JPH0813558B2 - Data generator for pulse generator - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus (PWM pulse generation circuit) for generating a pulse having a controlled pulse width. Specifically, in order to generate a pulse having an arbitrary target pulse width from a pulse generator in which the width of the output pulse with respect to the input data varies (or is unknown), a pulse generator for generating a pulse having an arbitrary target pulse width from the source data corresponding to the target pulse width The present invention relates to a data generation device that generates input data.

2. Description of the Related Art Some laser printers used in digital copying machines, laser printers, and the like control the print density by modulating the laser output. In this case, since the laser output is usually controlled by the pulse width, pulse width control (PWM) for converting the print data into pulses having a pulse width corresponding to the print data is required.

In a high-speed laser printer, the processing speed of print data is also high, and the width of the pulse for transferring data is also very short. Here, if information regarding the print density (gradation information) is added to the data of each print dot and the pulse width is controlled according to the print density, it is necessary to use a very high-speed reference clock pulse.
For example, if the print density (gradation) is to be expressed in eight steps, it is necessary to prepare a reference pulse having a width of 1/8 as compared with the case where there is no gradation. However, if the speed of the reference clock pulse is increased, it is necessary to use high-speed peripheral devices accordingly, which significantly increases the cost of the device as a whole. Is difficult to adopt.

Therefore, in order to perform such pulse width control (PWM), a method of generating a PWM pulse by using a delay element instead of using a high-speed reference clock has been considered. This delays a reference pulse (usually a clock pulse) by passing it through several delay elements, and delays it with the delayed pulse (not delayed).
A pulse having a short width (delay time corresponds to this width) is obtained by the difference between the reference pulses.

Problems to be Solved by the Invention A PWM pulse generation circuit (hereinafter, P
To obtain a pulse of arbitrary width from the WM circuit),
The number of delay elements in the PWM circuit, which is the number of delay elements to be used, is input to the PWM circuit.

However, the delay element has slightly different characteristics for each PWM circuit (generally integrated into an IC), and even if the same number of stages of data is input, the pulse width output for each PWM circuit (IC) differs. Even in one PWM circuit, the output pulse width for the same input data (stage number data) varies depending on the temperature of the environment in which it is used and the fluctuation of the power supply voltage.

Conventionally, the variation between individual PWM circuits (IC) was adjusted by taking the relationship between input and output for each IC, but this was time-consuming and labor-intensive. Although this method can eliminate individual differences, it cannot deal with fluctuations in output pulse width due to fluctuations in environmental temperature and power supply voltage.

On the other hand, when the PWM circuit is used in a specific device such as a laser printer, the data (primitive data) for specifying the pulse width output from the PWM circuit cannot be changed according to the temperature of the environment or the power supply voltage. . For example, in a laser printer in which the print density is controlled by the laser output time, data related to print density (hereinafter simply referred to as print data) is input to a PWM circuit to generate a pulse of a predetermined width to be given to a laser generator. Although it is output, the print data cannot be changed according to the individual difference or the characteristic change of the PWM circuit. Therefore, a device for generating the input data of the pulse generation circuit based on the original data (print data in the above example) for generating the pulse of the desired width from the PWM circuit is required.

The relationship between the print data (primary data), the step number data to be input to the PWM circuit, and the pulse width (relative value when the width of the reference pulse is 100%) output from the PWM circuit is shown in the diagram below. It looks like Figure 2. The three straight lines shown in the left half of this graph are the PWM circuit CMIN composed of delay elements with a very short delay time, the PWM circuit CMAX composed of delay elements with a very long delay time, and the middle of them. Comprised of delay elements with a delay time of about
3 shows the relationship between the input stage number data and the output pulse width for three types of PWM circuits, the PWM circuit CMD. For example, to obtain a 50% wide pulse from a PWM circuit CMIN using a delay element with a very short delay time,
It is necessary to input the stage number data having a value larger than that of the intermediate PWM circuit CMD (that is, more delay elements must be used). Also, as mentioned above,
Even with a single PWM circuit, the delay time of the delay element changes due to changes in environmental temperature and power supply voltage, so the relationship between the input data (stage number data) and the output pulse width changes from CMIN to CMAX in some cases.

As described above, even if the step number data obtained by simply converting the print data by the constant relation L is input to the PWM circuit in which the output pulse width fluctuates with respect to the input data, the pulse width obtained by each circuit is obtained. Or, it fluctuates according to the ambient temperature and power supply voltage. For example, even if the print data P50 corresponding to 50% density is input, the pulse width (that is, the actual print density) obtained by that may be t1 which is lower than 50% (in the case of CMIN. ), 100% (that is, black) in some cases (CMAX)). In addition, even if the print data P100 corresponding to 100% density (black) is input, there are cases where only halftone (pulse width t2) is printed (in the case of CMIN).

Another problem of the PWM pulse generation circuit using the delay element is that the pulse generation circuit cannot obtain a pulse having a width equal to or smaller than a predetermined minimum width or larger than a maximum width. Since the pulse generation principle of the PWM circuit using the delay element is as described above, the output pulse of the PWM circuit is originally 0 to 10 of the cycle T of the reference pulse (Fig. 4 (a)).
It should be possible to take any value between 0% (if the number of stages of delay elements is large enough), but in reality, it is limited by the delay characteristics of the output buffer of the PWM circuit, and as shown in FIG. Further, no pulse having a predetermined minimum width tMIN or less is output, and no pulse having a maximum width tMAX or more is output. That is, even if the data of the number of steps corresponding to the width of tMIN or less is input to the PWM circuit, the output remains 0 ((c) in the figure).
Even if the data of the number of stages corresponding to the width of tMAX or more is input, the output remains 1 ((d) in the same figure). Input stage number data and output pulse width for this PWM circuit (reference pulse period T
Is shown in FIG. 3. Therefore, this problem must be taken into consideration when adjusting the PWM output.

The present invention solves these problems, generates an accurate pulse having an arbitrary pulse width, and further takes into account the characteristics of the PWM circuit, and for a PWM circuit to obtain a pulse output that correctly corresponds to atomic data. An object is to provide an input data generation (or data conversion) device.

Means for Solving the Problems In order to achieve the above object, the present invention corresponds to a target pulse width in order to generate an output pulse So having a target pulse width from a pulse generator 10 as shown in FIG. In the device for generating the input data for the pulse generator from the source data Do, the source data Do is generated based on a predetermined conversion relation.
A conversion means 12 for converting the input data Di into 10 and a conversion relation changing means 14 for changing the predetermined conversion relation.
Pulse detection means 18 for detecting whether or not a pulse is generated at the output of the pulse generator 10, and the source data Do and the input data Di at the time when the pulse starts to be generated at the output of the pulse generator 10. And a conversion relation holding means 16 for holding the conversion relation of.

Operation In the above-mentioned configuration, the pulse detecting means 18 and the conversion relation changing means 14 detect the conversion relation at the time when the pulse is started to be output from the pulse generator 10. That is, if the pulse is not output yet, the conversion relation in the conversion means 12 is changed to output the input data Di in the direction in which the pulse is output.
Is changed, and if the pulse has already been output, the input data Di is changed in such a direction that the pulse is no longer output.
Here, the state in which no pulse is output means not only the state of FIG. 4 (c) but also the state of FIG. 4 (d).
The conversion relationship holding means 16 holds the conversion relationship between the source data Do and the input data Di at the time when the pulse starts to be output.

After the calibration by the detection of the pulse generation time is completed in this way, when the original data Do corresponding to the desired pulse width is put into the conversion means 12, the conversion means 12 has the conversion relation holding means 16
Input data Di is created on the basis of the above-mentioned relationship held in the pulse generator 10 and input to the pulse generator 10. This ensures that no pulse is generated from the pulse generator 10 for any source data Do.
You will be able to generate So.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.
FIG. 5 is a block diagram of a pulse width control (PWM) pulse generation circuit for adjusting the laser output of the laser printer of the digital copying machine. In this embodiment, the pulse generation circuit 50 includes an inverter INV, four delay elements D1, D2,
It is composed of D3, D4, a selector 32 for selecting whether or not to include these delay elements in the circuit, and an AND circuit AND. The pulse generating circuit 50 generates a pulse Sb having an arbitrary width (however, within the period of the reference pulse Sa) based on the reference pulse Sa, and its principle is as follows.

The reference pulse Sa is divided into two routes in the pulse generation circuit 50, is inverted / delayed in one route (upper side in FIG. 5), and is input to the AND circuit as it is in the other route. Therefore, the AND circuit outputs a pulse Sb having a width corresponding to the time delayed by the delay element.

Here, by inputting the stage number data Di to the selector 32, the delay elements (D1, D2,
One or a combination of two or more of D3 and D4) is selected and the delay time can be adjusted, so that a pulse having a width corresponding to the input data Di is eventually output from the pulse generation circuit 50. The pulse generation circuit 50 plays a role of generating a pulse having a width proportional to the print density from data for adjusting the print density used in the laser printer (hereinafter, simply referred to as print data). is there. Therefore, a multiplier 36 for multiplying the correction coefficient Da for converting the print data into the step number data and an adder 38 for adding the offset value Db are provided.

However, there are individual differences in the delay element units (the ones in which D1, D2, D3, and D4 are formed on one substrate) that make up the pulse generation circuit 50, and even with one delay element unit, Since the delay time changes due to the influence of the environmental temperature, the power supply voltage, etc., the relationship between the input stage number data Di and the output pulse width changes (FIG. 2). When the print data has a value close to 0 or a value close to 100%, due to the characteristics of the PWM circuit as shown in Fig. 3, the print of the density corresponding to the print data is not always performed. There are cases where it does not exist.

Therefore, in the present embodiment, by using the microcomputer 30, the correction coefficient data Da and the offset data Db when converting the print data into the step number data Di are sequentially corrected as follows, and the print data and the PWM output Sb ( That is, the adjustment is performed so as to approach an ideal state in which the relationship with the print density is always correct.

First, in this embodiment, the pulse detection circuit 40 for detecting whether a pulse is output from the AND circuit is provided. Here, the pulse detection circuit 40 detects the time when a pulse starts to be detected as shown in FIG. 4 (b) from the state shown in FIG. 4 (c) or (d).

FIG. 6 shows a specific configuration example of the pulse detection circuit. Here, the pulse detection circuit (a) has three D flip-flops.
It consists of DFF and one AND circuit.

Next, in the PWM pulse generation circuit with the above configuration, the PWM circuit starts to generate pulses exactly when the print data is 0 (white) and 100% (black) (the pulse disappears at 100%). The operation of the microcomputer 30 when calibrating the relationship between the print data and the width of the output pulse will be described.

In this case, the microcomputer 30 performs the calibration process as shown in FIG. 7 using the output of the pulse detection circuit 40, and the correction coefficient data D for obtaining the ideal PWM output Sb for the print data.
Create a and offset data Db. First, in step # 10, the value "0" is given to the first location of the register 34 as the test data IP. In addition, this place of the register 34 is
In the normal state, the print data P is being input. In the next step # 12, the offset data Db is incremented by 1 from the current value. The correction coefficient data Da remains the current value. This allows the test data to be
IP (= 0) is multiplied by the correction coefficient data Da, and the adder 38 adds the multiplication result Dc (= 0) and the offset data Db to obtain input data (stage number data) Di, which is given to the selector 32. In step # 14, it is determined based on the detection result from the pulse detection circuit 40 whether a pulse is detected in the PWM output Sb corresponding to the input data Di thus created. If no pulse is detected here, the process returns to step # 12 and the value of the offset data Db is further increased by 1. In this way, the offset data Db is increased, and when the pulse is first detected from the pulse generation circuit 50, the process proceeds to step # 16, and the value of the offset data Db at that time is set in the register 34.

Next, in step # 18, the test data IP is set to the value P100 corresponding to 100% density (black), and the correction coefficient data Da is changed (increase or decrease) by 1 by the loop of step # 20 and step # 22. At the same time, the pulse generation circuit 50 detects the time when the pulse starts to be detected. More specifically, here, the pulse detection circuit 40 detects the point at which the pulse of tMAX in FIG. 4B starts to be output from the state of FIG. 4D. If no pulse is detected, step # At 20, the correction coefficient data Da is decreased by 1, and if a pulse is detected, Da is increased by 1, and step #
At 22, the time when the pulse starts to appear or the time when the pulse starts to disappear is detected. When this point is detected, the process proceeds to step # 24, and the correction coefficient data Da at that time is registered.
Set it to 34 and finish the calibration process.

The above calibration process will be described as follows with reference to FIG. Initially, the relationship between the input (stage number) data of the PWM circuit and the pulse width is represented by the line Co on the left side of the graph in the figure, and the line Lo is also used to convert the print data to the stage number data accordingly. It is assumed that the data was correctly converted into the pulse width. That is, print data corresponding to 50% density
When P50 was input, a pulse of exactly 50% width was output from the PWM circuit due to the lines Lo and Co. However, the characteristics of the delay element of the PWM circuit change (delay time shortens) due to changes in the ambient temperature or changes in the power supply voltage,
It is assumed that the relationship between the output pulse width and the input stage number data changes as shown by line C1. At this time, print data of 50% density
If P50 was converted to stage number data by line Lo, the output pulse width would be t1, a value smaller than 50%,
The density according to the print data cannot be obtained (print density becomes lighter). Also, print data that is very small but not 0
Even if Po is given, the PWM circuit does not output a pulse for such a small number of steps data. In this case, even if non-zero print (density) data is input, no print is performed (PWM output = 0%), which is not preferable for a printer.

Therefore, in the processing up to step # 16 of the above calibration processing, the test data IP is first set to 0, the offset data Db is increased, and the point from which the pulse generation circuit 50 starts to output a pulse is detected. This corresponds to translating the data conversion line Lo to the line L1 (), which causes 0
A pulse is always output for non-print data, and the output pulse width can be calibrated for print data having a value close to 0.

However, due to the variation of the delay characteristic of the delay element, the pulse of the correct width is not yet output for the general print data. Therefore, in the processing of steps # 18 to # 24, the print data P100 of 100% density is set as the second step. Correct correction line L2 is changed by changing correction coefficient data Da (changing the slope of data conversion line L1) so that the point where the pulse just starts to correspond to
().

By the above two-step calibration process at the 0% density (white) point and 100% density (black) point using the pulse detection circuit 40, the line L
As can be seen from 2, the correct print density can be obtained over almost the entire print data. Therefore, the calibrated correction coefficient data Da and offset data are registered in the Db register 34.
, And thereafter, by giving the actual print data P to the place where the test data IP of the register 34 was placed, the print data is converted into a pulse having a width corresponding to the density value represented by it. Output to laser printer. In other words, even if the print data of a very small value is not printed, it prevents the print data of a value close to 100% from becoming an intermediate density or being crushed in black, and it corresponds to that value almost in the entire print data. Printing with the specified density is performed.

It should be noted that the offset of the output pulse width with respect to the print data having a very small value is ignored, that is, the calibration at the 0% density point is not performed, and the offset data Db is set to 0 to 100.
It is also possible to calibrate only the% density points (only the correction coefficient data Da). Even in this case, as indicated by the thick dotted line L3 in FIG. 8, the output pulse width is calibrated so that it is almost in proportion to the print data as a whole, so it is calibrated against individual differences and environmental temperature / power supply voltage fluctuations. Can be used sufficiently.

Although the embodiment of FIG. 5 described above is software-controlled by the microcomputer 30, an example of performing similar PWM control in hardware by a counter or the like will be described next with reference to FIG. The basic configuration of this embodiment is similar to that of the circuit of FIG. 5, and includes a pulse generation circuit 50, a pulse detection circuit 40, and a multiplier.
36 and the adder 38 are the same as in FIG. In the second embodiment, an up / down (U / D) counter 58 is used instead of the microcomputer 30.
Correction coefficient data Da based on the pulse detection results.
The optimum correction coefficient data Da and the offset data Db are determined by increasing or decreasing the value of the offset data Db or by one. With the PWM circuit of this configuration, the 0% density (white) point is used by using the pulse detection circuit 40 as described above.
A method of calibrating the correction coefficient data Da and the offset data Db at the 100% density (black) point will be described below.

In this PWM circuit, from the mode switching signal generation circuit 64, the switching signal T1 is input to the data selector 52, the switching signal T2 is input to the correction coefficient data Da register 56, and the offset data Db register 62 is input.
It is possible to perform calibration in various modes by applying the switching signal T3 to and the switching signal T4 to the detection mode switch 60, respectively. Using the pulse detection circuit 40, 0% concentration point and 10
In the mode where the same calibration as in the first embodiment is performed at the 0% density point, in the first stage (FIG. 8), 1) the data selector 52 is switched to the test data IP side by the mode switching signal generation circuit 64. Switching signal T1 for 2), a switching signal T2 for not outputting data from the correction coefficient data register 56 to the multiplier 36, 3) a switching signal T3 for outputting data from the offset data register 62 to the adder 38, 3 switching signals T1 to T3 are output.

When the pulse detection offset calibration mode is entered by giving such a switching signal, the test data IP is first given as "0" to the multiplier 36 via the register 54. In the multiplier 36, the test data IP is multiplied by the correction coefficient data Da, but since the IP is 0, the multiplication result is 0.
The data Dc of the multiplication result is added to the offset data Db by the adder 38, and is input to the pulse generation circuit 50 as the stage number data Di (= Db). The pulse detection circuit 40 checks whether or not a pulse is generated in the output from the pulse generation circuit 50 at this time. The output value of the U / D counter 58 increases when the pulse has not yet occurred (state of FIG. 4 (c)), and when the pulse has already occurred, the counter 58
The value of decreases. The counter value thus incremented or decremented is sent only from the register 62 to the adder 38 (multiplier
It is not sent to 36), but as shown in FIG. 8, it acts so as to move the current data conversion line Lo in parallel to bring it closer to the conversion line L1. In this way, the offset data Db is increased, and the value Db at the time when the pulse just starts to appear is set in the register 62.
Set to.

At the next stage, the mode switching signal generation circuit 64 outputs the data 2) ′ from the correction coefficient data register 56 to the multiplier 36, the switching signal T2 and 3) ′ the offset data register 62 to the adder 38. A switching signal T3 for not outputting the signal is sent to the registers 56 and 62. T1 remains the same.

When the pulse detection correction coefficient data calibration mode is entered by applying such a switching signal, this time the test data
IP is set to P100 and given to the multiplier 36 via the register 54. This data is multiplied by the correction coefficient data Da in the multiplier 36, added by the adder 38 with the offset data Db set in the above processing, and input to the pulse generation circuit 50 as the stage number data Di. Then, the pulse detection circuit 40 checks whether or not a pulse is generated in the output from the pulse generation circuit 50. The output value of the U / D counter 58 decreases when the pulse has not yet occurred (state of FIG. 4D), and increases when the pulse has already occurred. The value of the counter thus incremented or decremented is stored in register 56.
Is sent to the multiplier 36 only (not to the adder 38), and acts to change the slope of the line L1 to bring it closer to the correct conversion line L2, as shown in FIG. In this way, the correction coefficient data Da is increased / decreased, and the value Da at the time when the pulse just starts to be output is set in the register 56.

After calibrating the offset data Db and the correction coefficient data Da in this way, the data selector 52 is switched and the normal print data P is put in the data register 54, whereby the print data P is corrected by the multiplier 36. It is multiplied by the data Da and added by the offset data Db calibrated by the adder 38 to create the correct stage number data Di. Therefore, the width of the output pulse Sb becomes a value proportional to the print data P over almost the entire print density (FIG. 8), and the print density according to the data is obtained.

As described above, according to the present invention, the relationship between the input data and the output pulse width changes (or is unknown).
It is possible to always generate a pulse with a desired width even by using a pulse generator. Therefore, when a pulse generator with individual differences is incorporated in an applied device, or when the pulse width of a PWM pulse generator incorporated in the device is not stable due to factors such as ambient temperature and power supply voltage, the present invention It is possible to use the data generation device according to the above. As a result, it is not necessary to change the original data (print data, etc.), and it is possible to perform PWM control that can always obtain a stable pulse width output for the original data. Further, even if the pulse generator has a characteristic that it cannot generate a pulse having a width equal to or smaller than a predetermined minimum width or larger than a maximum value, such a characteristic is compensated for,
The most desirable relationship between the source data and the output pulse width can be set.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to the claims of the present invention. FIG. 2 is a graph showing a relationship between print data and step number data (right side) and a relationship between input step number data and output pulse width (left side) of a pulse generator using a delay element. FIG. 3 is a graph showing the difference between the input stage number data and the output pulse width of the pulse generator using the delay element, particularly when the input stage number data is very small and very large. FIGS. 4 (a) to 4 (d) are explanatory views showing the state of the pulse generated from the pulse generator using the delay element. FIG. 5 is a block diagram showing the configuration of the PWM pulse generation circuit according to the first embodiment of the present invention. FIG. 6 is a circuit diagram showing a specific configuration example of the pulse detection circuit. FIG. 7 is a flowchart of the processing performed by the microcomputer of the first embodiment. FIG. 8 is an explanatory diagram for explaining the calibration process performed in the first and second embodiments. FIG. 9 is a block diagram showing the configuration of the PWM pulse generation circuit according to the second embodiment of the present invention.

Claims (1)

[Claims] 1. An apparatus for generating input data for a pulse generator from source data corresponding to a target pulse width in order to generate an output pulse having a target pulse width from a pulse generator, wherein the source data has a predetermined conversion relation. A conversion means for converting the input data of the pulse generator based on the above, a conversion relation changing means for changing the predetermined conversion relation, and a pulse detection means for detecting whether or not a pulse is generated at the output of the pulse generator. A pulse generator data generation device comprising: a conversion relationship holding unit that holds a conversion relationship between the source data and the input data at the time when a pulse starts to be generated at the output of the pulse generator.