JP2021018235A - Detection device - Google Patents

Abstract

To provide a small detection device capable of detecting an accurate absolute position by one head.SOLUTION: A detection device 2 is provided having one head 4 including: a light source 10; and a detection unit 20 for receiving diffraction light obtained by causing light from the light source 10 to enter two points P1 and P2 separated by at a known distance L1 on a diffraction grating and multiplexed light (interference light) obtained by causing the light from the light source 10 to enter two points (P3, P4) at least one of which is different from the two points and separated by a known distance on the diffraction grating. At least part of an interstitial distance of the grating is different in two regions between two points separated by the known distance L1. An absolute position in the diffraction grating is detected based on the multiplexed light (interference light) received by the detection unit 20.SELECTED DRAWING: Figure 5

Description

The present invention relates to a detection device that detects a position using a scale.

There is a detection device that detects a position on the scale based on the interference light obtained by irradiating the scale having a diffraction grating with light. In such a detection device, the position on the scale can be detected based on the phase information obtained corresponding to the lattice pitch of the diffraction grating. However, for example, when the power of the detection device that has been turned off is turned on, the initial position at the time of turning on the power is not determined, so that the absolute position on the scale cannot be detected.
In order to deal with this, a detection device having two displacement detection units (heads) and capable of always detecting the absolute position by using the difference of the phase information obtained from the two displacement detection units (heads) has been proposed. (See, for example, Patent Document 1).

JP-A-2014-134532

However, since the detection device described in Patent Document 1 needs to include at least two displacement detection units (heads) including a light source, a detection unit, a reflection mirror, and the like, it is difficult to miniaturize the detection device. .. Further, when the lattice pitch of the diffraction grating is represented by a polynomial of degree 2 or higher, one position cannot be determined by the difference in the phase information of the two displacement detection units (heads). Therefore, in order to always determine one absolute value, it is necessary to use more displacement detection units (heads), which causes a problem that the size of the detection device becomes larger.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a small detection device capable of detecting an accurate absolute position with one head.

In order to solve the above problems, the detection device according to one embodiment of the present invention is
Light source and
Diffraction light obtained by incident light from the light source on two points on the diffraction grating at a known distance, and two points on the diffraction grating that are at least one point different from the two points at a known distance. A detection unit that receives the combined light (interference light) of the diffracted light obtained by incident light from the light source.
Equipped with one head with
The diffraction gratings differ in the interstitial distance at least in part in two regions between two points separated by the known distance.
The absolute position in the diffraction grating is detected based on the combined light (interference light) received by the detection unit.

It is possible to provide a small detection device capable of detecting an accurate absolute position with one head.

It is a top view which shows an example of the scale with the lattice which has a strain. It is a graph which shows the correlation of the phase information obtained corresponding to the displacement amount in the X-axis direction of the scale shown in FIG. 1 and the lattice pitch. It is a side view which shows typically the detection apparatus which concerns on one Embodiment of this invention. It is a graph which shows the difference of the phase information and the difference of the difference with respect to the displacement amount by the detection device shown in FIG. It is a figure which shows typically the structure of the head which concerns on 1st Embodiment of this invention, and how light travels. It is a figure which shows typically the structure of the head which concerns on 2nd Embodiment of this invention, and the way of advancing light. It is a figure which shows typically the structure of the head which concerns on 3rd Embodiment of this invention, and the way of advancing light. It is a figure which shows typically the way of progress of P polarization in embodiment shown in FIG. 7A. It is a figure which shows typically the way of advancing S polarization in the embodiment shown in FIG. 7A. It is a figure which shows typically the structure of the head which concerns on 4th Embodiment of this invention, and the way of advancing light. It is a figure which shows typically the structure and the way of advancing light about the modification of the head which concerns on 1st Embodiment of this invention.

Hereinafter, various embodiments for carrying out the present invention will be described with reference to the drawings. In each drawing, corresponding members having the same function are designated by the same reference numerals. Although the embodiments are shown separately for convenience in consideration of the explanation of the main points or the ease of understanding, partial replacement or combination of the configurations shown in the different embodiments is possible. In the second and subsequent embodiments, the description of matters common to those of the first embodiment will be omitted, and only the differences will be described. In particular, similar actions and effects with the same configuration will not be mentioned sequentially for each embodiment.
The embodiments described below are for embodying the technical idea of the present invention, and the present invention is not limited to the following unless otherwise specified. The size and positional relationship of the members shown in the drawings may be exaggerated for the sake of clarity. In the following description, the plane of the scale placed on the horizontal plane is indicated by XY coordinates, and the height direction perpendicular to it is indicated by the Z axis.

(Detection device and control system according to one embodiment of the present invention)
First, the detection device according to one embodiment of the present invention will be described with reference to FIGS. 1 to 4. FIG. 1 is a plan view schematically showing an example of a scale provided with a grid having distortion. FIG. 2 is a graph showing the correlation between the displacement amount of the scale shown in FIG. 1 in the X-axis direction and the phase information by the grid. FIG. 3 is a side view schematically showing a detection device according to one embodiment of the present invention. FIG. 4 is a graph showing a difference in phase information and a difference in difference with respect to the displacement amount by the detection device shown in FIG.

The detection device 2 according to the present embodiment includes a head 4 and a moving mechanism 6 for moving the head 4 in the X-axis direction. The head 4 includes a light source and a detection unit. The light emitted from the light source is incident on the diffraction grating provided on the detection surface 50a which is the upper surface of the scale 50, and the diffraction grating is based on the diffraction grating including the obtained phase information or their combined wave light (interference light). The phase information or the difference of the phase information corresponding to the grating pitch of is acquired.

The control unit of the detection device 2 controls the actuator of the movement mechanism 6 to control the movement of the head 4. As the actuator of the moving mechanism 6, an actuator capable of performing precise position control by a control unit such as a stepping motor is used. As a result, the control unit can accurately grasp the displacement amount X on the scale 50 of the head 4.
In the present embodiment, the head 4 is moved by the moving mechanism 6, but the present invention is not limited to this, and the scale 50 side can be moved by the moving mechanism 6, and both the head 4 and the scale 50 are moved. You can also do it. Further, the detection device 2 does not have a moving mechanism, and the head 4 and the scale 50 may move relatively due to the moving mechanism of the equipment to which the head 4 and the scale 50 are attached.

<Scale>
A plurality of slits are formed on the detection surface 50a of the scale 50 according to the present embodiment, thereby forming a diffraction grating. Here, the case where the scale 50 has a reflection type diffraction grating is shown, but it may be on the transmission side.
A plurality of slits are formed on the detection surface 50a of the scale 50 at predetermined intervals along the X-axis direction, and in the present embodiment, the lattice pitch of the diffraction grating is second-order with respect to the coordinates. It is set so that it can be approximated by a polynomial.
With the lattice pitch of such a diffraction grating, the relationship between the displacement amount X of the head 4 in the X-axis direction and the phase information in the displacement amount X is approximated by a cubic polynomial (S = -aX ³ + bX ² + cX + d). Can be done (see Figure 2).

The diffraction pattern of the present embodiment has a pattern that becomes sparse to dense from one end in the X-axis direction toward the center and becomes dense to sparse from the center to the other end. Similarly, in the orthogonal Y-axis direction, the phase information is approximated by a third-order polynomial, and becomes sparse to dense as it progresses from one end to the center, and becomes dense to sparse as it progresses from the center to the other end. It has a diffraction grating pattern. That is, it can be said that the scale 50 according to the present embodiment includes a grid having distortion. In addition, it may have a pattern of a diffraction grating that becomes dense to sparse from one end to the center and becomes sparse to dense from the center to the other end.

A supplementary explanation of acquiring phase information corresponding to the lattice pitch of the diffraction grating based on diffracted light including phase information or their combined light (interference light) is as follows.
The diffraction grating is irradiated with light, and a signal is output based on the obtained diffracted light. For example, a signal period of 1/2 of the lattice spacing can be obtained by a two-phase sine wave generated by interfering each of the -1 and +1 order diffracted lights. Further, by using an optical system, a signal period of 1/4 of the lattice spacing can be obtained. By dividing this signal by the interpolation circuit, phase information with higher resolution can be obtained.

<Absolute position detection based on phase information>
In the present embodiment, as shown in FIG. 3, at a predetermined displacement amount X of the head 4, points P1 and P2 separated by a known distance L1 and points P3 and P4 4 separated by a known distance L1. Diffracted light having phase information at a location can be obtained. As a result, the difference in the phase information between the points 2 and 1 (P2-P1) and the difference in the phase information between the points 4 and 3 (P4-P3) can be obtained. The area between the points P1 and P2 separated by a distance L1 is referred to as a first region R1, and the area between the points P3 and P4 separated by a distance L1 is referred to as a second region R2.
In FIG. 4, the difference (P2-P1) of the phase information of the points 2 and 1 with respect to the displacement amount X is shown by a alternate long and short dash line. Similarly, the difference (P4-P3) of the phase information of the points 4 and 3 with respect to the displacement amount X is shown by a dotted line. Both are shown as curves representing a quadratic function obtained by differentiating the phase information represented by the cubic function.

In the present embodiment, in the X-axis direction, the lattice pitch of the diffraction grating changes from sparse to dense as it progresses from one end to the center, and from dense to sparse as it progresses from the center to the other end, and the phase information is third-order. It changes as shown by the polynomial.

Even if the two regions (first region R1 and second region R2) are at arbitrary positions on the diffraction grating, as long as they have a lattice pattern in which one absolute position is determined by the difference in the distance between the gratings. It is possible to provide a highly reliable detection device 2 capable of reliably detecting an absolute position on a diffraction grating. In a diffraction grating whose lattice pitch is approximated by a quadratic polynomial, it is possible to determine whether the lattice pattern is a sparse to dense region or a dense to sparse region by acquiring phase information at a constant displacement amount. In that case, one absolute position is determined by the difference in the distance between the gratings in the entire region. Considering the manufacturing cost and the like, it can be said that a lattice pattern that can be approximated by a quadratic polynomial is preferable in that it can be efficiently formed.

However, if it is not possible to determine whether the area is sparse to dense or dense to sparse, the difference value of the phase information is equidistant from the center of the grid pattern (symmetrical position). Is the same, so one absolute position cannot be determined. Therefore, in the present embodiment, the absolute position can always be detected by further taking the difference.

In FIG. 4, the difference (P4-P3) with respect to the displacement amount X and the difference ((P4-P3)-(P2-P1)) of the difference (P2-P1) are shown by solid lines. The difference of the difference is shown as a straight line representing the linear function obtained by differentiating the difference of the phase information represented by the quadratic function. Therefore, the position across the X-axis where the difference value of the difference becomes zero is the densest point of the diffraction grating having distortion. As a result, the displacement amount and phase information at the detection position and the displacement amount and phase information at the densest point of the diffraction grating can be known, so that the absolute position in the X-axis direction can always be detected based on the phase information.

As described above, the phase information of the grating is determined according to the inter-grid distance, and in the two regions (first region R1 and second region R2), the phase is generated by the diffracted light at two points separated by a known distance L1. Information is obtained, and the absolute position on the diffraction grating can be detected based on the difference in the difference due to the phase information obtained by the diffracted light. As a result, it is possible to reliably detect the absolute position on the diffraction grating using one head 4.

In particular, when the phase information by the lattice is approximated by the cubic equation and the difference of the phase information obtained by the diffracted light is approximated by the linear equation, the absolute position can be detected easily and efficiently. it can.

As described above, when the diffraction grating has a grating pattern that becomes sparse to dense as it progresses from one end to the center and becomes dense to sparse as it progresses from the center to the other end, the absolute position is detected. The scale for this can be formed efficiently.

Since the scale 50 has a similar grid pattern also in the Y-axis direction, it is possible to always detect the absolute position in the Y-axis direction based on the phase information. In the above, the case where the scale 50 is a diffraction grating having a lattice pitch that can be approximated by a second-order polynomial is taken as an example, but the scale is approximated by a third-order polynomial or a first-order polynomial if there is a change in density. It may be a diffraction grating with a possible grating pitch. The interstitial distance is different at least in part, so that the absolute position in the diffraction grating can be detected based on the diffracted light received in the two regions (first region R1 and second region R2). If possible, any grating pattern can be adopted.
A specific embodiment of the head 4 for detecting an absolute position using such a difference difference ((P4-P3)-(P2-P1)) will be described in detail below.

(Head according to the first embodiment)
First, the head according to the first embodiment of the present invention will be described with reference to FIG. FIG. 5 is a diagram schematically showing a configuration of a head and a way of traveling light according to the first embodiment of the present invention.
The head 4 according to the present embodiment includes a light source 10 and a detection unit 20 that receives the diffracted light obtained by incident the light from the light source 10 on the diffraction grating provided on the detection surface 50a of the scale 50. .. Further, the head 4 includes four mirrors 30a, 30b, 30c, 30d and two polarizing beam splitters (PBS) 40a, 40b as an optical system.
An LED or LD can be used as the light source 10, and it has an optical system such as a collimating lens and a condenser lens. The detection unit 20 can use a light receiving element such as a CCD, CMOS, or PD, and has an optical system such as a PBS, NPBS, a polarizing plate, a wave plate, a collimating lens, and a condenser lens.

The head 4 having one light source 10 and one detection unit 20 has one of the heads 4 in the first region R1 between two points (points P1 and P2) separated by a known distance L1 due to the arrangement of the optical system. The polarized light from the light source 10 (for example, P-polarized light) is incident at the point (P1), and the obtained +1st-order diffracted light is incident on the diffraction grating at the other point (P2). As a result, the first diffracted light having the phase information of P2-P1 is acquired.
Similarly, in the second region R2 between two points (points P3 and P4) separated by a known distance L1, the polarization of light from the light source 10 (for example, S polarization) is incident at one point (P3). , The obtained +1st-order diffracted light is incident on the diffraction grating at the other point (P4). As a result, the second diffracted light having the phase information of P4-P3 is acquired.

Then, the detection unit 20 receives the combined light (interference light) of the first diffracted light and the second diffracted light, and based on the difference in the phase information obtained by this, the absolute position on the scale 50 is determined. Can be detected. In the first embodiment, the points P2 and P3, that is, the first region R1 and the second region R2 are arranged apart by a known distance L2.

<How light travels>
Next, how the light travels in the head 4 according to the first embodiment will be described in detail.
Both P / S polarized light is emitted from the light source 10 in the upper left direction of the drawing (see the double-line arrow), and is incident on the polarization beam splitter (PBS) 40a. P-polarized light travels straight through the polarizing beam splitter (PBS) 40a (see solid arrow). On the other hand, S-polarized light is reflected by the polarizing beam splitter (PBS) 40a in the lower left direction of the drawing (see the arrow of the alternate long and short dash line).

<Progression of light in the first region R1>
The straight-ahead P-polarized light is reflected by the mirror 30a, travels in the lower left direction of the drawing, and is incident on the detection surface 50a of the scale 50. Then, the primary diffracted light advances in the + 1st order direction in the upper right direction of the drawing. As a result, +1st-order refracted light including the phase information at the point P1 is obtained. The 0th-order light at the point P1 is reflected in the upper left direction of the drawing, travels to the outside of the head 4, and does not enter the detection unit 20.

The + 1st-order diffracted light traveling from the detection surface 50a of the scale 50 toward the upper right of the drawing is incident on the mirror 30b in which the reflecting surface is horizontally arranged, and is reflected in the lower right direction of the drawing. The + 1st-order diffracted light reflected in the lower right direction of the drawing is incident on the detection surface 50a of the scale 50. Then, the -1st-order diffracted light of the + 1st-order diffracted light advances in the upper left direction of the drawing. As a result, diffracted light including the phase information at the point P2 can be obtained. The diffracted light including the phase information of the P-polarized point P1 and the phase information of the point P2 is referred to as a first diffracted light. The 0th-order light at the point P2 is reflected in the upper right direction of the drawing and does not enter the detection unit 20.

Since the first diffracted light traveling from the detection surface 50a of the scale 50 toward the upper left of the drawing is P-polarized light, it passes through the polarizing beam splitter (PBS) 40b. As a result, it becomes a part of the combined light (interference light) incident on the detection unit 20.

<Progression of light in the second region R2>
The S-polarized light reflected by the polarization beam splitter (PBS) 40a in the lower left direction of the drawing is incident on the detection surface 50a of the scale 50. Then, the primary diffracted light advances in the + 1st order direction in the upper right direction of the drawing. As a result, +1st-order refracted light including the phase information at the point P3 is obtained. The 0th-order light at the point P3 is reflected in the upper left direction of the drawing and does not enter the detection unit 20.

The + 1st-order diffracted light traveling from the detection surface 50a of the scale 50 toward the upper right of the drawing is incident on the mirror 30c in which the reflecting surface is horizontally arranged, and is reflected in the lower right direction of the drawing. The + 1st-order diffracted light reflected in the lower right direction of the drawing is incident on the detection surface 50a of the scale 50. Then, the -1st-order diffracted light of the + 1st-order diffracted light advances in the upper left direction of the drawing. As a result, diffracted light including the phase information at the point P4 can be obtained. The diffracted light including the phase information of the S-polarized point P3 and the phase information of the point P4 is referred to as a second diffracted light. The 0th-order light at the point P4 is reflected in the upper right direction of the drawing, travels to the outside of the head 4, and does not enter the detection unit 20.

The second diffracted light traveling from the detection surface 50a of the scale 50 toward the upper left of the drawing is reflected by the mirror 30d, travels toward the lower left of the drawing, and is incident on the polarizing beam splitter (PBS) 40b. Since the second diffracted light is S-polarized light, it is reflected by the polarizing beam splitter (PBS) 40b and becomes a part of the combined light (interference light) incident on the detection unit 20.

As described above, the first diffracted light having the phase information at the P-polarized point P1 and the phase information at the point P2, and the second diffracted light having the phase information at the S-polarized point P3 and the phase information at the point P4. The combined wave light (interference light) of the above is incident on the detection unit 20 (see the double line arrow).

Due to this combined light (interference light), the difference between the phase information at points P4 and P3 (P4-P3) and the difference between the phase information at points P2 and P1 (P2-P1). ((P4-P3)-(P2-P1)) can be obtained. The absolute position in the X-axis direction with respect to the scale 50 can be detected by using the difference of the difference of the phase information.

In this embodiment, +1st order diffracted light and − diffracted light are used, but this is an example, and second or higher order diffracted light can also be used. Further, in the present embodiment, the positive diffracted light is incident on the diffraction grating to obtain the negative diffracted light, but conversely, the negative diffracted light is incident on the diffraction grating to obtain the positive diffracted light. possible. That is, the plus or minus M (integer of M: 1 or more) next diffracted light obtained by incident polarization at one point (P1, P3) is incident on the diffraction grating at the other point (P2, P4). It is possible to obtain the first or second diffracted light of the minus or plus M order.

(Modified example of the first embodiment)
Next, a modified example of the head according to the first embodiment of the present invention will be described with reference to FIG. FIG. 9 is a diagram schematically showing a configuration and a way of traveling light regarding a modified example of the head according to the first embodiment of the present invention. In FIG. 9, the arrow indicating the 0th order light is omitted. The modified example shown in FIG. 9 differs from the first embodiment shown in FIG. 5 in the following points.

In the modified example, both P / S polarized light is emitted from the light source 10 in the left direction of the drawing, which is the direction parallel to the detection surface 50a of the scale 50 (see the double-line arrow). The P-polarized light that passes through the polarization beam splitter (PBS) 40a and travels straight to the left is reflected by the mirror 30a and travels downward in the drawing, which is the direction perpendicular to the detection surface 50a of the scale 50, and the detection surface. It is incident on 50a (see solid arrow). Therefore, the +1 primary direction in which the primary diffracted light travels from the point P1 on the detection surface 50a is a direction more angled with respect to the detection surface 50a as compared with the first embodiment shown in FIG. Therefore, since the primary diffracted light is again incident on the point P2 of the detection surface 50a which is a distance L1 away from the point P1, in the modified example, the mirror is not arranged horizontally but is angled with respect to the detection surface 50a. The primary diffracted light is reflected twice by the two mirrors 30b1 and b2, and is incident on two points on the detection surface 50a. Then, from the point P2 of the detection surface 50a, the -1st-order diffracted light of the primary diffracted light travels in the direction on the drawing, which is the direction perpendicular to the detection surface 50a, and passes through the polarizing beam splitter (PBS) 40b. It becomes a part of the combined wave light (interference light) and further advances in the upward direction of the drawing to enter the detection unit 20.

Of the P / S polarized light emitted from the light source 10 to the left in the drawing, the S polarized light reflected downward in the drawing, which is the direction perpendicular to the detection surface 50a by the polarizing beam splitter (PBS) 40a, is It is incident on the point P3 of the detection surface 50a of the scale 50 (see the arrow of the alternate long and short dash line). The +1 primary direction in which the primary diffracted light travels from the point P3 on the detection surface 50a is a direction more angled with respect to the detection surface 50a as compared with the first embodiment shown in FIG. Therefore, in order to make the primary diffracted light incident on the point P4 of the detection surface 50a which is a distance L1 away from the point P3 again, the two mirrors 30c1 and c2 which are angled with respect to the detection surface 50a make 1 The next diffracted light is reflected twice and incident on the point P4 of the detection surface 50a. Then, from the point P4 of the detection surface 50a, the -1st-order diffracted light of the primary diffracted light travels in the upward direction of the drawing, which is the direction perpendicular to the detection surface 50a, is reflected by the mirror 30d, and proceeds to the left of the drawing. .. Then, the -1st order diffracted light is reflected by the polarizing beam splitter (PBS) 40b, becomes a part of the combined wave light (interference light), and further advances in the upward direction of the drawing to enter the detection unit 20.

In the modified example shown in FIG. 9, the primary diffracted light is incident on the detection surface 50a from the direction perpendicular to the detection surface 50a for both P-polarized light and S-polarized light, and the -1st-order diffracted light of the primary diffracted light is emitted from the detection surface 50a. It emits light in a direction perpendicular to the detection surface 50a. Therefore, even if the detection surface 50a fluctuates in the vertical direction of the drawing, the -1st-order diffracted light of the primary diffracted light is the point P2 and within the range incident on the reflecting surface of the mirrors 30b1, 30b2, 30c1 and 30c2. From the point P4, it advances in the upward direction of the drawing perpendicular to the detection surface 50a and always incident on the detection unit 20 (see the dotted line). Therefore, in the modified example, even if the clearance of the detection surface 50a fluctuates, it can be absorbed and reliably detected.

(Head according to the second embodiment)
Next, the head according to the second embodiment of the present invention will be described with reference to FIG. FIG. 6 is a diagram schematically showing a configuration of a head and a way of traveling light according to a second embodiment of the present invention.
The head 4 according to the second embodiment is different from the first embodiment in that the points P2 and P3 separated by a length L2 are arranged in reverse. However, the length of the first region R1 between the points P1 and P2 and the length of the second region R2 between the points P3 and P4 are L1 as in the first embodiment described above. .. That is, in the second embodiment, a part of the first region R1 and the second region R2 are arranged so as to overlap each other.

More specifically, in the second embodiment, from the left side to the right side of the drawing, P3 is separated from P1, P1 by a length L1-L2, P2 is separated from P3 by a length L2, and P2 is a length L1-L2. P4s that are only separated from each other will be placed. The length L2 can take any value in a range smaller than L1. As a result, the values of L1-L2 are always positive values. Other points are the same as those in the first embodiment described above.

With the above arrangement, the way of the P-polarized light transmitted through the polarizing beam splitter (PBS) 40a and the S-polarized light reflected by the polarizing beam splitter (PBS) 40a is the same as that of the first embodiment. In the region between the points P2 and P3, the P-polarized light and the S-polarized light are arranged so as not to interfere with each other.
As a result, in the second embodiment as well as in the first embodiment, the difference difference (P4-P3)-(P2-P1)) can be obtained, and this can be used to obtain the X-axis with respect to the scale 50. The absolute position in the direction can be detected. In the arrangement of the second embodiment, the distance between the point P1 at the left end of the drawing and the point P4 at the right end of the drawing can be shortened by 2 × L2 as compared with the first embodiment.

(Head according to the third embodiment)
Next, the head according to the third embodiment of the present invention will be described with reference to FIGS. 7A, 7B, and 7C. FIG. 7A is a diagram schematically showing a configuration of a head and a way of traveling light according to a third embodiment of the present invention. FIG. 7B is a diagram schematically showing how P-polarized light proceeds in the embodiment shown in FIG. 7A. FIG. 7C is a diagram schematically showing how S polarization proceeds in the embodiment shown in FIG. 7A.

The head 4 according to the third embodiment is different from the first and second embodiments described above in that L2, which is the length between points P2 and P3, is 0. That is, in the third embodiment, the first region R1 and the second region R2 are connected and arranged, and the point P2 and the point P3 are the same point. However, the length of the first region R1 between the points P1 and P2 and the length of the second region R2 between the points P3 and P4 are the same as those of the first and second embodiments described above. It has become.

More specifically, in the third embodiment, P2 (P3) separated from points P1 and P1 by a length L1 and P4 separated from P3 (P2) by a length L1 are arranged from the left side to the right side of the drawing. ing. Other points are the same as those in the first and second embodiments described above.
If the arrangement of the points P1 to P4 in the first to third embodiments is described collectively, the light from the light source is incident on the diffraction grating at two points (for example, points P1 and P2) separated by a known distance L1. The light from the light source 10 is incident on the diffracted light obtained by the above and two points (for example, points P2 (= P3) and P4) separated by a known distance L1 on a diffraction grating in which at least one point is different from the two points. It can be expressed as obtaining diffracted light.

In the arrangement 2 as described above, the way of the P-polarized light transmitted through the polarizing beam splitter (PBS) 40a and the S-polarized light reflected by the polarizing beam splitter (PBS) 40a is the same as in the first and second embodiments. Is. However, when L2 = 0, as shown in FIG. 7B, the 0th-order light of P-polarized light generated at the point P2 (P3) overlaps with the optical path forming the second diffracted light of S-polarized light. However, by using a light source having a sufficiently short coherence distance, two components of orthogonally polarized light that do not interfere can be obtained. Since the 0th-order light reflected by the mirror 30d is P-polarized, it passes through the polarizing beam splitter (PBS) 40a and does not enter the detection unit 20.

Similarly, as shown in FIG. 7C, in S-polarized light, the 0th-order light of S-polarized light generated at the point P3 (P2) overlaps a part of the optical path forming the first diffracted light of P-polarized light. Become. However, by using a light source having a sufficiently short coherence distance, two components of orthogonally polarized light that do not interfere can be obtained. Since the 0th-order light generated at the point P3 (P2) is S-polarized, it is reflected by the polarizing beam splitter (PBS) 40a and does not enter the detection unit 20.

As a result, in the third embodiment as well as in the first and second embodiments, the difference difference (P4-P3)-(P2-P1)) can be obtained, and the scale 50 can be obtained by using this. It is possible to detect the absolute position in the X-axis direction with respect to. In the arrangement of the third embodiment, the distance between the point P1 at the left end of the drawing and the point P4 at the right end of the drawing can be shortened by L2 as compared with the first embodiment.

(Head according to the fourth embodiment)
Next, the head according to the fourth embodiment of the present invention will be described with reference to FIG. FIG. 8 is a diagram schematically showing a configuration of a head and a way of traveling light according to a fourth embodiment of the present invention. In the first to third embodiments described above, components (light source 10, detection unit) 20, mirrors 30a, 30b, 30c, 30d, polarizing beam splitters (PBS) 40a, 40b) are the same, but the head 4 according to the fourth embodiment has the same components as those of the first to third embodiments. different.

The head 4 according to the fourth embodiment includes two light sources 10A and 10B, and detection units 20A and 20B corresponding to the respective light sources. Further, as an optical system, a polarizing beam splitter (PBS) 40, mirrors 30a and 30b, and reflective wave plates 32a and 32b are provided on the optical path from the first light source 10A to the first detection unit 20A. Similarly, on the optical path from the second light source 10B to the second detection unit 20B, in addition to the above-mentioned polarization beam splitter (PBS) 40, mirrors 30c and 30d, and reflective wave plates 32c and 32d are provided.

The arrangement of the points P1 to P4 from which the diffracted light is obtained is the same as that of the first embodiment described above, and from the left side to the right side of the drawing, only P2 and P2 separated from P1 by length L1 and only length L2 from P2. P3, which is separated from P3, and P4, which is separated by a length L1 from P3, are arranged. That is, the first region R1 between the points P1 and P2 separated by the known distance L1 and the second region R2 between the known distance L1 separated points P3 and P4 are arranged apart by the known distance L2. Has been done.

The head 4 has a first detection unit 20A corresponding to the first light source 10A and the first light source 10A, and a second detection unit 20B corresponding to the second light source 10B and the second light source 10B. Then, the diffracted light having the phase information of + 2 kxP1 obtained by incident the light from the first light source 10A at the point P1 and the light from the first light source 10A at the point P4 are incident on the diffraction grating. The first detection unit 20A receives the combined light (interference light) of the diffracted light having the phase information of -2kxP4. Similarly, the diffracted light having the phase information of + 2kxP2 obtained by incident the light from the second light source 10B at the point P2 and the light from the second light source 10B at the point P3 are incident on the diffraction grating. The second detection unit 20B receives the combined light (interference light) of the diffracted light having the phase information of -2 kxP3. Then, the absolute position in the diffraction grating can be detected based on the difference in the phase information obtained by the difference in the detection signals by the first detection unit 20A and the second detection unit 20B.

<How light travels>
Next, how the light travels in the head 4 according to the fourth embodiment will be described in detail.
<Optical path from the light source 10A to the detection unit 20A>
Both P / S polarized light is emitted from the light source 10A in the diagonally lower left direction of the drawing (see double line), and is incident on the polarization beam splitter (PBS) 40. P-polarized light travels straight through the polarizing beam splitter (PBS) 40 (see solid arrow). On the other hand, S-polarized light is reflected by the polarizing beam splitter (PBS) 40 toward the lower right side of the drawing (see the arrow of the alternate long and short dash line).

[Point P1]
The straight P-polarized light is reflected by the mirror 30a, travels downward in the drawing, and is incident on the detection surface 50a of the scale 50. Then, the primary diffracted light advances in the + 1st order direction in the upper right direction of the drawing. As a result, +1st-order refracted light including the phase information at the point P1 is obtained. The +1st-order diffracted light traveling from the detection surface 50a of the scale 50 toward the upper right of the drawing enters the reflective wave plate 32a and is reflected in the opposite direction, the lower left of the drawing. The P-polarized light incident on the reflective wave plate 32a is reflected as S-polarized light by changing the polarization direction by 90 degrees by the reflective wave plate 32a.

The S-polarized + 1st-order diffracted light reflected by the reflective wave plate 32a in the lower left direction of the drawing is incident on the detection surface 50a of the scale 50. Then, the + 1st-order diffracted light of the + 1st-order diffracted light advances in the + 1st-order direction on the drawing. As a result, diffracted light including the phase information at the point P1 can be obtained. The diffracted light traveling from the scale 50 toward the upper side of the drawing is incident on the mirror 30a. The diffracted light reflected by the mirror 30a in the upper right direction of the drawing is incident on the polarizing beam splitter (PBS) 40. That is, the S-polarized light reflected by the reflective wave plate 32a travels in the opposite direction in the P-polarized light path transmitted through the polarizing beam splitter (PBS) 40.

Since the diffracted light incident on the polarizing beam splitter (PBS) 40 is S-polarized light, it is reflected by the polarizing beam splitter (PBS) 40 in the upper left direction of the drawing and heads toward the detection unit 20A. As a result, it becomes a part of the combined light (interference light) incident on the detection unit 20A (see the double line).

[Point P4]
The polarized beam splitter (PBS) 40 is reflected to the lower right side of the drawing, and the S polarized light is reflected by the mirror 30b, travels downward in the drawing, and is incident on the detection surface 50a of the scale 50. Then, the -1st-order diffracted light advances in the -1st-order direction in the upper left direction of the drawing. As a result, the first-order diffracted light including the phase information at the point P4 is obtained. The -1st-order diffracted light traveling from the detection surface 50a of the scale 50 toward the upper left of the drawing enters the reflective wave plate 32b and is reflected in the opposite direction, the lower right of the drawing. The S-polarized light incident on the reflective wave plate 32b is reflected as P-polarized light by changing the polarization direction by 90 degrees by the reflective wave plate 32b.

The P-polarized -1st-order diffracted light reflected by the reflective wave plate 32b in the lower right direction of the drawing is incident on the detection surface 50a of the scale 50. Then, the -1st-order diffracted light of the -1st-order diffracted light advances in the -1st-order direction on the drawing. As a result, diffracted light including the phase information at the point P4 can be obtained. The diffracted light traveling from the scale 50 toward the upper side of the drawing is incident on the mirror 30b. The diffracted light reflected by the mirror 30b in the upper left direction of the drawing is incident on the polarization beam splitter (PBS) 40. That is, the P-polarized light reflected by the reflective wave plate 32b travels in the opposite direction in the S-polarized light path transmitted through the polarizing beam splitter (PBS) 40.

Since the diffracted light incident on the polarizing beam splitter (PBS) 40 is P-polarized, it passes through the polarizing beam splitter (PBS) 40 and heads toward the detection unit 20A. As a result, it becomes a part of the combined light (interference light) incident on the detection unit 20A (see the double line).

<Optical path from light source 10B to detection unit 20B>
The optical path from the second light source 10B to the detection unit 20B is the same as described above.
Both P / S polarized light is emitted from the light source 10B in the diagonally lower left direction of the drawing (see double line), and is incident on the polarization beam splitter (PBS) 40. P-polarized light travels straight through the polarizing beam splitter (PBS) 40 (see solid arrow). On the other hand, S-polarized light is reflected by the polarizing beam splitter (PBS) 40 toward the lower right side of the drawing (see the arrow of the alternate long and short dash line).

[Point P2]
The straight P-polarized light is reflected by the mirror 30c, travels downward in the drawing, and is incident on the detection surface 50a of the scale 50. Then, the +1st-order diffracted light advances in the +1-order direction in the upper right direction of the drawing. As a result, +1st-order refracted light including the phase information at the point P2 is obtained. The + 1st-order diffracted light traveling from the detection surface 50a of the scale 50 toward the upper right of the drawing enters the reflective wave plate 32c and is reflected in the opposite direction, the lower left of the drawing. The P-polarized light incident on the reflective wave plate 32c is reflected as S-polarized light by changing the polarization direction by 90 degrees by the reflective wave plate 32c.

The S-polarized + 1st-order diffracted light reflected by the reflective wave plate 32c in the lower left direction of the drawing is incident on the detection surface 50a of the scale 50. Then, the + 1st-order diffracted light of the + 1st-order diffracted light advances in the + 1st-order direction on the drawing. As a result, diffracted light including the phase information at the point P1 can be obtained. The diffracted light traveling from the scale 50 toward the upper side of the drawing is incident on the mirror 30a. The diffracted light reflected by the mirror 30a in the upper right direction of the drawing is incident on the polarizing beam splitter (PBS) 40. That is, the S-polarized light reflected by the reflective wave plate 32a travels in the opposite direction in the P-polarized light path transmitted through the polarizing beam splitter (PBS) 40.

Since the diffracted light incident on the polarizing beam splitter (PBS) 40 is S-polarized light, it is reflected by the polarizing beam splitter (PBS) 40 in the upper left direction of the drawing and heads toward the detection unit 20B. As a result, it becomes a part of the combined light (interference light) incident on the detection unit 20B (see the double line).

[Point P3]
The polarized beam splitter (PBS) 40 is reflected to the lower right side of the drawing, and the S polarized light is reflected by the mirror 30d, travels downward in the drawing, and is incident on the detection surface 50a of the scale 50. Then, the -1st-order diffracted light advances in the -1st-order direction in the upper left direction of the drawing. As a result, the first-order diffracted light including the phase information at the point P3 is obtained. The -1st order diffracted light traveling from the detection surface 50a of the scale 50 toward the upper left of the drawing enters the reflective wave plate 32d and is reflected in the opposite direction, the lower right of the drawing. The S-polarized light incident on the reflective wave plate 32d is reflected as P-polarized light by changing the polarization direction by 90 degrees by the reflective wave plate 32d.

The P-polarized -1st-order diffracted light reflected by the reflective wave plate 32d in the lower right direction of the drawing is incident on the detection surface 50a of the scale 50. Then, the -1st-order diffracted light of the -1st-order diffracted light advances in the -1st-order direction on the drawing. As a result, diffracted light including the phase information at the point P3 can be obtained. The diffracted light traveling from the scale 50 toward the upper side of the drawing is incident on the mirror 30d. The diffracted light reflected by the mirror 30d in the upper left direction of the drawing is incident on the polarizing beam splitter (PBS) 40. That is, the P-polarized light reflected by the reflective wave plate 32d travels in the opposite direction in the S-polarized light path transmitted through the polarizing beam splitter (PBS) 40.

Since the diffracted light incident on the polarizing beam splitter (PBS) 40 is P-polarized, it passes through the polarizing beam splitter (PBS) 40 and heads toward the detection unit 20B. As a result, it becomes a part of the combined light (interference light) incident on the detection unit 20B (see the double line).

As described above, in the fourth embodiment, the first detection unit 20A that has received the combined light (interference light) including the phase information of the point P1 and the phase information of the point P4 generates the detection signal of P1 + P4. Similarly, the second detection unit 20B that receives the combined wave light (interference light) including the phase information of the point P2 and the phase information of the point P3 generates the detection signal of P2 + P3. By taking the difference between these detection signals, the information of "(P1 + P4)-(P2 + P3)" can be obtained.
When this is rewritten, it becomes "(P4-P3)-(P2-P1)", and the difference (P4-P3) in the second region R2 and the first one are the same as in the first to third embodiments described above. It is possible to obtain the difference "(P4-P3)-(P2-P1))" of the difference of the phase information, which is the difference of the difference (P2-P1) in the region R1. This can be used to detect the absolute position in the X-axis direction with respect to the scale 50.

In this embodiment, the +1st order diffracted light and the -1st order diffracted light are used, but this is an example, and the second or higher degree diffracted light can also be used. Further, the order of the diffracted light used in the optical path between the first light source 10A and the first detection unit 20A and the order of the diffracted light used in the optical path between the second light source 10B and the second detection unit 20B are determined. It can be different.
That is, the plus or minus M (an integer of M: 1 or more) next diffraction obtained by incident the polarization of the light from the first light source 10A at one point (P1), and the other point ( The first detection unit 20A receives the negative or positive Mth-order diffracted light obtained by incidenting the polarization of the light from the first light source 10A on the diffraction grating at P4), and the first detection unit 20A receives the light at one point (P2). Plus or minus N (an integer of N: 1 or more) obtained by incidently polarizing the light from the second light source 10B, and the light from the second light source 10B at the other point (P3). The second detection unit 20B receives the negative or positive Nth-order diffracted light obtained by incidenting the polarized light on the diffraction grating.

(Summary of Embodiment)
The various embodiments described above can be summarized as follows.
The detection device 2 includes a light source 10 (10A, 10B: in the case of the fourth embodiment), diffracted light obtained by incident light from the light source at two points on the diffraction grating at known distances, and the diffracted light. Detection unit 20 (20A, 20B) that receives the combined light (interference light) of the diffracted light obtained by incident the light from the light source on two points on the diffraction grating that are different from the two points at a known distance. : With one head 4 having (in the case of the fourth embodiment).
Here, the two points on the diffraction grating that are separated by a known distance correspond to the point P1 and the point P2 that are separated by a distance L1. Further, the two points separated by a known distance on the diffraction grating that differ from the two points by at least one point correspond to the point P3 (or P2: in the case of the third embodiment) and the point P4 separated by the distance L1.

The grating is at least in part in two regions between two points that are known distances L1 apart (the first region R1 between P1 and P2 and the second region R2 between P3 (P2) and P4). The distance between the gratings is different, so that the absolute position in the diffraction grating can be detected based on the combined wave light (interference light) received by the detection unit 20.
With such a configuration, it is possible to provide a compact detection device 2 capable of detecting an accurate absolute position with one head. This enables space-saving arrangement that solves problems such as electrical noise and restrictions on the mounting position.

In particular, since the same detection unit 20 (20A, 20B) receives the combined light of the light having the phase information at each diffraction point P1, P2, P3, P4 (P1 and P4, P2 and P3), one. The absolute position can be detected by the head 4.

In the detection device 2 according to the first to third embodiments of the present invention,
The head 4 has one light source 10 and one detection unit 20, and in a first region between two points (P1, P2) separated by a known distance L1, the light from the light source 10 at one point (P1). The positive or minus M (integer of M: 1 or more) next diffracted light is incident on the diffraction grating at the other point (P2), and the first diffracted light of the minus or plus M order is incident. Is obtained, and in the second region between two points (P3 (P2), P4) separated by a known distance L1, the polarization of the light from the light source 10 is incident at one point (P3 (P2)). The positive or negative Mth order diffracted light is incident on the diffraction grating at the other point (P4) to acquire the negative or positive Mth order second diffracted light, and the acquired first diffracted light and the second diffracted light are obtained. The absolute position in the diffraction grating can be detected based on the combined light (interference light) of the diffracted light.

With such a configuration, the absolute position on the diffraction grating can be detected by using the compact head 4 with one light source 10 and one detection unit 20.

Further, in the detection device 2 according to the fourth embodiment of the present invention,
The head 4 has a first detection unit 20A corresponding to the first light source 10A and the first light source 10A, and a second detection unit 20B corresponding to the second light source 10B and the second light source 10B. Plus or minus M obtained by incident light polarization from the first light source 10A at one point (P1) in one region between two points (P1, P4) separated by a known distance (2L1 + 1). Minus or plus Mth-order diffracted light obtained by incident the polarized light of the next diffracted light (an integer of M: 1 or more) and the light from the first light source 10A at the other point (P4) on the diffractive lattice. The first detection unit 20B that receives the combined light (interference light) of the above generates a detection signal, and at one point (P2) in another region between two points (P2, P3) separated by a known distance L2. Plus or minus N (an integer of N: 1 or more) next diffracted light obtained by incident light polarized light from the second light source 10B, and light from the second light source 10B at the other point (P3). The second detection unit 20B, which receives the combined light (interference light) of the minus or plus Nth-order diffracted light obtained by incidenting the polarization of the above into the diffraction lattice, generates a detection signal, and the first detection unit 20A and The absolute position on the diffraction grid can be detected based on the difference between the detection signals by the second detection unit 20B.

With such a configuration, by having the individual light sources 10A and 10B and the detection units 20A and 20B, it is not necessary to use an optical member such as a mirror for incident the diffracted light from the diffraction grating on the diffraction grating again, and the reliability is high. A high detection device 2 can be provided.

Further, the modified example shown in FIG. 9 can be similarly applied not only to the first embodiment shown in FIG. 5 but also to, for example, the second embodiment shown in FIG. Even in that case, in both P-polarized light and S-polarized light, the primary diffracted light is incident on the detection surface 50a from the direction perpendicular to the detection surface 50a, and the -1st diffracted light of the primary diffracted light is detected from the detection surface 50a. It emits in a direction perpendicular to the surface 50a. Therefore, even if the detection surface 50a fluctuates slightly in the vertical direction, the -1st-order diffracted light of the first-order diffracted light is always incident on the detection unit 20. Therefore, even if the clearance of the detection surface 50a fluctuates, it can be absorbed and reliably detected.

Although the embodiments and embodiments of the present invention have been described, the disclosed contents may be changed in the details of the configuration, and the invention in which the embodiments and the combinations and orders of the elements in the embodiments are changed are requested. It can be realized without deviating from the scope and ideas of.

2 Detection device 4 Head 6 Moving mechanism 10 Light source 10A First light source 10B Second light source 20 Detection unit 20A First detection unit 20B Second detection unit 30a to d Mirror 30b1, b2, c1, c2 Mirror 32a to d Reflective wave plates 40, 40a, b Polarized beam splitter (PBS)
50 Scale 50a Detection surface R1 First region R2 Second region

Claims (8)

Light source and
Diffraction light obtained by incident light from the light source on two points on the diffraction grating at a known distance, and two points on the diffraction grating that are at least one point different from the two points at a known distance. A detection unit that receives the combined light (interference light) of the diffracted light obtained by incident light from the light source.
Equipped with one head with
The diffraction gratings differ in the interstitial distance at least in part in two regions between two points separated by the known distance.
A detection device characterized in that an absolute position in the diffraction grating is detected based on the combined wave light (interference light) received by the detection unit.
The detection device according to claim 1, wherein the same detection unit receives a combined light of light having phase information at each diffraction point.
The head has one light source and one detector.
If M is an integer greater than or equal to 1,
In the first region between two points at known distances, the polarized light from the light source is incident at one point and the resulting positive or negative Mth order diffracted light is applied to the grating at the other point. Make it incident and acquire the first diffracted light of minus or plus M order,
In a second region between two points at known distances, the polarized light from the light source is incident at one point and the resulting positive or negative Mth order diffracted light is applied to the grating at the other point. Make it incident and acquire the second diffracted light of minus or plus M order,
The detection device according to claim 1 or 2, wherein the absolute position in the diffraction grating is detected based on the acquired combined light (interference light) of the first diffracted light and the second diffracted light.
The head has a first light source, a first detection unit corresponding to the first light source, a second light source, and a second detection unit corresponding to the second light source.
If M and N are integers of 1 or more,
In one region between two points at known distances, positive or negative M-th order diffracted light obtained by incident polarization of the light from the first light source at one point, and said at the other point. The first detection unit that receives the combined light (interference light) of the minus or plus Mth order diffracted light obtained by incidenting the polarization of the light from the first light source on the diffraction grating generates a detection signal. ,
In the other region between two points at known distances, the positive or negative Nth order diffracted light obtained by incident polarization of the light from the second light source at one point, and said at the other point. The second detection unit that receives the combined light (interference light) of the minus or plus Nth order diffracted light obtained by incidenting the polarization of the light from the second light source on the diffraction grating generates a detection signal. ,
The detection according to any one of claims 1 to 3, wherein the absolute position in the diffraction grating is detected based on the difference between the detection signals by the first detection unit and the second detection unit. apparatus.
The diffraction grating according to claims 1 to 4, wherein the diffraction grating has a lattice pattern in which one absolute position is determined by a difference in the distance between the gratings even if the two regions are located at arbitrary positions on the diffraction grating. The detection device according to any one item.
The detection device according to claim 5, wherein the diffraction grating has a lattice pattern in which the diffraction grating becomes sparse to dense as it progresses from one end to the center and becomes dense to sparse as it progresses from the center to the other end. ..
The phase information of the grating is determined corresponding to the inter-grating distance, the phase information is obtained by the diffracted light at two points separated by a known distance in the two regions, and the phase information obtained by the diffracted light is obtained. The detection device according to any one of claims 1 to 6, wherein the absolute position in the diffraction grating is detected based on the difference of the difference due to the above.
The detection device according to claim 7, wherein the phase information obtained by the lattice is approximated by a cubic equation, and the difference between the differences in the phase information obtained by the diffracted light is approximated by a linear equation.