Patent Description:
A light scanning device that performs Lissajous scanning by irradiating a movable mirror which swings about two orthogonal axes, with light which is subjected to intensity modulation in accordance with an input image has been known. The movable mirror is resonantly driven by two sine waves having different frequencies. In the Lissajous scanning, the movable mirror is resonantly driven about the two axes. Thus, a deflection angle is large, and an advantage of increasing a scanning range of light is achieved.

In a case where the input image is drawn by the light scanning device, it is required to periodically perform light scanning in accordance with a frame period of the input image. <CIT> discloses providing an origin signal generation portion that generates an origin signal for defining a period of the Lissajous scanning, and driving the movable mirror and controlling a light emission timing of a light emitting device based on the origin signal generated by the origin signal generation portion.

However, in a case of performing the Lissajous scanning using the origin signal as disclosed in <CIT>, a deviation may occur between an origin position (for example, a center of the scanning range) indicated by the origin signal within the scanning range and an actual scanning position in a case where the origin signal generation portion has generated the origin signal. In a case where a deviation occurs between the origin position and the actual scanning position, a deviation occurs between the period of the Lissajous scanning and the light emission timing, and distortion occurs in the drawn image. In the Lissajous scanning, light is scanned to draw a complicated Lissajous curve unlike that in general raster scanning. Thus, in a case where a deviation occurs between the scanning period and the light emission timing, significant distortion occurs in the drawn image. Further prior art is known from <CIT>.

An object of the disclosed technology is to provide a control device, an image forming apparatus, and a control method that can suppress a deviation between a scanning period and a light emission timing.

In order to achieve the object, a control device according to an aspect of the present disclosure is a control device that controls a light scanning device which performs Lissajous scanning of light by irradiating a movable mirror which swings about a first axis and about a second axis, with light which is subjected to intensity modulation in accordance with an input image, the control device comprising a first measurement portion that measures, as a first elapsed time, an elapsed time from a first reference point at which a deflection angle of the movable mirror about the first axis becomes equal to a first reference angle, a second measurement portion that measures, as a second elapsed time, an elapsed time from a second reference point at which a deflection angle of the movable mirror about the second axis becomes equal to a second reference angle, an information storage portion in which intensity information representing a correspondence relationship between the first elapsed time and the second elapsed time, and a signal intensity of the input image is stored, a readout portion that reads out the signal intensity corresponding to the first elapsed time measured by the first measurement portion and to the second elapsed time measured by the second measurement portion from the information storage portion, and a light emission control portion that causes a light emitting device to perform the intensity modulation of the light based on the signal intensity read out by the readout portion.

It is preferable that the first measurement portion and the second measurement portion measure the first elapsed time and the second elapsed time, respectively, by counting a clock signal output from a clock generator.

It is preferable that the control device further comprises a first reference point detection portion that detects the first reference point, and a second reference point detection portion that detects the second reference point.

It is preferable that the light scanning device includes a first angle sensor that outputs a first angle signal corresponding to the deflection angle of the movable mirror about the first axis, and a second angle sensor that outputs a second angle signal corresponding to the deflection angle of the movable mirror about the second axis, the first reference point detection portion detects the first reference point based on the first angle signal output from the first angle sensor, and the second reference point detection portion detects the second reference point based on the second angle signal output from the second angle sensor.

It is preferable that the intensity information represents a correspondence relationship between a combination of the first elapsed time and the second elapsed time, and the signal intensity of the input image.

It is preferable that the control device further comprises a scanning path changing portion that changes a scanning path of the Lissajous scanning by changing a frequency of at least one of the swing of the movable mirror about the first axis or the swing of the movable mirror about the second axis.

It is preferable that the control device further comprises a scanning path changing portion that changes a scanning path of the Lissajous scanning by changing a phase difference between the swing of the movable mirror about the first axis and the swing of the movable mirror about the second axis.

It is preferable that the control device further comprises a scanning path changing portion that changes a scanning path of the Lissajous scanning by changing an amplitude of at least one of the swing of the movable mirror about the first axis or the swing of the movable mirror about the second axis.

It is preferable that the control device further comprises a scanning path changing portion that changes a scanning path of the Lissajous scanning based on a combination of at least two of changing a frequency of at least any one of the swing of the movable mirror about the first axis or the swing of the movable mirror about the second axis, changing a phase difference between the swing of the movable mirror about the first axis and the swing of the movable mirror about the second axis, and changing an amplitude of at least any one of the swing of the movable mirror about the first axis or the swing of the movable mirror about the second axis.

It is preferable that a scanning period of the Lissajous scanning is longer than a frame period of the input image.

An image forming apparatus according to another aspect of the present disclosure comprises any of the control devices, a light scanning device, and a light emitting device.

A control method according to still another aspect of the present disclosure is a control method of controlling a light scanning device which performs Lissajous scanning of light by irradiating a movable mirror which swings about a first axis and about a second axis, with light which is subjected to intensity modulation in accordance with an input image, the control method comprising first measurement processing of measuring, as a first elapsed time, an elapsed time from a first reference point at which a deflection angle of the movable mirror about the first axis becomes equal to a first reference angle, second measurement processing of measuring, as a second elapsed time, an elapsed time from a second reference point at which a deflection angle of the movable mirror about the second axis becomes equal to a second reference angle, readout processing of reading out, from an information storage portion in which intensity information representing a correspondence relationship between the first elapsed time and the second elapsed time, and a signal intensity of the input image is stored, the signal intensity corresponding to the first elapsed time measured by the first measurement processing and to the second elapsed time measured by the second measurement processing, and light emission control processing of causing a light emitting device to perform the intensity modulation of the light based on the signal intensity read out by the readout processing.

According to the disclosed technology, it is possible to provide a control device, an image forming apparatus, and a control method that can suppress a deviation between a scanning period and a light emission timing.

Hereinafter, embodiments according to the disclosed technology will be described in detail with reference to the drawings. As an example, in each of the following embodiments, the disclosed technology will be described in the form of being applied to an image forming apparatus that forms an image on a projection surface by scanning laser light using a Lissajous method.

<FIG> illustrates an example of a configuration of an image forming apparatus <NUM> of the present embodiment. As illustrated in <FIG>, the image forming apparatus <NUM> of the present embodiment comprises a control device <NUM>, a micro electro mechanical systems (MEMS) driver <NUM>, a light emitting device <NUM>, a multiplexing optical system <NUM>, a collimator <NUM>, and a MEMS mirror <NUM>. The MEMS mirror <NUM> is an example of a "light scanning device" according to the embodiment of the disclosed technology.

The light emitting device <NUM> includes a laser driver <NUM> and a laser light source <NUM>. The laser driver <NUM> of the present embodiment outputs laser light for forming an image from the laser light source <NUM> by driving the laser light source <NUM> based on an intensity modulation signal supplied from the control device <NUM>. For example, the laser light source <NUM> outputs the laser light of three colors of red (R), green (G), and blue (B).

The laser light output from the laser light source <NUM> is multiplexed by the multiplexing optical system <NUM>. Then, the MEMS mirror <NUM> is irradiated with the multiplexed laser light through the collimator <NUM>. The laser light condensed in the MEMS mirror <NUM> is reflected toward a projection surface <NUM> by the MEMS mirror <NUM>. For example, the projection surface <NUM> is a screen for projecting the image, or a retina of an eye of a person. That is, the image forming apparatus <NUM> of the present embodiment is used for a projector, augmented reality (AR) glasses, and the like.

In the present embodiment, the projection surface <NUM> is not limited to a surface of an actual object such as the screen and includes an imaginary plane in a space.

The MEMS driver <NUM> drives the MEMS mirror <NUM> under control of the control device <NUM>. In the MEMS mirror <NUM>, a mirror portion <NUM> (refer to <FIG>) that reflects the laser light independently swings about each of two axes orthogonal to each other as a central axis. In the present embodiment, the laser light is scanned in a state of drawing a Lissajous curve on the projection surface <NUM> by the swing of the mirror portion <NUM> based on a driving signal. The Lissajous curve is a curve that is determined by a swing frequency about a first axis, a swing frequency about a second axis, and a phase difference therebetween. The mirror portion <NUM> is an example of a "movable mirror" according to the embodiment of the disclosed technology.

The control device <NUM> of the present embodiment includes a field programmable gate array (FPGA) 20A and a memory 20B. For example, the memory 20B is a volatile memory and stores various information such as an image signal representing the image projected to the projection surface <NUM>. For example, the memory 20B stores the image signal input from an outside of the image forming apparatus <NUM>.

<FIG> illustrates an example of a configuration of the MEMS mirror <NUM>. The MEMS mirror <NUM> includes the mirror portion <NUM>, a first support portion <NUM>, a first movable frame <NUM>, a second support portion <NUM>, a second movable frame <NUM>, a connecting portion <NUM>, and a fixed frame <NUM>.

The mirror portion <NUM> has a reflecting surface 40A on which an incidence ray is reflected. For example, the reflecting surface 40A is formed with a thin metal film of gold (Au), aluminum (Al), silver (Ag), or a silver alloy. For example, a shape of the reflecting surface 40A is a circular shape.

The first support portion <NUM> is disposed outside the mirror portion <NUM> at each of positions that face each other with a second axis a<NUM> interposed therebetween. The first support portions <NUM> are connected to the mirror portion <NUM> on a first axis a<NUM> and support the mirror portion <NUM> in a swingable manner about the first axis a<NUM>.

The first movable frame <NUM> is a rectangular frame surrounding the mirror portion <NUM> and is connected to the mirror portion <NUM> through the first support portions <NUM> on the first axis a<NUM>. A piezoelectric element <NUM> is formed on the first movable frame <NUM> at each of positions that face each other with the first axis a<NUM> interposed therebetween. In such a manner, a pair of first actuators <NUM> are configured by forming two piezoelectric elements <NUM> on the first movable frame <NUM>.

The pair of first actuators <NUM> are disposed at positions that face each other with the first axis a<NUM> interposed therebetween. The first actuators <NUM> cause the mirror portion <NUM> to swing about the first axis a<NUM> by applying rotational torque about the first axis a<NUM> to the mirror portion <NUM>.

The second support portion <NUM> is disposed outside the first movable frame <NUM> at each of positions that face each other with the first axis a<NUM> interposed therebetween. The second support portions <NUM> are connected to the first movable frame <NUM> on the second axis a<NUM> and support the first movable frame <NUM> and the mirror portion <NUM> in a swingable manner about the second axis a<NUM>. In the present embodiment, the second support portions <NUM> are torsion bars that stretch along the second axis a<NUM>.

The second movable frame <NUM> is a rectangular frame surrounding the first movable frame <NUM> and is connected to the first movable frame <NUM> through the second support portions <NUM> on the second axis a<NUM>. The piezoelectric element <NUM> is formed on the second movable frame <NUM> at each of positions that face each other with the second axis a<NUM> interposed therebetween. In such a manner, a pair of second actuators <NUM> are configured by forming two piezoelectric elements <NUM> on the second movable frame <NUM>.

The pair of second actuators <NUM> are disposed at positions that face each other with the second axis a<NUM> interposed therebetween. The second actuators <NUM> cause the mirror portion <NUM> to swing about the second axis a<NUM> by applying rotational torque about the second axis a<NUM> to the mirror portion <NUM> and to the first movable frame <NUM>.

The connecting portion <NUM> is disposed outside the second movable frame <NUM> at each of positions that face each other with the first axis a<NUM> interposed therebetween. The connecting portions <NUM> are connected to the second movable frame <NUM> on the second axis a<NUM>.

The fixed frame <NUM> is a rectangular frame surrounding the second movable frame <NUM> and is connected to the second movable frame <NUM> through the connecting portions <NUM> on the second axis a<NUM>.

In addition, the first movable frame <NUM> is provided with a first angle sensor <NUM> near the first support portion <NUM>. The first angle sensor <NUM> is composed of a piezoelectric element and outputs a signal by converting a force applied by deformation of the first support portion <NUM> caused by the swing of the mirror portion <NUM> about the first axis a<NUM> into a voltage. That is, the first angle sensor <NUM> outputs a signal (hereinafter, referred to as a first angle signal) SA1 representing a deflection angle of the mirror portion <NUM> about the first axis a<NUM>. The first angle signal SA1 is a sine wave having a swing frequency of the mirror portion <NUM> about the first axis a<NUM>.

In addition, the second movable frame <NUM> is provided with a second angle sensor <NUM> near the second support portion <NUM>. The second angle sensor <NUM> is composed of a piezoelectric element and outputs a signal by converting a force applied by deformation of the second support portion <NUM> caused by the swing of the mirror portion <NUM> about the second axis a<NUM> into a voltage. That is, the second angle sensor <NUM> outputs a signal (hereinafter, referred to as a second angle signal) SA2 representing a deflection angle of the mirror portion <NUM> about the second axis a<NUM>. The second angle signal SA2 is a sine wave having a swing frequency of the mirror portion <NUM> about the second axis a<NUM>.

In the present embodiment, the first axis a<NUM> and the second axis a<NUM> are orthogonal to each other. In the following description, a direction parallel to the first axis a<NUM> will be referred to as an X direction, a direction parallel to the second axis a<NUM> will be referred to as a Y direction, and a direction orthogonal to the first axis a<NUM> and to the second axis a<NUM> will be referred to as a Z direction.

<FIG> illustrates an example of a functional configuration of the control device <NUM>. As illustrated in <FIG>, the control device <NUM> is composed of an image input portion <NUM>, an image storage portion <NUM>, an information generation portion <NUM>, an information storage portion <NUM>, a first reference point detection portion 64A, a second reference point detection portion 64B, a first measurement portion 65A, a second measurement portion 65B, a readout portion <NUM>, and a light emission control portion <NUM>. These functional portions are implemented by operating the FPGA 20A and the memory 20B in cooperation with each other.

Image data DT that represents the image to be formed is input into the image input portion <NUM> from the outside. Hereinafter, the image corresponding to the image data DT input into the image input portion <NUM> may be referred to as an input image. As an example, in the present embodiment, the image data DT of colors represented by RGB signals is input into the image input portion <NUM>. The image data DT input into the image input portion <NUM> is output to the image storage portion <NUM>. The image storage portion <NUM> is a memory that stores the image data DT output from the image input portion <NUM>. The image data DT input into the image input portion <NUM> is not limited to the present embodiment and may be data corresponding to the image to be formed. For example, the data may be binarized data that represents whether or not to output the laser light. In addition, for example, the image data DT may be data that represents multiple values of an output intensity.

The information generation portion <NUM> generates intensity information SI representing a correspondence relationship between a first count value Cx and a second count value Cy, described later, and a signal intensity of the input image. In a case where the input image is a color image, the signal intensity represents an intensity of each of the RGB signals. The information storage portion <NUM> is a memory that stores the intensity information SI generated by the information generation portion <NUM>. The first count value Cx is an example of a "first elapsed time" according to the present embodiment. The second count value Cy is an example of a "second elapsed time" according to the present embodiment.

As illustrated in <FIG>, the first reference point detection portion 64A detects a first reference point P1 based on the first angle signal SA1 output from the first angle sensor <NUM>. The first reference point P1 is a time at which the deflection angle of the mirror portion <NUM> about the first axis a<NUM> becomes equal to a first reference angle θ1. In the present embodiment, the first reference angle θ1 is set to <NUM>°. The first reference angle θ1 is not limited to <NUM>° and may be an angle at which the deflection angle has a maximum value or a minimum value.

The first reference point detection portion 64A generates a pulse signal PS1 in accordance with detection of the first reference point P1. The pulse signal PS1 in a case of θ1 = <NUM>° is a so-called zero cross signal. In the present embodiment, the first reference point detection portion 64A detects, as the first reference point P1, a time at which the deflection angle of the mirror portion <NUM> about the first axis a<NUM> becomes equal to <NUM>° during its change from a negative value to a positive value. The first reference point detection portion 64A outputs the pulse signal PS1 to the first measurement portion 65A.

As illustrated in <FIG>, the second reference point detection portion 64B detects a second reference point P2 based on the second angle signal SA2 output from the second angle sensor <NUM>. The second reference point P2 is a time at which the deflection angle of the mirror portion <NUM> about the second axis a<NUM> becomes equal to a second reference angle θ2. In the present embodiment, the second reference angle θ2 is set to <NUM>°. The second reference angle θ2 is not limited to <NUM>° and may be an angle at which the deflection angle has a maximum value or a minimum value.

The second reference point detection portion 64B generates a pulse signal PS2 in accordance with detection of the second reference point P2. The pulse signal PS2 in a case of θ2 = <NUM>° is a so-called zero cross signal. In the present embodiment, the second reference point detection portion 64B detects, as the second reference point P2, a time at which the deflection angle of the mirror portion <NUM> about the second axis a<NUM> becomes equal to <NUM>° during its change from a negative value to a positive value. The second reference point detection portion 64B outputs the pulse signal PS2 to the second measurement portion 65B.

The first measurement portion 65A performs first measurement processing of measuring an elapsed time from the first reference point P1 detected by the first reference point detection portion 64A as the first count value Cx. Similarly, the second measurement portion 65B performs second measurement processing of measuring an elapsed time from the second reference point P2 detected by the second reference point detection portion 64B as the second count value Cy.

The first measurement portion 65A and the second measurement portion 65B are supplied with a clock signal CLK from a clock generator <NUM>. The clock generator <NUM> generates the clock signal CLK having a sufficiently shorter clock period than a swing period T1 (hereinafter, referred to as a first swing period T1) of the mirror portion <NUM> about the first axis a<NUM> and a swing period T2 (hereinafter, referred to as a second swing period T2) of the mirror portion <NUM> about the second axis a<NUM>. For example, the clock signal CLK is a system clock signal supplied to each portion in the control device <NUM>.

The first measurement portion 65A uses, as the first count value Cx, a count value obtained by counting up the clock signal CLK from the first reference point P1 based on the pulse signal PS1 output from the first reference point detection portion 64A. The first measurement portion 65A resets the count value to zero for each first swing period T1 in synchronization with the pulse signal PS1.

The second measurement portion 65B uses, as the second count value Cy, a count value obtained by counting up the clock signal CLK from the second reference point P2 based on the pulse signal PS2 output from the second reference point detection portion 64B. The second measurement portion 65B resets the count value to zero for each second swing period T2 in synchronization with the pulse signal PS2.

Each of the first count value Cx measured by the first measurement portion 65A and the second count value Cy measured by the second measurement portion 65B is supplied to the readout portion <NUM>. The readout portion <NUM> performs readout processing of reading out a signal intensity corresponding to the first count value Cx and the second count value Cy, which are supplied from the first measurement portion 65A and the second measurement portion 65B, from the intensity information SI stored in the information storage portion <NUM>. The readout portion <NUM> supplies the signal intensity read out from the intensity information SI to the light emission control portion <NUM>.

The light emission control portion <NUM> performs light emission control processing of causing the light emitting device <NUM> to perform intensity modulation of the laser light based on the signal intensity supplied from the readout portion <NUM>. Specifically, the intensity modulation is performed by the laser driver <NUM>. The laser light having an intensity corresponding to the signal intensity supplied from the readout portion <NUM> is output from the laser light source <NUM>. In a case where the input image is a color image, the laser light is subjected to the intensity modulation for each color of RGB.

The first reference point detection portion 64A, the second reference point detection portion 64B, the first measurement portion 65A, the second measurement portion 65B, the readout portion <NUM>, and the light emission control portion <NUM> operate for each clock period of the clock signal CLK. That is, the laser light is subjected to the intensity modulation for each clock period in accordance with the first count value Cx and with the second count value Cy.

As illustrated in <FIG>, in the present embodiment, the MEMS driver <NUM> drives the MEMS mirror <NUM> such that a ratio of the first swing period T1 and the second swing period T2 is <NUM>:<NUM> (that is, a frequency ratio is <NUM>:<NUM>). That is, the frequency ratio of the driving signal provided to the first actuator <NUM> and to the second actuator <NUM> is set to <NUM>:<NUM>.

In the present embodiment, the laser light emitted from the light emitting device <NUM> is scanned to draw a Lissajous curve <NUM> having a shape of an eight centered at an origin K on the projection surface <NUM> by the MEMS mirror <NUM>. That is, the Lissajous curve <NUM> represents a scanning path of Lissajous scanning. The origin K is a position at which θ1 = θ2 = <NUM>° is established. In the present embodiment, the frequency ratio of the driving signal is set to <NUM>:<NUM> for simplification of description. The frequency ratio and the phase difference of the driving signal are preferably determined to increase a scanning period TL of the Lissajous scanning and to further densify the Lissajous curve <NUM>. The scanning period TL is the least common multiple of the first swing period T1 and the second swing period T2. In the present embodiment, TL = T2 is established.

Next, information generation processing performed by the information generation portion <NUM> will be described using <FIG>. The information generation portion <NUM> generates the intensity information SI based on a correspondence relationship between a path of the Lissajous curve <NUM> represented by the first count value Cx and by the second count value Cy and the signal intensity of the input image.

As illustrated in <FIG>, in the present embodiment, a rectangular scanning region <NUM> including the Lissajous curve <NUM> is divided into eight parts. Specifically, the scanning region <NUM> is divided into four parts in the X direction and into two parts in the Y direction. Each of partial regions R into which the scanning region <NUM> is divided corresponds to a scanning length of two periods of the clock period in each of the X direction and the Y direction. In the present embodiment, one line constituting the Lissajous curve <NUM> intersects with each of the partial regions R. For example, in the present embodiment, the image is formed by emitting the laser light after the intensity modulation once in each partial region R. That is, the partial regions R correspond to pixels (drawing units) of the image formed on the projection surface <NUM>.

Each of the partial regions R is defined using the first count value Cx and the second count value Cy. <FIG> is a diagram in which the partial region R is divided into a plurality of unit regions R0 in units of clock periods. In the Lissajous scanning, a scanning position reciprocates in each of the X direction and the Y direction. Thus, the scanning position passes through the unit region R0 in four passage directions along a forward path and a backward path with respect to each of the X direction and the Y direction. Here, the forward path refers to a path of movement in a direction away from the origin K, and the backward path refers to a path of movement in a direction toward the origin K.

In (Cx, Cx) illustrated in <FIG>, Cx on the left side represents the first count value Cx on the forward path, and Cx on the right side represents the first count value Cx on the backward path. Similarly, in (Cy, Cy), Cy on the left side represents the second count value Cy on the forward path, and Cy on the right side represents the second count value Cy on the backward path.

<FIG> is a diagram in which each partial region R constituting the scanning region <NUM> is represented by the plurality of unit regions R0. Each partial region R is represented using the first count value Cx and the second count value Cy. Out of two parentheses shown in each partial region R, the parenthesis in the upper part represents (Cx, Cx), and the parenthesis in the lower part represents (Cy, Cy).

<FIG> illustrates an example of a signal intensity I constituting the image data DT. The information generation portion <NUM> divides the image data DT as the input image into parts that correspond to each partial region R constituting the scanning region <NUM>. Next, the information generation portion <NUM> obtains the signal intensity I for each divided region into which the image data DT is divided. For example, the signal intensity I is obtained by averaging a plurality of pixel signals included in the divided region for each color of RGB. The signal intensity I represents the intensity of each of RGB signals. In the present embodiment, eight signal intensities I1 to I8 are obtained from the image data DT.

<FIG> illustrates an example of the intensity information SI. The information generation portion <NUM> generates the intensity information SI by associating the signal intensity I with the first count value Cx and with the second count value Cy. In the present embodiment, the information generation portion <NUM> generates the intensity information SI by associating each of the signal intensities I1 to I8 obtained from the image data DT with the first count value Cx and the second count value Cy of the corresponding partial region R.

The intensity information SI is represented as a matrix table having the first count value Cx and the second count value Cy as parameters and holds the signal intensity I corresponding to all combinations of the first count value Cx and the second count value Cy. Thus, the intensity information SI can be used in common even in a case where a relationship between the first reference point P1 and the second reference point P2 changes and where the phase difference between the first angle signal SA1 and the second angle signal SA2 changes.

In a case where the image data DT is video data composed of a plurality of frames, the information generation portion <NUM> may change the signal intensity I in the intensity information SI for each frame in accordance with an image represented by each frame. In the present embodiment, a frame period TF and the scanning period TL are set to be the same.

<FIG> illustrates an example of the readout processing performed by the readout portion <NUM>. The first count value Cx and the second count value Cy are input into the readout portion <NUM> from the first measurement portion 65A and from the second measurement portion 65B for each clock period of the clock signal CLK. <FIG> illustrates a case where each of the first count value Cx and the second count value Cy input into the readout portion <NUM> is "<NUM>". In this case, the readout portion <NUM> reads out the signal intensity I6 from the intensity information SI stored in the information storage portion <NUM> as the signal intensity I corresponding to Cx = <NUM> and to Cy = <NUM>.

The light emission control portion <NUM> causes the light emitting device <NUM> to perform the intensity modulation of the laser light based on the signal intensity I6 read out by the readout portion <NUM>.

As described above, the control device <NUM> measures, as the first count value Cx (first elapsed time), the elapsed time from the first reference point P1 at which the deflection angle of the mirror portion <NUM> about the first axis a<NUM> becomes equal to the first reference angle θ1, and measures, as the second count value Cy (second elapsed time), the elapsed time from the second reference point P2 at which the deflection angle of the mirror portion <NUM> about the second axis a<NUM> becomes equal to the second reference angle θ2. The control device <NUM> acquires the signal intensity I corresponding to the measured first count value Cx and to the measured second count value Cy from the intensity information SI and causes the light emitting device <NUM> to perform the intensity modulation of the laser light.

Accordingly, the control device <NUM> is not required to generate an origin signal for defining the scanning period TL of the Lissajous scanning unlike that in the related art. The scanning period TL may change because of effects of rotational moment of the mirror portion <NUM>, gravity, atmospheric pressure, and the like. However, according to the disclosed technology, since a light emission timing is controlled based on the first elapsed time and on the second elapsed time without using the origin signal, a deviation between the scanning period TL and the light emission timing can be suppressed even in a case where the scanning period changes.

In addition, the control device <NUM> measures the first elapsed time and the second elapsed time independently of each other. Thus, according to the disclosed technology, it is possible to perform robust image formation that is not affected by a change in the phase difference between the swing of the mirror portion <NUM> about the first axis a<NUM> and the swing of the mirror portion <NUM> about the second axis a<NUM>. In addition, according to the disclosed technology, since it is not required to correct the driving signal to maintain the phase difference to be constant, the swing frequency, the frequency ratio, the phase difference, or an amplitude about the two axes can be dynamically changed even in the middle of the Lissajous scanning. Accordingly, a resolution, a frame rate, an angle of view, a light quantity, and the like of the image formed on the projection surface <NUM> can be dynamically switched.

While the MEMS driver <NUM> drives the MEMS mirror <NUM> such that the scanning position of the laser light draws the Lissajous curve <NUM> having a shape of an eight in the embodiment, the MEMS mirror <NUM> may be driven to draw the Lissajous curve <NUM> that is denser as illustrated in <FIG> as an example. Densifying the Lissajous curve <NUM> can increase the resolution of the image formed on the projection surface <NUM>.

In addition, while the scanning region <NUM> is divided such that one line constituting the Lissajous curve <NUM> intersects with each of the partial regions R in the embodiment, the scanning region <NUM> may be divided such that two or more lines constituting the Lissajous curve <NUM> intersect with each of the partial regions R. In the example illustrated in <FIG>, two or more lines constituting the Lissajous curve <NUM> intersect with each of the partial regions R.

<FIG> illustrates an example in which four lines 70A to 70D intersect with the partial region R. The four lines 70A to 70D illustrated in <FIG> constitute one Lissajous curve <NUM> as a whole. In this case, the intensity modulation of the laser light is performed with the same signal intensity I in a case where the scanning position passes through the partial region R illustrated in <FIG> along each of the four lines 70A to 70D.

Specifically, the intensity modulation of the laser light is performed with the same signal intensity I within a time range of Cx = <NUM> and <NUM> ≤ Cy ≤ <NUM> through which the scanning position passes along the line 70A, a time range of <NUM> ≤ Cx ≤ <NUM> and <NUM> ≤ Cy ≤ <NUM> through which the scanning position passes along the line 70B, a time range of Cx = <NUM> and <NUM> ≤ Cy ≤ <NUM> through which the scanning position passes along the line 70C, and a time range of Cx = <NUM> and <NUM> ≤ Cy ≤ <NUM> through which the scanning position passes along the line 70D.

In addition, while a case where the laser light is scanned perpendicular to the planar projection surface <NUM> is assumed in the embodiment, the projection surface <NUM> that is inclined is also considered. In this case, the Lissajous curve <NUM> drawn by the laser light scanned to the projection surface <NUM> deforms as illustrated in <FIG> as an example. In a case where the Lissajous curve <NUM> deforms, the information generation portion <NUM> may generate the intensity information SI based on the deformed Lissajous curve <NUM>.

Next, a second embodiment will be described. <FIG> illustrates an example of a functional configuration of the control device <NUM> according to the second embodiment. The functional configuration of the control device <NUM> according to the second embodiment includes a scanning path changing portion <NUM> in addition to the functional configuration of the control device <NUM> according to the first embodiment. The scanning path changing portion <NUM> changes the scanning path of the Lissajous scanning with the laser light by controlling the driving signal for driving the MEMS mirror <NUM> via the MEMS driver <NUM>. That is, the scanning path changing portion <NUM> changes a shape or a size of the Lissajous curve <NUM>.

For example, the scanning path changing portion <NUM> changes the scanning path for each frame period TF. In this case, the scanning path is switched for each frame period TF, and the current scanning path passes through a region through which the previous scanning path does not pass. Thus, the scanning in the scanning region <NUM> can be densified. Consequently, the resolution of the image formed on the projection surface <NUM> is further improved.

The information storage portion <NUM> stores the intensity information SI corresponding to each of two or more scanning paths changed by the scanning path changing portion <NUM>. The readout portion <NUM> reads out the signal intensity I from the intensity information SI corresponding to the scanning path changed by the scanning path changing portion <NUM>.

As a first example, the scanning path changing portion <NUM> changes the scanning path of the Lissajous scanning by changing a frequency of at least one of the swing of the mirror portion <NUM> about the first axis a<NUM> or the swing of the mirror portion <NUM> about the second axis a<NUM> (that is, by changing the frequency ratio). As illustrated in <FIG> as an example, the scanning path changing portion <NUM> changes the frequency ratio between <NUM>:<NUM> and <NUM>:<NUM>. Changing the Lissajous curve <NUM> in such a manner densifies the scanning in the scanning region <NUM>.

In a case where the frequency ratio is changed as illustrated in <FIG>, the scanning period TL of the Lissajous scanning changes. Thus, it is also preferable to change the frequency ratio such that the scanning period TL does not change. For example, in a case where the frequency ratio is changed between <NUM>:<NUM> and <NUM>:<NUM>, it is possible to change the scanning path while maintaining the scanning period TL to be constant.

In addition, in a case where a change in the scanning path in a case where the frequency ratio is changed is small, it is possible to use the common intensity information SI without changing the intensity information SI.

As a second example, the scanning path changing portion <NUM> changes the scanning path of the Lissajous scanning by changing the phase difference between the swing of the mirror portion <NUM> about the first axis a<NUM> and the swing of the mirror portion <NUM> about the second axis a<NUM>. As illustrated in <FIG> as an example, a phase difference ϕ is switched between <NUM>° and <NUM>° while the frequency ratio is maintained at <NUM>:<NUM>. Changing the Lissajous curve <NUM> in such a manner densifies the scanning in the scanning region <NUM>.

In a case of changing the phase difference, it is possible to change the scanning path while maintaining the scanning period TL to be constant. In addition, in a case where only the phase difference is different, it is possible to use the common intensity information SI without changing the intensity information SI as described above.

As a third example, the scanning path changing portion <NUM> changes the scanning path of the Lissajous scanning by changing the amplitude of at least one of the swing of the mirror portion <NUM> about the first axis a<NUM> or the swing of the mirror portion <NUM> about the second axis a<NUM>. As illustrated in <FIG> as an example, increasing the amplitude enlarges a scanning range (that is, enlarges the Lissajous curve <NUM>). Changing the Lissajous curve <NUM> in such a manner densifies the scanning in the scanning region <NUM>.

Since increasing the amplitude enlarges the scanning range, the light quantity per pixel of the image formed on the projection surface <NUM> is decreased relative to that before the amplitude is increased. Thus, it is preferable to increase the intensity of the laser light to compensate for the decrease in the light quantity caused by increasing the amplitude.

While the scanning path changing portion <NUM> changes the scanning path between two scanning paths in the examples illustrated in <FIG>, the disclosed technology is not limited thereto, and the scanning path may be changed among three or more scanning paths. In addition, the scanning path changing portion <NUM> may change the scanning path of the Lissajous scanning based on a combination of two or more of the frequency, the phase difference, and the amplitude.

Next, a third embodiment will be described. While the scanning period TL is matched to the frame period TF in the first embodiment, the scanning period TL is set to be longer than the frame period TF (that is, TL > TF) in the third embodiment. As illustrated in <FIG> as an example, the scanning period TL is set to be twice the frame period TF (that is, TL = <NUM> × TF).

In raster scanning, the scanning region is scanned one line at a time. Thus, in a case where TL > TF is set, drawing of the image of one frame ends in the middle of the scanning region. Thus, in a case where TL > TF is set in the raster scanning, the image of one frame cannot be displayed in the entire scanning region.

On the other hand, in the Lissajous scanning, drawing is performed to reciprocate upward, downward, leftward, and rightward in the scanning region. Thus, even in a case where TL > TF is set, the image of one frame can be drawn in the entire scanning region. For example, in a case where TL = <NUM> × TF is set, the image of one frame is drawn on the scanning path of half of the Lissajous scanning, and thus the resolution of the image displayed in one frame period TF is decreased to half. However, the image is displayed in the entire scanning region. Accordingly, in the Lissajous scanning, setting TL > TF can quickly rewrite the image and can smoothly display a video of a fast motion. In addition, in the Lissajous scanning, since the scanning is densely performed in the scanning region in one scanning period TL, a video of a small motion that is similar to a still image can be accurately displayed.

Next, a fourth embodiment will be described. While the first reference point detection portion 64A and the second reference point detection portion 64B in the control device <NUM> according to the first embodiment generate the first reference point P1 and the second reference point P2 based on the first angle signal SA1 and the second angle signal SA2, respectively, the first angle signal SA1 and the second angle signal SA2 may not be generated by the first angle sensor <NUM> and the second angle sensor <NUM>. In the fourth embodiment, as illustrated in <FIG>, an angle signal generation portion <NUM> that generates the first angle signal SA1 and the second angle signal SA2 is provided in the control device <NUM>.

The angle signal generation portion <NUM> generates the first angle signal SA1 and the second angle signal SA2 by performing operation processing of estimating the deflection angle of the mirror portion <NUM> about the first axis a<NUM> and the deflection angle of the mirror portion <NUM> about the second axis a<NUM> based on the driving signal for driving the MEMS mirror <NUM> via the MEMS driver <NUM>. The angle signal generation portion <NUM> supplies the generated first angle signal SA1 and the generated second angle signal SA2 to the first reference point detection portion 64A and the second reference point detection portion 64B, respectively. The angle signal generation portion <NUM> may generate the first angle signal SA1 and the second angle signal SA2 using a trained model that is trained by machine learning. In the present embodiment, the first angle sensor <NUM> and the second angle sensor <NUM> may not be provided in the MEMS mirror <NUM>.

The embodiments can be appropriately combined with each other without contradiction.

In the embodiments, for example, the following various processors can be used as a hardware structure of a processing unit that executes various processing of the image input portion <NUM>, the image storage portion <NUM>, the information generation portion <NUM>, the information storage portion <NUM>, the first reference point detection portion 64A, the second reference point detection portion 64B, the first measurement portion 65A, the second measurement portion 65B, the readout portion <NUM>, the light emission control portion <NUM>, and the angle signal generation portion <NUM>. The various processors include, in addition to a central processing unit (CPU) that is a general-purpose processor functioning as various processing units by executing software (program), a programmable logic device (PLD) such as the FPGA that is a processor having a circuit configuration changeable after manufacture, a dedicated electric circuit such as an application specific integrated circuit (ASIC) that is a processor having a circuit configuration dedicatedly designed to execute specific processing, and the like.

One processing unit may be composed of one of the various processors or may be composed of a combination of two or more processors of the same type or different types (for example, a combination of a plurality of FPGAs and/or a combination of a CPU and an FPGA). In addition, a plurality of processing units may be composed of one processor.

The image input portion <NUM> may be an image input processor. The image storage portion <NUM> may be a memory for image storage. The information generation portion <NUM> may be an information generation processor. The information storage portion <NUM> may be a memory for information storage. The first reference point detection portion 64A may be a first reference point detection processor. The second reference point detection portion 64B may be a second reference point detection processor. The first measurement portion 65A may be a first measurement processor. The second measurement portion 65B may be a second measurement processor. The readout portion <NUM> may be a readout processor. The light emission control portion <NUM> may be a light emission control processor. The angle signal generation portion <NUM> may be an angle signal generation processor. These processing units may be composed of one processor.

Examples of the plurality of processing units composed of one processor include, first, as represented by a computer such as a client and a server, a form in which one processor is composed of a combination of one or more CPUs and software, and the processor functions as the plurality of processing units. Second, as represented by a system on chip (SoC) or the like, a form of using a processor that implements functions of the entire system including the plurality of processing units via one integrated circuit (IC) chip is included. In such a manner, various processing units are configured using one or more of the various processors as a hardware structure.

Claim 1:
A control device that controls a light scanning device which performs Lissajous scanning of light by irradiating a movable mirror which swings about a first axis and about a second axis, with light which is subjected to intensity modulation in accordance with an input image, the control device comprising:
a first measurement portion (65A) that measures, as a first elapsed time, an elapsed time from a first reference point at which a deflection angle of the movable mirror about the first axis becomes equal to a first reference angle;
a second measurement portion (65B) that measures, as a second elapsed time, an elapsed time from a second reference point at which a deflection angle of the movable mirror about the second axis becomes equal to a second reference angle;
an information storage portion (<NUM>) in which intensity information representing a correspondence relationship between the first elapsed time and the second elapsed time, and a signal intensity of the input image is stored;
a readout portion (<NUM>) that reads out the signal intensity corresponding to the first elapsed time measured by the first measurement portion and to the second elapsed time measured by the second measurement portion from the information storage portion; and
a light emission control portion (<NUM>) that causes a light emitting device to perform the intensity modulation of the light based on the signal intensity read out by the readout portion.