JPH06440B2 - Pen lifting control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a pen or the like provided in a writing head of an automatic writing apparatus such as an automatic drafting machine or an XY plotter in a vertical direction substantially perpendicular to a writing surface. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pen lifting / lowering control device for driving a pen, and more particularly, to a pen lifting / lowering control device capable of reducing an impact when a pen tip comes into contact with a writing surface.

[Conventional technology]

Generally, automatic drafting machine, automatic drawing machine, XY plotter, X
In an automatic writing apparatus such as a Y recorder, a writing instrument such as a pen is moved up and down in a direction perpendicular to the writing surface to perform so-called pen-up and pen-down operations (pen lifting operation), and the writing instrument is placed on the writing surface. So, for example, X and Y 2
Writing movements are performed by moving relative to each other in the dimensional direction. That is, the pen is moved to the writing start position in the pen-up state, the pen tip is brought into contact with the writing surface by the pen-down operation, and the pen (or the writing position) is written along the desired trajectory to be written with an appropriate writing pressure applied. The desired symbol, figure, etc. is drawn on the writing surface by repeating a series of operations in which the surface side) is relatively moved and the pen tip is floated away from the writing surface by the pen-up operation at the writing end position. Is.

Here, the pen lifting operation is generally performed by a solenoid plunger, and the pen moves down and up in response to energization and interruption of solenoid current. In this case, it is preferable that the pen-down operation is performed when the solenoid is energized, because the pen-up state is maintained when the power is off.

[Problems to be solved by the invention]

By the way, since the tip of the pen collides with the writing surface during the up / down operation of the pen, especially the down operation,
At this time, adverse effects due to impact, such as generation of impact noise, reduction in pen life, and damage to the paper that is the writing surface, especially when writing many numbers, alphabets, kanji, etc., or when the writing speed is high Has a large number of pen ups and downs per unit time, and the occurrence of impact at the tip of the pen during the down operation is a serious problem.

In particular, when the pen of the writing head is a so-called mechanical pencil type writing instrument that uses a pencil lead, the lead may be broken by the impact at the time of pen down, and some shock mitigation measures are required. Not only that, a writing pressure at the time of writing is generally required to be larger than that of an ink type pen, and this writing pressure must be controlled so as to be applied immediately after pen down.

For this reason, the pen is rapidly lowered in response to the input of the pen up / down signal and the landing on the writing surface is performed softly, and after the pen landing on the writing surface, a predetermined appropriate writing pressure is continuously applied. A series of pen lowering operations like this are required,
Such a series of operations needs to be sequentially and sequentially performed using a timer such as a counter, which complicates the configuration and causes a timer to be triggered by noise to cause a pen descending operation. was there.

Further, when the power source for driving the plunger suction changes, the suction force of the plunger also changes, and a smooth pen lowering operation cannot be performed.

The present invention has been made in view of the above circumstances, and it is possible to perform a series of operations from pen lowering to writing pressure application with a relatively simple configuration, and the above series of operations is performed due to noise or the like. A first object of the present invention is to provide a pen lifting / lowering control device that does not accidentally occur.

A second object of the present invention is not only to achieve the first object, but also to suppress the fluctuation of the suction force to be small and to perform a stable pen lowering operation even when the plunger driving power supply fluctuates. It is an object of the present invention to provide such a pen lifting control device.

[Means for solving problems]

In order to solve the above problems, the first application of the present application
According to another aspect of the present invention, there is provided a pen lifting control device which controls a current supplied to a plunger that drives a pen attached to a writing head of an automatic writing device to lift the pen. A counter that starts counting a clock signal in response to an input, and an analog data generator that selectively selects and outputs analog data for setting a supply current to the plunger according to a count output from the counter, The power supply control unit that controls the supply current to the plunger according to the output from the analog data generation unit, and the power supply control unit from the operation prohibited state when the count value of the counter reaches a constant value K _1. and operation switching means for switching the operating state, the clock signal to the counter when the count value of the counter reaches another predetermined value K ₂ It is made and a clock control unit for stopping the counting operation by blocking force.

In addition to the configuration of the first invention, the pen lifting control device according to the second invention of the present application detects the current flowing through the plunger and feeds it back to the input side of the current supply control unit. It is configured by providing current detecting means or current-voltage converting means.

[Work]

According to the configuration of the first aspect of the invention, the operation of the power supply control unit is prohibited and the pen lowering operation is not started until the counter counts the count value K ₁ by the input of the pen up / down signal, and the noise reduction measure is taken. In addition, when the pen descending operation progresses and the counter counts the count value K ₂ , the counting operation is stopped and the analog data from the analog data generator is fixedly held. The applied state can be maintained.

Next, according to the configuration of the second aspect of the invention, in addition to the operation of the configuration of the first aspect of the invention, the detection output of the plunger current from the current detection means is fed back to the power supply control unit, so that the plunger is provided. The current is stabilized and controlled to a value according to the output from the analog data generator, and a stable pen lowering operation can be performed even if the power supply voltage changes.

〔Example〕

Hereinafter, a preferred embodiment of a pen lifting control device according to the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention. A pen plunger 21 of a pen drive unit 20 provided in a writing head unit of an XY plotter, an automatic drawing machine or the like.
A pen lifting control device is shown that controls a current supplied to the pen plunger 21 to lift and lower a pen (including a so-called mechanical pencil type) 23 via the pen drive mechanism 22.

In the first view, and pen lift (up-down) signal P _UD is supplied to the input terminal 1, the pen lift signal P _UD is fed to the gate controller 3 of the clock control unit 2. The clock signal CLK from the clock input terminal 4 is sent to the clock gate 5 of the clock control unit 2. The clock gate 5 controls the clock signal CLK according to the output from the gate controller 3. Then, it is sent to the clock input terminal of the landing counter 6. The pen up / down signal P _UD is also sent to the landing counter 6, and the count output (count output) from this counter 6 is sent to the analog multiplexer 8 of the analog data output unit 7. The analog data output unit 7 is provided with a set voltage generation circuit 9 that generates a plurality of types of set voltages for setting the suction driving force of the pen plunger 21, and the analog multiplexer 8 generates the set voltage. Any one of a plurality of set voltages output from the circuit 9 is sequentially switched and selected and sent to the power supply control unit 10.

The power supply control unit 10 includes, for example, an adder 11, an analog control circuit 12, and an amplifier 13. The analog voltage output from the analog data output unit 7 is the adder 1
1 is sent to the control circuit 12, and the control circuit 12 performs control such that the current flowing through the pen plunger 21 becomes a constant value according to the set voltage, while the amplifier 13
The plunger 21 is drive-controlled via.

Further, as a part of the second invention of the present application, the current flowing through the pen plunger 21 is converted into, for example, a voltage output by the current detection circuit 14 and taken out, and this output is added by the power supply control unit 10. And a so-called feedback control loop is configured.

The power supply control unit 10 is controlled to switch between an operating state (or an active state) and a non-operating state (or an operation prohibited state) according to the output from the operation prohibiting circuit or the operation switching circuit 15. . This can be realized, for example, by prohibiting the operation of, for example, the control circuit 12 in the power supply control unit 10 by the operation prohibition signal S _INH from the operation switching circuit 15.

Here, the landing counter 6 determines a reference time for operation control when the pen descends and lands on the writing surface. When the number of output bits of the landing counter 6 and n + m bits (n, m are natural numbers), LSB is sent to (the least significant bit) from the n-th Q _n operation switching circuit 15 outputs, the Q _n output When it becomes “1” for the first time, the operation prohibition signal S _INH from the operation switching circuit 15 is set to the release state (for example, “0”),
The power supply controller 10 is controlled to switch to an operating state or an active state. Further, each output from the above Q _n of the landing counter 6 to Q _{n + m} of the MSB (most significant bit) is sent to the analog multiplexer 8, and these Q _{n to} Q are output.
The switching selection operation of the analog multiplexer is sequentially performed according to the _{n + m} output. Further, the carry operation CY of the landing counter 6 is sent to the gate controller 3, and when the carry is generated, the clock gate 5 is closed to eliminate the clock input to the landing counter 6, thereby performing the counting operation (counting operation) of the landing counter 6. Are stopped, and at this time, the outputs Q _{n to} Q _{n + m} from the landing counter 6 are held at constant values (all “0”), and the analog multiplexer 8
The set voltage output from is also held at a constant value.

Therefore, even when noise is superimposed on the input system of the pen up / down signal P _UD , the above-mentioned Q in the landing counter 6
_The power supply control unit 10 does not enter the operating state unless it is counted until "1" is output to the _n output, so that it is possible to prevent the pen lowering operation from being started due to the noise. Further, since the output of the analog data output unit 7 is maintained at a constant value at the time when the carry CY is generated from the landing counter 6, it is possible to write while the proper writing pressure is applied. In general, when the landing counter 6 counts a constant value K ₁ , a signal is sent to the operation switching circuit 15 to cancel the operation prohibition state of the power supply control unit 10, and the K ₁ Is also landing counter 6 at the time of counting another large constant value K _2.
The counting operation of 1 may be stopped and the output from the analog data generator 7 may be maintained at a constant value.

Next, the more specific structure and operation of FIG. 1 will be described with reference to FIGS. 2 and 3.

As shown in FIG. 3, a clock signal CLK having a constant period T _c is supplied to the clock input terminal 4 of FIG. In addition, the pen up / down signal P _UD supplied to the input terminal 1
"H" (high level) or "1" corresponds to the pen-up state, and "L" (low level) or "0" corresponds to the pen-down state.

So-called D-type flip-flops are used as the gate controller 3 and the operation switching circuit 15 in FIG. An AND gate is used as the clock gate 5 of the clock control unit 2, and the output from the gate controller 3 is supplied to one input terminal of this clock gate 5 and the clock signal CLK is supplied to the other input terminal. As the landing counter 6, 4-bit Q ₀
A hexadecimal binary counter having .about.Q ₃ output is used, and the clock CK from the clock gate 5 is supplied to the clock input terminal of the counter 6. The pen up / down signal P _UD is supplied to the respective reset terminals R of the gate controller 3, the landing counter 6 and the operation switching circuit 15, and when the pen up state, that is, the pen up / down signal P _UD is “1”, All the circuits 3, 6 and 15 are in the reset state.

Next, of the Q _{0 to} Q ₃ outputs from the landing counter, the lowest Q ₀ output is not used, and the Q ₁ output is sent to the clock input terminal of the operation switching circuit 15, and Q ₁ to Q _{3 are} output.
The Q ₃ output is sent to the switching control input terminal of the analog multiplexer 8. The carry pulse CY from the landing counter 6 is sent to the clock input terminal of the gate controller 3 of the clock controller 2.

The analog multiplexer 8 is the landing counter 6
Depending on the 3-bit Q _{1 to} Q ₃ outputs from the above, any of the eight selected terminals X _{0 to} X ₇ is switched and connected to the output terminal X. The selected terminals X _{0 to} X ₇ of the analog multiplexer 8 are provided with 8 from the set voltage generating circuit 9.
The three set voltages are respectively supplied, and the set voltage V _X according to the selected terminal is sent from the output terminal X to the input terminal of the control circuit 12 of the power supply control unit 10.

The output terminal of the control circuit 12 of the power supply control unit 10 is connected to the base of a PNP type power transistor as the amplifier 13, the emitter of this transistor is connected to the + V _m power source for driving the plunger, and the collector is connected to the pen plunger. One end of the solenoid 21 is connected. The other end of the solenoid of the pen plunger 21 is connected via a current detection circuit 14 or a resistance R _S as a current-voltage conversion means. The resistance R _S and the pen plunger 21 are connected to each other.
The connection point with the solenoid of is connected to the input terminal of the control circuit 12 via a resistor R _t which is a part of the adder 11. By connecting the output terminal X of the analog multiplexer 8 to the connection point between this input terminal and the resistor R _t , the output from the analog multiplexer 8 and the voltage output obtained by detecting the plunger current are added, and the control circuit 12 is obtained. Is supplied to the input terminal of. The control circuit 12 has an operation prohibition input terminal INH, and the output of the operation switching circuit 15 is used as the operation prohibition signal S _{INH and} is _{supplied to} the terminal IN of the control circuit 12.
Sent to H.

In the configuration of FIG. 2 as described above, in the normal pen-up state, as described above, all of the gate controller 3, the landing counter 6, and the operation switching circuit 15 are reset. At this time, the output of the gate controller 3 is "1", and this is sent to the AND gate which is the clock gate 5. Therefore, the clock signal CLK from the input terminal 4 passes through the clock gate 5 and the clock for count input. It becomes CK and is sent to the clock input terminal of the landing counter 6. Since the landing counter 6 is in the reset state as described above, the outputs Q _{0 to} Q ₃ as count outputs are all “0”, and the analog multiplexer 8 sets the selected terminal X ₀ to the output terminal X. Connected. Further, the operation switching circuit 15 is also reset and the output is "1", so that the control circuit 12 of the power supply control unit 10 is in a non-operating state or a state in which the operation is prohibited. At this time, the output from the power supply control unit 10 is at the zero level or in the off state, the pen plunger 21 of the pen drive unit 20 is turned off, and the pen 23 of FIG. 1 is in the up (pen-up) state. Is kept at.

Now, at time t ₀ shown in FIG. 3, the pen up / down signal P
_{When UD} changes from “1” to “0”, the gate controller 3, the landing counter 6, and the operation switching circuit 1
The reset state is released in all of 5, and the landing counter 6 counts the clock CK input after the time t ₀ . Therefore, the Q ₁ output of the landing counter 6 becomes “1” at the time t ₁ when the second clock CK counted immediately after the time t ₀ is input, and this Q ₁ output is supplied to the operation switching circuit 15 as a clock. As a result, the operation inhibition signal S _INH which is the output of the operation switching circuit 15 becomes “0”. Therefore, the operation prohibition state of the control circuit 12 is released, and the power supply control unit 10 becomes the operation state or the activation state. Further, since only the Q ₁ output of the landing counter 6 becomes “1”, the analog multiplexer 8 of the analog data output unit 7 connects the selected terminal X ₁ to the output terminal X.

Since the landing counter 6 sequentially counts the clock CK from the clock controller 2 after the time t ₀ , Q ₁
~ Q ₃ output changes as shown in FIG. 3, and the analog multiplexer 8 is output at every cycle 2T _{c which is} twice the clock cycle T _c.
The selected terminals of are sequentially switched and connected. That is, when the time that has elapsed one by 2Tc from the time _{t 1 t 2, t 3,} ... and, t ₁ ~t fixed terminal X ₁ between the ₂ is the terminal X ₂ between t ₂ ~t ₃ ... are sequentially switched and selected and connected to the output terminal X,
Between the times t _{7 and} t ₈ , the selected terminal X ₇ is selected and the output terminal X
Connected with.

Next, the outputs Q _{0 to} Q ₃ immediately before time t ₈ are all “1”, and when the clock CK is input at time t ₈ , the landing counter 6 causes the carry pulse as shown in FIG. While outputting CY, the outputs of Q _{0 to} Q ₃ are all “0”. By sending this carry pulse CY to the clock input terminal of the gate controller 3, the output of the gate controller 3 becomes "0", and the clock gate 5 is cut off. Therefore, clock C
K is the after the time t ₈ will not be input, output Q ₀ to Q ₃ landing counter 6 is maintained while all "0". At this time, the analog multiplexer 8 selects the selected terminal X ₀ and connects it to the output terminal X.

By the way, as the set voltage generating circuit 9 of the analog data output unit 7 of FIG. 2, eight resistors R are provided to the reference power source of + V _{S.
0 to} R ₇ with one end connected to each other,
The other ends of these resistors R _{0 to} R ₇ are connected to the selected terminals X _{0 to} X ₇ of the analog multiplexer 8, respectively. Therefore, the resistors R _{0 to} R ₇ are sequentially selected according to the count outputs Q _{1 to} Q ₃ from the landing counter 6 and connected to the output terminal X, so that the output terminals X have V _{0 to} V ₇ respectively. The set voltage of is obtained.

In this case, any output voltage _{V X} from the analog data output unit 7, _{R t} is sufficiently larger than the resistance _{R S} of FIG. 2 _(R t »R _S) time, (However, R _X is any one of R _{0 to} R ₇ , and I _P is a current flowing through the plunger 21). In this equation, R _t , V _S , and R _S are constant, and V _X controls the plunger current I _P so that the control circuit 12 is kept constant by the feedback from the current detection circuit 14, Where I _P is the resistance R _x ,
That is, it can be regarded as the function I _P (R _x ) of any one selected from R _{0 to} R ₇ .

In this equation, the conditions for each value are: R _x ≧ 0, R _t >> R _s > 0 V _s > V _x > 0 Further, when the resistance value of the plunger 21 is R _P , V _m / R _P ≧ I _P since ≧ 0 or _{V X / R S ≧ I P} ≧ 0, so that the fourth diagram the graphing case of _{Vm / R P <V X /} R S. In FIG. 4, I ₀
To I ₇ correspond to I _P (R ₀ ) to I _P (R ₇ ) in the above formula, respectively.

Thus, the plunger current I _P with time during pen drop operation changes as Figure 3. That is, at the start of the descent just after the time t ₁ , the large currents I ₁ and I ₂ are made to flow and the pen is rapidly lowered by the large electromagnetic attraction force, and at the times t ₃ and t ₄ , the current is reduced.
I ₃ and I ₄ are made extremely small so as to land softly and softly, the currents I _{5 to} I ₇ are gradually increased after time t ₅ , and finally the count is stopped after time t _8. At times, a constant current I _{0 is made} to flow to apply an appropriate writing pressure to the pen. Therefore, the position H of the pen tip in the vertical direction changes as shown by the solid line in FIG. 3, and the writing pressure applied to the pen tip changes as shown by the broken line in FIG. Then, while the writing pressure is maintained at an appropriate value, the pen and the writing surface are moved relative to each other,
This is the writing.

In the example of FIG. 3, as the writing head pen,
It shows the case of using a pen that uses a pencil lead such as a so-called mechanical pencil type, and the writing pressure when writing is relatively large, but in the case of a pen that uses ink, the writing pressure is smaller. finished may do it by setting the analog multiplexer 8, and the like as it is to hold the current I ₅ at a current I ₃ or time t _5, for example in a time t _3.

Further, in the case of the writing head, when the pen using the pencil lead and the pen using the ink can be combined,
For example, as shown in FIG. 5, set voltage generation circuits 9A and 9B and an analog multiplexer 8 which respectively generate a group of set voltages according to the descent operation of each pen and an appropriate writing pressure.
Two analog data output units 7A and 7B each having A and 8B are provided, and the output from the changeover switch 31 is passed through the inverter 32 to the inhibition input terminal INH of the analog multiplexer 8A, and the output from the changeover switch 31 is directly converted to the analog form. Inhibit input terminal I of multiplexer 8B
It suffices to supply each to NH and send the outputs from these analog multiplexers 8A and 8B to the power supply control unit 10.

Next, when the pen up / down signal P _UD changes from “0” to “1” at time t ₉ , the gate controller 3, the landing counter 6, and the operation switching circuit 15 are reset. At this time, the clock gate 5 of the clock control unit 2 is opened and the clock signal CLK becomes the clock CK for counting.
Is supplied to the landing counter 6, but since the counter 6 is in the reset state, Q _{0 to} Q ₃ are all “0”.
It remains unchanged. Further, the operation switching circuit 15 is reset so that the output operation prohibition signal S _INH becomes “1”,
The control circuit 12 of the power supply control unit 10 is controlled to the operation prohibited state.

According to the pen lifting control apparatus as described above, the operation switching circuit 15 generally releases the operation prohibited state of the power supply control unit 10 until the Q ₁ output of the landing counter 6 becomes “1”. Is the input clock C until the constant value K ₁ is reached.
It is when K is counted, and even if noise such as a single pulse is superimposed on the pen up / down signal P _UD , that is, when P _UD is “1” (pen-up state), it is momentarily “0”. " _PUD returns to" 1 "and the counter 6 is reset before the counter 6 counts the constant value K ₁ even if the value changes to"", so the series of pen lowering operations is not started. Further, when the pen lands on the writing surface and the writing pressure is gradually applied, the time when the carry CY is output from the landing counter 6 (time in FIG. 3).
t ₈₎ at reaching a proper writing pressure, since the gate controller 3 by the carry CY is controlled to close the clock gate 5, the output of the counter 6 is kept constant, setting the voltage output from the analog multiplexer 8 also constant And the proper writing pressure is maintained. Instead of using the carry CY, generally, when the count value of the counter 6 reaches a constant value K ₂ , for example, the clock control unit 2 is controlled so that the clock CK disappears, and the count operation of the counter 6 is stopped. You can do it. Further, the plunger current I _P is detected by a current-voltage conversion element such as a resistor R _S , generally a current detection circuit 14, and the plunger current I _P is detected.
_By feeding back the detection output of _{P to} the control circuit 12 of the power supply control unit 10, the current I _P is controlled to be maintained at a constant value according to the output setting voltage V _X from the analog data output unit 7. Therefore, a stable pen lowering operation can be realized even against disturbance such as power supply fluctuation.

The present invention is not limited to the above-described embodiment, and for example, the output of each bit from the landing counter 6 is supplied to a logic circuit including an AND gate, an OR gate, an inverter, etc. A signal may be sent from this logic circuit to the operation switching circuit 15 when the value K ₁ is reached, and a signal may be sent to the clock control unit 2 when the other constant value K ₂ is reached. In addition, the entire pattern of the set voltage sequentially output from the analog data output unit 7 according to the count output from the landing counter 6 is also
Needless to say, various changes may be made according to the characteristics of the plunger and the drive mechanism, the type of pen used, and the like.

〔The invention's effect〕

As is clear from the above description, the first aspect of the present application
According to the invention, a relatively simple circuit configuration using one counter enables rapid pen movement at the start of pen descent, slow and soft contact of the pen tip when landing on the writing surface, and pen tip movement. Not only is it possible to smoothly and reliably perform a series of operations from the increase of the writing pressure after landing to the holding of the writing pressure, but it is also possible to effectively prevent erroneous operations in the event of noise etc. in the pen-up state. .

Further, according to the second invention of the present application, not only the effect of the first invention, but also the fluctuation of the suction force of the plunger due to the power fluctuation or the like can be suppressed, and the stable pen lowering operation can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of the present invention, FIG. 2 is a block circuit diagram showing a more specific configuration of the embodiment, and FIG. 3 shows an operation of the circuit of FIG. 4 is a timing chart for explaining, FIG. 4 is a graph showing the relationship between the resistance R _X selected in the analog data output section and the plunger current I _P, and FIG. 5 is a block diagram showing the main part of another specific example. is there. 1 ………… Pen up / down signal input terminal 2 ………… Clock control unit 3 ………… Gate controller 5 ………… Clock gate 6 ………… Landing counter 7 ………… Analog data output unit 8 …… ………… Analog multiplexer 9 ………… Set voltage generator 10 ………… Power supply controller 12 ………… Control circuit 14 ………… Current detection circuit 15 ………… Operation switching circuit 21 ………… Pen plunger 23 …… ……pen

Claims (2)

[Claims] 1. A pen lifting control device for controlling a lifting current of a pen attached to a writing head of an automatic writing device by controlling a current supplied to a plunger for driving the pen up and down, wherein a clock is generated according to a pen lifting signal input. A counter for starting signal counting, an analog data generator for selectively selecting and outputting analog data for setting the supply current to the plunger according to the count output from the counter, and the analog data generator. An electric power supply control unit for controlling a supply current to the plunger according to an output from the electric power supply unit, and an operation for switching the electric power supply control unit from an operation prohibited state to an operation state when the count value of the counter reaches a constant value K _1. Switching means and counting when the count value of the counter reaches another constant value K ₂ by cutting off the clock signal input to the counter A pen lifting / lowering control device comprising a clock control unit for stopping operation. 2. A pen lifting control device for controlling a lifting current of a pen mounted on a writing head of an automatic writing device by controlling a current supplied to a plunger for driving the pen up and down, wherein a clock is generated in response to a pen lifting signal input. A counter for starting signal counting, an analog data generator for selectively selecting and outputting analog data for setting the supply current to the plunger according to the count output from the counter, and the analog data generator. A power supply control unit that controls the supply current to the plunger according to the output from the power supply unit; a current detection unit that detects the current flowing in the plunger and feeds it back to the input side of the power supply control unit; operation switching換手for switching the operating state of the power supply control unit from the operation inhibition state when the value reaches a predetermined value K ₁ When the pen lifting control device comprising a clock control unit for stopping the counting operation by blocking the clock signal input to the counter when the count value of the counter reaches another predetermined value K _2.