Method of controlling beam scanning timing and beam energy and light beam scanning apparatus using the same

Disclosed herein is a method of controlling beam scanning timing and beam energy and a light beam scanning apparatus using the method. The light beam scanning apparatus includes a beam generation and processing means, a calculation and control means, a diffraction and scanning means and a scanning and processing means. The beam generation and processing means generates a beam and converts the beam into collimated light. The calculation and control means calculates scanning periods and beam energy, controls the operation periods and diffraction amounts of pixels of a light modulator. The diffraction and scanning means diffracts and modulates the beam and scans a plurality of diffracted beams.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to a method of controlling beam scanning timing and beam energy and a light beam scanning apparatus using the method and, more particularly, to a method of automatically controlling refracted beam scanning timing and beam energy and a light beam scanning apparatus using the method.

2. Description of the Related Art

In general, optical signal processing has the advantages of high-speed processing, parallel processing and high-capacity processing capabilities, unlike conventional digital information processing that cannot process a large amount of data in real time. Research on the design and manufacture of a binary phase only filter, an optical logic gate, an optical amplifier, an image processing technique, an optical element and a light modulator is carried out using a spatial light modulation theory. The light modulator is applied to the fields of optical memory, an optical display, a printer, an optical interconnection and a hologram, and the research and development of a light beam scanning apparatus using the light modulator is being conducted.

Such a light beam scanning apparatus functions to produce an image by scanning a light beam and spotting the light beam on a light-sensitive medium in an image production apparatus, such as a laser printer, a Light Emitting Diode (LED) printer, an electrophotographic copier or a word processor.

Recently, with the development of a projection television, such a light beam scanning apparatus is being used as a means for scanning a beam onto an image display.

A light modulator is not necessarily applied to such a light beam scanning apparatus. For example, a conventional light beam scanning apparatus shown inFIG. 1is not provided with a light modulator. The construction of the conventional light beam scanning apparatus is described in detail below.

Referring toFIG. 1, the conventional light beam scanning apparatus includes a light source110, a control unit120, a lens130, a rotating mirror140, an F-theta lens150, a focusing lens160, and a horizontal synchronization signal sensor170.

The light source110may be implemented with a laser or laser diode that generates a laser beam. The light source110generates a laser beam while being turned on/off according to the operation control of the control unit120.

The control unit120receives a timing value for beam scanning from the horizontal synchronization signal sensor170, and controls the on/off operation of the light source110and the operation of the rotating mirror140.

The lens130focuses a laser beam, generated by the light beam110, toward the reflecting surface of the rotating mirror.

The rotating mirror140is turned on/off according to the operation control of the control unit120, and is rotated at a preset uniform rotational velocity during operation. The rotating mirror140is implemented with a polygonal rotating mirror, so that it reflects an incident beam using the reflecting surface thereof while rotating. In this case, a beam reflected by a reflecting surface of the rotating mirror140is scanned onto a scanning object180while forming a beam spot arrangement with spots arranged at regular intervals. The beam spot arrangement is formed in a line along the length of the scanning object180. Although a beam reflected by the next reflecting surface also forms a beam spot arrangement along the length of the scanning object180, this beam spot arrangement is located below the previous beam spot arrangement while being spaced apart from the previous beam spot arrangement by a specific interval. As a result, the beam spot arrangements formed by the beams reflected by the reflecting surfaces of the rotating mirror140are formed along the length and circumference of the scanning object180.

The rotating mirror140is equipped with a motor (not shown). The rotating mirror140reflects a beam, emitted through the lens130, toward the scanning object180while being rotated by the motor. Such a rotating mirror may be implemented with a polygon mirror or Galvano mirror.

When the polygon mirror is employed as the rotating mirror140, the rotating mirror140becomes characterized by moving a beam emitted through the lens130at uniform velocity.

When the Galvano mirror is employed as the rotating mirror140the rotating mirror140becomes characterized by moving a beam, emitted through the lens130, at nonuniform velocity.

The F-theta lens150scans a beam, scanned by the rotating mirror140, onto the scanning object180while keeping scanning velocity uniform by keeping the scanning distance between the current reflecting surface of the rotating mirror140and the scanning surface of the scanning object constant, thus adjusting the interval between the spots of a beam spot arrangement to a constant distance. Depending on whether the F-theta lens150is present, the interval between the spots of a beam spot arrangement, formed on the scanning object180, varies. The examples are illustrated inFIGS. 2aand2b.

FIG. 2ashows a beam spot arrangement formed on the scanning object180in the case where the conventional light beam scanning apparatus is equipped with the F-theta lens150. In this case, the beam spots are regularly arranged.

FIG. 2bshows a beam spot arrangement formed on the scanning object180in the case where the conventional light beam scanning apparatus is not equipped with the F-theta lens150. In this case, the beam spots are irregularly arranged.

The focusing lens160focuses a beam scanned through the F-theta lens150, and scans the beam on the scanning object180.

The horizontal synchronization signal sensor170receives a reference beam spot indicating the start of printing or image display from the rotating mirror140, sets timing for beam scanning time, which starts from the time when the reference beam spot is received, with respect to a current reflecting surface, and outputs a timing value to the control unit120. At this time, the horizontal synchronization signal sensor170sets the timing for beam scanning time that extends to the time of receiving a reference beam spot reflected by the reflecting surface next to the current reflecting surface.

Though the conventional light beam scanning apparatus employs an F-theta lens to keep the interval between the beam spots of a beam spot arrangement constant on a scanning object, the F-theta lens is disadvantageous in that a long developing period is required and high manufacturing cost is incurred due to difficulty with manufacture and design.

Furthermore, a conventional light beam apparatus equipped with a light modulator keeps the interval between the beam spots of a beam spot arrangement constant using the F-theta lens. In this case, the same disadvantages are incurred because the F-theta is employed.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a method of controlling beam scanning timing and a light beam scanning apparatus using the method, which are capable of keeping the interval between the beam spots of a beam spot arrangement uniform by automatically adjusting the scanning timing of a reflected beam that will be scanned onto a scanning object.

Another object of the present invention is to provide a light beam scanning apparatus, which is capable of keeping the interval between the beam spots of a beam spot arrangement uniform by automatically adjusting the scanning timing of a reflected beam that will be scanned onto a scanning object, thus reducing manufacturing cost.

Another object of the present invention is to provide a method of controlling beam energy and a light beam scanning apparatus using the method, which is capable of making beam energy distribution uniform on the scanning surface of a scanning object by automatically adjusting the individual pixels of a light modulator.

In order to accomplish the above object, the present invention provides a light beam scanning apparatus, including a beam generation and processing means for generating a beam, converting the beam into collimated light; a calculation and control means for calculating scanning periods and beam energy for intervals between beam spots arranged on a scanning object along a scanning line, controlling the operation periods and diffraction amounts of pixels of a light modulator, which diffracts and modulates the beam emitted from the beam generation and processing means, according to the calculated scanning periods and beam energy; a diffraction and focusing means for diffracting and modulating the collimated light, which is emitted by the beam generation and processing means, according to the control of the calculation and control means on the operation periods and diffraction amounts of the pixels of the light modulator, and focusing a plurality of diffracted beams; and a scanning and processing means for scanning the plurality of beams, which are obtained by the diffraction and focusing means, while moving the plurality of diffracted beams at uniform velocity.

In addition, the present invention provides a method of controlling scanning periods in a light beam scanning apparatus, including the first step of calculating a scanning time difference Δt between neighboring beam spots based on a program using an initial rotation angle value θ of a rotating mirror, a linear beam velocity v on a scanning surface of a scanning object and an interval Δx between beam spots arranged on the scanning surface along an x axis when the initial rotation angle value θ and the linear beam velocity v are calculated and the interval Δx is set; the second step of calculating a rotation angle value Δθ of the rotating mirror for the calculated scanning time difference Δt using a uniform angular velocity Ω of the rotating mirror when the scanning time difference Δt is calculated; the third step of updating the initial rotation angle value θ into the calculated rotation angle valve Δθ and calculating a new scanning time difference Δt between beam spots using the rotation angle value Δθ; and the fourth step of calculating and storing sampling time intervals between beam spots arranged on the scanning surface by repeating the first to third steps.

In addition, the present invention provides a method of controlling beam energy in a light beam scanning apparatus, including the first step of calculating sampling time intervals Δt between neighboring beam spots and determining a shortest scanning time difference Δtmin between beam spots using calculated sampling time intervals; the second step of calculating time weights R for intervals of a beam spot arrangement by dividing the shortest scanning time difference Δtmin by the calculated sampling time intervals Δt; and the third step of determining diffraction amounts R of beams by multiplying the calculated time weights R by maximum beam energy Rmax.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3is a configuration diagram of a light beam scanning apparatus using beam scanning timing and beam energy in accordance with an embodiment of the present invention.

Referring toFIG. 3, the light beam scanning apparatus includes a light source210for generating a laser beam, at least one collimator lens220for converting the laser beam, emitted by the light source210, into collimated light, a light modulator230for diffracting and modulating the collimated light obtained through the collimator lens210, and outputting N (N is a natural number) beams, a rotating mirror240for scanning the diffracted beams, outputted by the light modulator230, by moving the diffracted beams, at least one lens250for focusing the diffracted beams output by the light modulator230, a focusing lens260for focusing the diffracted beams, reflected by the rotating mirror240, onto the scanning object201, a scanning period and beam energy determination unit270for determining the scanning period and beam energy of beam spots, which will be arranged on the scanning line of the scanning object201, by calculating the scanning period and the beam energy, and a control unit280for controlling the operation period and diffraction amount of the pixels of the light modulator230according to the scanning period and beam energy of beam spots determined by the scanning period and beam energy determination unit270.

The present invention further includes a horizontal synchronization signal sensor290for receiving a reference beam spot scanned onto the scanning object201through the focusing lens260, setting the timing of beam scanning time starting from the time of receiving the reference beam spot, and outputting a timing value. When the light beam scanning apparatus according to the present invention is applied to a printer, the light beam scanning apparatus is equipped with the horizontal synchronization signal sensor290.

The light source210may be implemented with a laser or Laser Diode (LD) that generates laser beams. The laser diode, which constitutes the light source210, has relatively low output because it scans a plurality of beams at the same time and, thus, can provide a long scanning time, which is required for exposure, to a single pixel.

The collimated lens220is located between the light source210and the light modulator230. When two or more collimated lenses220are employed, the collimated lenses220are arranged at regular intervals.

The light modulator230can simultaneously control a minimum of two pixels. The light modulator230can simultaneously control several hundred to several thousand pixels.

Since the light modulator230can control pixels in an analog fashion, it can perform Gray control when it is applied to a printer and display products. The light modulator230can control the size of a corresponding beam spot and the interval between beam spots by controlling an optical lens and a light projection distance.

The rotating mirror240is equipped with a motor (not shown), and can scan diffracted beams while being rotated by the motor. The rotating mirror240may be implemented with a polygon mirror or Galvano mirror.

When the polygon mirror is used as the rotating mirror240, the rotating mirror240becomes characterized by moving diffracted beams, output from the light modulator, at uniform linear velocity. At this time, the focusing lens260deflects the diffracted beams, reflected by the polygon mirror in a main scanning direction, by focusing the diffracted beams.

When the Galvano mirror is employed as the rotating mirror240, the rotating mirror240becomes characterized by moving the diffracted beams, output from the light modulator230, at nonuniform linear velocity. At this time, the focusing lens260deflects the diffracted beams, reflected by the Galvano mirror, by focusing the diffracted beams.

The lens250is located between the light modulator230and the rotating mirror240. When two or more lenses250are arranged, the lenses250are arranged at regular intervals.

The rotating mirror240is turned on/off according to the operation control of the control unit290, and is rotated at preset uniform rotational velocity during operation. The rotating mirror240is formed in a polygonal shape, and reflects incident light using the reflecting surfaces thereof while being rotated. In this case, the beams reflected by a reflecting surface of the rotating mirror240are scanned onto the scanning object201while forming a beam spot arrangement with spots arranged at regular intervals. The beam spot arrangement is formed in a line along the length of the scanning object201. Although a beam reflected by the next reflecting surface also forms a beam spot arrangement along the length of the scanning object201, this beam spot arrangement is located below the previous beam spot arrangement while being spaced apart from the previous beam spot arrangement by a specific interval. As a result, the beam spot arrangements formed by the beams reflected by the reflecting surfaces of the rotating mirror240are formed along the length and circumference of the scanning object201.

The horizontal synchronization signal sensor290receives a reference beam spot indicating the start of printing or image display from the rotating mirror240, sets timing for beam scanning time, which starts from the time when the reference beam spot is received, with respect to a current reflecting surface, and outputs a timing value to the control unit280. At this time, the horizontal synchronization signal sensor290sets the timing for the beam scanning time that extends to the time of receiving a reference beam spot reflected by a reflecting surface next to the current reflecting surface of the rotating mirror240, and outputs the timing value to the control unit280.

When the timing value for a current horizontal scanning line calculated by the horizontal synchronization signal sensor290is input to the control unit280, the control unit280causes beam spots to be scanned onto the current horizontal scanning line of the scanning object201by operating the light modulator230for the time value.

If a reference beam spot for a horizontal scanning line immediately below the current horizontal scanning line is not received by the horizontal synchronization signal sensor270after the beam scanning time for the current horizontal scanning line, which corresponds to the timing value calculated by the horizontal synchronization signal sensor270, has elapsed, the horizontal synchronization signal sensor270does not set timing for beam scanning time with respect to a new scanning line. Accordingly, a timing value for new horizontal beam scanning is not input to the control unit290. As a result, the control unit290stops the operation of the light modulator230.

FIG. 4is a diagram illustrating the calculation process of the beam scanning period and beam energy determination unit provided in the light beam scanning apparatus according to the present invention. The process of calculating a beam scanning period and beam energy is described in detail with reference toFIG. 4.

The variables of the following equation are defined as described below.

Referring toFIG. 4, “x” is a horizontal axis that horizontally passes through the rotation axis CT1of the rotating mirror240, “y” is a vertical axis that vertically passes through the rotation axis CT1of the rotating mirror240, “r” is a distance that extends from the rotation axis CT1of the rotating mirror240to the center of a reflecting surface RF, “θ” is an angle that a straight line forms with the x axis in the case where the rotation axis of the rotating mirror CT1is connected to the center CT2of the reflecting surface RF by the straight line, “d” is the rectilinear distance between the x axis and the scanning surface of the scanning object201, “Ω” is the uniform angular velocity of the rotating mirror240, “n” is a coordinate point on the y axis that is a coordinate value existing on the same horizontal line as the light emitting point of the light modulator230, “φ” is an angle that a horizontal line horizontally passing through the reflecting point RP of the rotating mirror240forms with a beam incident from the light modulator230in the case where the beam incident from the light modulator230is reflected at the reflecting point RP, and “m” is a coordinate point on the x axis that is a coordinate value existing on the same vertical line as the light emitting point of the light modulator230.

The plane equation of beam scanning on the current reflecting surface RF of the rotating mirror240is expressed as the following Equations 1 and 2.
F1(x, y, r, θ)=0  (1)
xcos θ+ysin θ=r(2)

The rectilinear equation of a beam incident from the light modulator230to the reflecting point RP of the rotating mirror240is expressed as the following Equations 3 and 4.
F2(x, y, n, m, φ)=0  (3)
y=tan φx+n−mtan φ  (4)

The rectilinear equation of a beam reflected from the reflecting point RP of the current reflecting surface RF of the rotating mirror240is expressed as the following Equations 5 and 6.
F3(x, y, n, r, φ)=0  (5)
x=(r−nsin θ)/cos θ+(y−n)cot 2θ  (6)

When a beam reflected from the current reflecting surface RF of the rotating mirror240is scanned onto the scanning object201, the trace of a beam on a scanning surface is expressed as the following Equations 7 and 8.
x=F4(n, m, r, d, θ, φ)  (7)
x=(r−nsin θ)/cos θ+(d−n)cot 2θ  (8)

Since a beam, which the rotating mirror240reflects using the reflecting surface thereof while being rotated, is scanned onto the scanning object201, the beam scanned onto a scanning surface in an x direction has linear velocity. The linear velocity v of the beam on the scanning surface is expressed as the following Equation 9.
v=dF4/dt=dF4/dθ*dθ/dt=dF4/dθ*Ω(9)
where dθ/dt is the uniform angular velocity Ω of the rotating mirror.

Since the linear velocity v of a beam scanned onto the scanning surface of the scanning object201varies as represented by the above Equations, the interval between the beam spots is not uniform. In the conventional beam scanning apparatus, the nonuniformity of the interval occurring between the beam spots due to the variation of the linear velocity of beams is overcome using an F-theta lens.

However, the F-theta requires a long manufacturing period and expensive manufacturing cost, so that the present invention does not employ the F-theta lens, but makes the interval between beam spots uniform using the following scheme.

FIG. 5is a flowchart showing the process of calculating beam scanning timing in a light beam scanning apparatus in accordance with the present invention.

A manufacturer sets an initial θ vale at step S501. Thereafter, the manufacturer calculates the linear velocity v of a beam on the scanning surface by substituting the initial θ value for the corresponding variable of Equation 9 at step S502.

When the initial θ value and the linear velocity v of the beam on the scanning surface are obtained as described above and the interval Δx between beam spots arranged on the scanning surface along the x axis is determined by the manufacturer, the scanning period and beam energy determination unit270calculates the scanning time difference Δt between neighboring beam spots by executing Equations 10 and 11 according to a predetermined program at step S503. In this case, Δx is the x axis coordinate distance between neighboring beam spots, and Δt is a sampling time interval that allows a beam scanned onto the scanning surface to have uniform linear velocity.
Δx=dx/dθ*dθ/dt*Δt(10)
where dx/dθ is the derivative of x with respect to θ, and dθ/dt is the derivative of θ with respect to t.
Δt=Δx/Ω*1/v(11)
where 1/v is expressed as the following Equation 12.
1/v=dθ/dx(12)

When the scanning time difference Δt between the neighboring spots is calculated through the above process, the scanning period and beam energy determination unit270calculates the rotation angle amount Δθ of the rotating mirror240for the calculated Δt using the uniform angular velocity Ω of the rotating mirror240at step S504.

When the rotation angle amount Δθ is calculated, the scanning period and beam energy unit270updates the set initial θ value at step S505, and calculates the new scanning time difference Δt between beam spots by substituting the updated rotation angle amount Δθ for the corresponding variable of Equations 10 and 11.

By repeating the above-described process, the scanning period and beam energy determination unit270calculates the sampling time interval Δt that allows the beam scanned onto the scanning surface of the scanning object201to have uniform linear velocity.

The sampling time interval Δt calculated as described above varies with the interval between the beam spots of a beam spot arrangement on the scanning surface. The variation of the sampling time period Δt depending on the interval between the beam spots of a beam spot arrangement is shown inFIG. 6.

As shown inFIG. 6, the sampling time interval Δt gradually increases in the range from a reference beam spot that is the start point of beam scanning to a central beam spot, and gradually decreases in the range from the central beam spot to a final beam spot.

The reason why the sampling time interval Δt is determined to have time-variation is that, in the case where an F-theta lens is not employed, the interval Δt between beam spots gradually decreases in the range from the reference beam spot to the central beam spot while the interval Δt between beam spots gradually increases in the range from the central beam spot to the final beam spot, as shown inFIG. 2b. Accordingly, in accordance with the present invention, the intervals between beam spots ranging from the reference beam spot to the final beam spot are made uniform although the F-theta lens is not employed.

When the scanning period and beam energy determination unit270calculates and stores the sampling time interval Δt as described above, the control unit280retrieves and stores the sampling time interval Δt. When a beam is scanned onto the scanning object201under this condition, the control unit280operates the pixels of the light modulator230according to the stored sampling time interval Δt.

For example, if the control unit280controls the pixel operation of the light modulator230so that the operation time interval Δt between pixels for diffracting a beam spot, which is scanned onto a location near the first beam spot of a beam spot arrangement on the scanning surface, becomes 0.1 second, the control unit280controls the pixel operation of the light modulator230so that the operation time interval Δt between pixels for diffracting a beam spot, which is scanned onto a location near the central beam spot of the beam spot arrangement on the scanning surface, becomes 1 second. Furthermore, the control unit280controls the pixel operation of the light modulator230so that the operation time interval Δt between pixels for diffracting a beam spot, which is scanned onto a location near the final beam spot of the beam spot arrangement on the scanning surface, becomes 0.1 second.

When the pixels are controlled as described above, the operation time interval Δt between pixels for diffracting a beam spot, which is scanned onto a location near the central beam spot of the beam spot arrangement on the scanning surface, gradually increases from 0.1 second to 1 second in the range from the first pixel of the beam spot arrangement to the central pixel, while the operation time interval Δt gradually decreases from 1 second to 0.1 second in the range from the central spot of the beam spot arrangement to the final beam spot.

However, when the operation time interval between the pixels of the light modulator230is controlled to be different, the scanning time of a beam spot, which is scanned onto the scanning surface of the scanning object, varies, so that a printer or image display is problematic in that printing density and resolution vary.

With a printer taken as an example, the scanning time of a specific beam spot increases in proportion to the scanning time difference Δt between beam spots on the scanning surface, so that the beam energy of the scanned beam spot increases, thus increasing the printing density on the part of the scanning surface. That is, the beam energy of a beam spot is inversely proportional to the scanning time of the beam spot, so that the printing density on the corresponding part of the scanning surface decreases relatively.

In order to solve the above-described problem, the present invention controls beam energy according the scanning time difference Δt between beam spots on a scanning surface as described below.

FIG. 7is a flowchart showing a process of calculating beam energy in a light beam scanning apparatus in accordance with the present invention.

Referring toFIG. 7, the scanning period and beam energy determination unit270determines the shortest one Δtmin of all calculated scanning time differences Δt by executing Equation 11 at step S701.
R=Δtmin/Δt(13)

Thereafter, the scanning period and beam energy determination unit270determines the diffraction amounts of beams, which form beam spots on the scanning surface, by multiplying the maximum beam energy Rmax by weights for the intervals of the beam spots at step S703.
P=R*Pmax  (14)
where Pmax is the maximum output value of the light source.

When the diffraction amounts of beams, which will be scanned onto the scanning surface, are calculated as described above, the scanning period and beam energy determination unit270stores the calculated diffraction amounts P, and the control unit280reads and store the diffraction amounts P. When a beam is scanned onto the scanning object201under this condition, the control unit280controls the diffraction amounts of the pixels of the light modulator according to the stored diffraction amounts P. In this case, the amount of the pixels of the light modulator230is maximized when the height difference between the pixels is λ/4. As the height difference decreases from λ/4, the diffraction amount of the pixels decreases.

Since the height difference between the pixels increase or decreases in proportion to the amount of driving voltage, the control unit280controls the amount of voltage, which will be applied to a pixel, according to the stored diffraction amounts P.

For example, since the first beam spot of the beam spot arrangement is scanned for a relatively short time, the control unit280applies high voltage so that the diffraction amount of a corresponding pixel is maximized. In contrast, since the central beam spot of the beam spot arrangement is scanned for a relatively long time, the control unit280applies low voltage so that the diffraction amount of a corresponding pixel is minimized.

The variation in the diffraction amount of the pixels of the light modulator230, which is controlled through the above-described process, is shown inFIG. 8.

As shown inFIG. 8, since the first and last beam spots of the beam spot arrangement are scanned for a relatively long time, the diffraction amount of a corresponding pixel increases. In contrast, when a central beam spot is scanned for a long scanning time, the diffraction amount of the corresponding pixel decreases.

The control unit180makes beam energy, which will be scanned onto the scanning surface, uniform by controlling the diffraction amounts of pixels, as shown inFIG. 9.

As described above, the present invention provides a method of controlling beam scanning timing and beam energy and the light beam scanning apparatus using the same, which keeps the interval between beam spots uniform and makes beam energy distribution uniform through the automatic control of beam scanning timing and beam energy, thus simplifying the manufacture of the light beam scanning apparatus and reducing the manufacturing costs of the light beam scanning apparatus.