 53-141724) entitled “Type selection method for serial printers”.
Although detailed in the above, the summary is as follows.
In other words, the one that takes the least amount of time to rotate the print head and select the desired type is a bang-bang control in which the printer is accelerated with torque +T until 1/2 of the rotation time t, and then decelerated with torque -T. However, since this operates in a non-linear region, it is susceptible to load fluctuations and tends to cause excesses or deficiencies in the amount of rotation, so if you add time to correct this, the required time is not necessarily short. Therefore, even if the acceleration part is operated in a bang-bang manner, the deceleration and stopping part is made to perform linear operation, that is, deceleration that follows the speed command curve that gradually decreases to the stopping point, so that it is possible to stop at the desired point with no excess or deficiency. Type selection time can be shortened. The speed command curve has an initial value V corresponding to the distance from the current position of the print head to the desired print position expressed by the number of print characters M,
A staircase wave signal that decreases by V/n every time the character rotates one character interval thereafter is convenient, but if the speed command curve is stepped, the motor drive current will be disturbed at the step.
It becomes vibrating and cannot rotate smoothly. Therefore, in the above-mentioned application, a smoother circuit is inserted that connects each step part of the staircase wave at the oblique side to form a substantially uniform slope line as a whole, and eliminates the source of disturbance occurring in the motor drive current to achieve smooth deceleration and stop. has made it possible to shorten the type selection time.

However, this smoother circuit is relatively complex and increases costs. On the other hand, smoothing of the staircase wave is also possible by multi-stepping, and in the method developed earlier, the staircase wave is smoothed once for each cycle of the position detector output, which is one cycle for each character interval. However, since the output of the detector is a sine wave and has two peaks, positive and negative, if each of these peaks is decreased by a certain amount, the number of steps in the staircase wave will double, and the step difference will be reduced. can be reduced to 1/2 and can be smoothed very easily.

The present invention focuses on such points, and its characteristics include a motor that rotationally drives the print head, and a detector that outputs a position signal indicating a change of one cycle per one character interval of the print head. , a stepwise signal having an initial value corresponding to the number of characters to be printed from the current position of the print head, and decreasing by a constant value by the output of the detector each time the character head rotates by a character interval; and the position signal. A method for driving a print head mechanism of a serial printer comprising an amplifier inputted with a speed voltage signal of the print head obtained by frequency-voltage conversion of the speed voltage signal of the print head and outputting a difference signal between the output position signals of the detector. The point is to generate a position pulse at each negative peak, double the number of steps in the step-like signal, and reduce the step difference to 1/2 to smooth the step-like signal. This will be explained in detail below with reference to the drawings.

FIG. 1 shows an overview of the print head drive section of a serial printer and is disclosed in the above-mentioned application.
1 is the print head, with 64 characters each in the upper and lower rows, total.
The 128 type letters are arranged in a crown shape. Reference numeral 2 represents a motor for rotationally driving the print head 1, and reference numeral 3 represents a position detector connected to the rotating shaft of the motor. These are moved (spaced) along the platen by a feed screw mechanism (not shown), and at the printing position, motor 2 moves the desired type to face the platen, and a hammering motor (not shown) moves the type on the platen. Printing is performed by impacting a print medium through an ink ribbon. The type selection is also the selection of the amount of rotation or displacement of the motor 2, and a signal _S1 instructing this displacement is applied to the speed (displacement) designation circuit 5. Print head 1 has 64 characters arranged in one line as described above, and since the print head rotates in forward and reverse directions, the maximum value of the displacement command is 32 steps, so signal S ₁ is a 6-bit binary value. Consists of signals. The direction of displacement is commanded by a direction control signal S ₂ which _is connected to a direction control circuit 7 which controls the polarity of the output of the amplifier 6.
added to. The 6-bit binary signal _S1 is converted to DA by the speed specifying circuit 5, and as the motor 2 rotates, the print head 1 rotates, and the number of print positions up to the desired print character decreases one by one, the signal S1 is converted. Since ₁ decreases by 1, the output _S3 of the speed designation circuit 5 becomes a step wave that gradually decreases.

FIG. 2 shows the shape etc. of the speed setting signal _S3 outputted by this speed designation circuit 5. (3) in this figure is the signal
S ₃ , and (1) is the position detection signal output by detector 3
Showing S ₄ . Points P ₁ , P ₂ . . . P _o of the signal S ₄ correspond to each character position. (2) is the position pulse _S5 generated at the negative peak of the signal _S4 . As shown in (3) of this figure, the initial value V of the signal _S3 corresponds to the number n of printing positions from the current position of the print head to the desired character, and increases by V/n every time the position signal _S4 strokes one cycle. Decrease.

Since the frequency of the output signal S ₄ of the detector 3 and the signal S ₅ obtained by turning it into a pulse is proportional to the speed of the motor 2, if these are frequency-voltage converted by the speed detector 8, a speed voltage signal S ₆ is obtained. This actual speed signal S ₆ is input to the differential amplifier 6 together with the speed setting signal S ₃ , and the amplifier 6 outputs the difference between the two. After the polarity of the difference signal S ₇ is determined by the direction control circuit, it enters the clipper 9 via the changeover switch 10, and the signal S 7 is truncated if it exceeds a certain value (the value that gives the maximum torque to the motor 2). It then enters motor 2 to rotate it forward or reverse. Initially, the rotational speed 〓θ of the motor 2 and the print head, etc. is zero, and the displacement (speed) command signal
S ₁ and S ₃ (hereinafter also referred to as θ) are maximum values. Therefore, the difference Δθ=θ−K〓θ (K is a coefficient) is a sufficiently large positive value at the beginning of startup, is truncated by the clipper 9 and applied to the motor 2, and the motor 2 accelerates at a constant torque +T. This situation is shown in FIG. In FIG. 4, the drive signal to the motor 2 is given in the form of a current I, and the torque T is shown in the form of the current I. motor 2
As the motor rotates, the displacement (speed) command signal θ decreases and the motor speed 〓θ increases, thus reaching a certain point ta
Finally, the motor speed 〓θ exceeds the command signal θ and the amplifier 6
The polarity of the output is reversed, and a current -I of the opposite polarity flows through the motor 2, applying braking. Braking current-I
is quite large immediately after switching, and due to the clipper 9,
It takes a constant value, but when the speed difference decreases due to deceleration, it enters a proportional range, and the motor speed gradually decreases in accordance with the speed command voltage θ. When the motor 2 rotates sufficiently (and decelerates sufficiently during this period) and enters 1/4 of the final character interval to the desired character, a lock signal _S8 is generated, and the switch 10 is switched to the contact at the top of the drawing to start the motor. 2 is added with the output signal S ₄ of the detector 3, and this signal
Following _S4 , the motor 2 rotates to the desired print position.

According to this print head drive system, when accelerating, +
Although this is rapid acceleration with a constant torque T, during deceleration, especially in the latter half, proportional control is performed according to the speed command that gradually decreases, so the target position can be reached without too much or too little, but the speed command curve is stepwise. Therefore, when the speed command changes, there is a large difference from the actual speed, which causes the motor current to fluctuate violently as shown by the sawtooth waveform in FIG. 4, making the rotation unsmooth. In order to avoid this, in the aforementioned application, a smoother circuit 11 is inserted after the speed designation circuit 5, and the speed command signal θ is smoothed as shown by the dotted line in FIG.
This smoothing is performed by integrating the output _S6 of the speed detection circuit 8 in the smoother circuit 11, and using the integrated value as the speed command signal.
This is done by subtracting it from S ₃ . Since it is necessary to perform the integration for each step of the staircase wave, a pulse generation circuit 12 is provided which receives the position signal _S4 and generates a pulse at each rising edge of the signal, and the output pulse of the circuit 12 is used to perform the integration of the smoother circuit 11. Reset the circuit.

However, in this proposed device, the circuit 11,
12 is relatively complicated and increases costs. On the other hand, in the previously proposed method, as shown in Fig. 2, the speed command signal is changed stepwise only when the sine wave output signal of the position detector 3 has a negative peak, but this is also done when the signal has a positive peak. If you do this, the change frequency is 2
Therefore, the amount of change at one time becomes 1/2, and the staircase wave can be made into multiple small steps and smoothed considerably. Moreover, it is sufficient to simply provide positive and negative peak detection circuits, and the circuit does not become very complicated. As mentioned above, the displacement designation signal _S1 is a 6-bit signal, so it can handle 64 types of binary numbers, and the number of steps is a maximum of 32 centered on the home position, so double this. can be fully covered by a 6-bit binary number.

FIG. 3 shows the waveform of a signal similar to that in FIG. 2 according to the present invention, and (1) is the output signal of the position detector 3, which is exactly the same as FIG. 2 (1). (2) is a position pulse and corresponds to FIG. 2(2), but since the pulse is generated at the positive and negative peaks of the signal _S4 , the frequency is twice that of FIG. 2(2). As a result, the number of changes in the displacement designation signal _S1 is twice that in Figure 2, and the amount of change at each change is 1/2 of that in Figure 2, making it fairly smooth as shown. . Naturally, if the amount of change is small, the change in motor current is also small, and rotation becomes smoother, which in turn shortens the time required for character selection. The signal S ₁ is generated by an arithmetic circuit (not shown), and the position signal S ₄
Also, every time the position pulse S ₅ is input, it decreases by 1 (this corresponds to 0.5 steps in the case of the existing proposal) 6
Outputs a bit binary signal.

As described in detail above, according to the present invention, the speed command signal can be made into multiple stages and small steps by extremely simple means of utilizing the positive and negative peaks of the position signal. If this is done, the difference with the smooth speed voltage signal will not fluctuate as much as in the case of a small number of steps or a high step difference, so the motor drive will be smoother, and the type selection time can be shortened. For example, in the previously proposed method, it takes 25.5 mS to select the farthest printed character 32 characters away from the home position, but in the present invention, this takes 20 mS, which is a reduction of about 20%.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing the circuit configuration of the print head driving section, FIG. 2 is a graph illustrating the previously proposed print head driving method, and FIG.
The figure is a graph showing the relationship between position and speed signals and motor current. In the drawing, 1 is a print head, 2 is a motor, 3 is a position detector, 6 is an amplifier, and 9 is a clipper.

Claims (1)

[Claims] 1. A motor that rotationally drives the print head, a detector that outputs a position signal indicating a change of one cycle per character interval of the print head, and an initial value corresponding to the number of characters to be printed from the current position of the print head. Then, a step-like signal that decreases by a constant value by the output of the detector every time the type head rotates between the type characters, and a speed voltage signal of the print head obtained by frequency-voltage conversion of the position signal are inputted. In the method of driving a print head mechanism of a serial printer comprising an amplifier that outputs a difference signal, a position pulse is generated at each positive and negative peak of the output position signal of the detector, and the number of steps of the step-like signal is doubled. and a method for driving a print head characterized in that the stepped signal is smoothed by reducing the step difference to 1/2.