JP5613893B2 - Table positioning device and positioning method in work device. - Google Patents

Description

  The present invention relates to a table positioning method and a device for a defect repair device, a solution coating device, an exposure device and the like that perform a required work on a workpiece such as an electronic circuit board.

Conventionally, as a table positioning device in this type of working device, a laser length measuring device is arranged at the center on one side of the base supporting the table in the Y-axis direction, and the laser head is fired from the laser head of the laser length measuring device. A laser is irradiated to a target prism provided in the central portion on one side in the X-axis direction of the table, and the position in the Y-axis direction of the table is measured by the laser length measuring device based on the laser reflected therefrom. Is used for positioning the table (for example, see Patent Document 1).
In addition, a laser head of a laser length measuring device is disposed at a corner of the base that supports the table, and a pair of laser interferometers are disposed at an end in the Y-axis direction of the base and spaced apart in the X-axis direction. By irradiating the laser emitted from the laser head onto the reflecting surface of the mirror provided on the table by each laser interferometer, the position in the Y-axis direction of the table is measured by each laser interferometer, and the measured values Is used for positioning the table, and the yaw angle of the table is detected by the difference between the measured values of a pair of laser interferometers, thereby correcting the position of the table. (For example, refer to Patent Document 2).
JP 2004-205441 A JP 2004-349494 A

In general, a laser length measuring device measures the length based on the wavelength of the laser to be used. However, since the wavelength of the laser changes depending on the surrounding environment, the working device provided with the laser length measuring device is temperature-controlled. It is installed and operated in a chamber in which environmental conditions such as atmospheric pressure and humidity are strictly controlled, so that measurement by a laser length measuring instrument can be performed with high accuracy without being affected by the surrounding environment. However, since the working device has a heat source, there is a limit in stabilizing the temperature condition in the chamber uniformly over the entire region. In particular, the larger the chamber is, the more easily the temperature unevenness occurs. In reality, there is a difference in temperature at a certain position of the laser optical axis of the vessel.
In the former of the table positioning device in the working device, when the table performs a yawing motion, a component in the Y-axis direction of the displacement in the X-axis direction of the table due to the yawing motion occurs as an error in the position of the table in the Y-axis direction. There is a problem that the table cannot be accurately positioned at the set position.
Moreover, in the latter of the table positioning apparatus in the said working apparatus, if a pair of laser interferometer is not correctly installed in the symmetrical position of both sides from the center in the X-axis direction of a table, the average value of a measured value of a pair of laser interferometer However, the accurate measurement value in the Y-axis direction at the center in the X-axis direction of the table is not obtained, and accurate positioning in the Y-axis direction of the table cannot be performed even if the position is corrected based on the yawing angle. Further, as described above, when there is a difference in temperature at the position of the laser optical axis of the laser length measuring device, the measurement error has a large influence on the measured value with the larger temperature change on the left and right in the pair of laser interferometers. The average value of the measured values and the yawing angle fluctuate, and there is a problem that the positioning of the table in the Y-axis direction cannot be repeatedly performed with high accuracy.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a table positioning method in an operation apparatus and a device thereof that can repeatedly reproduce positioning of a table with high accuracy.

The table positioning device in the working device according to the present invention includes a fixed base, a table that supports a workpiece and is movable in one direction with respect to the base, and a column that is erected on the base. A beam fixedly provided above the table and provided in a direction orthogonal to the moving direction of the table, a slider provided movably along the beam, and a working head attached to the slider And a first driving means for moving the table in the one direction, a second driving means for moving the slider along the beam, and a position of the table fixed to the base. For measuring the workpiece on the table based on the measurement result by the laser length measuring device. The table positioning device in the working device for positioning at a predetermined position with respect to the work head, wherein the laser length measuring device has a center position in a direction perpendicular to the moving direction of the table, and a distance between both sides of the center position. And a laser interferometer that is disposed at each of the two positions and measures the position of the table, and the table reflects the laser light emitted from each laser interferometer in the irradiation direction. Each of the table and the target prism is moved in a direction in which laser light is emitted from the laser interferometer, and the control device is measured by laser interferometers arranged on both sides of the center position. Calculate the yaw angle of the table based on the measured value, and arrange the laser interferometer at the center position Thus the position of the measuring tables, corrected based on the direction of the setting position orthogonal and the yawing angle in the moving direction of the table, this correction to the obtained position, the set position in the direction of movement of the table It is characterized by operating the first driving means so.

Further, the table positioning method in the working device according to the present invention is a table positioning method by the table positioning device according to claim 1, wherein a space is provided on both sides of the center position in the direction perpendicular to the moving direction of the table. The position of the table is measured by the laser interferometer of the laser length measuring device disposed at two positions, the yawing angle of the table is calculated based on the measured value, and the laser interferometer disposed at the center position Is corrected based on the set position in the direction perpendicular to the moving direction of the table and the yawing angle, and the position obtained by this correction is the set position in the moving direction of the table. is characterized in that way becomes.

In the table positioning apparatus and method in the working apparatus, when the work is moved and the workpiece held on the table is positioned at a predetermined position with respect to the working apparatus, the table is centered in a direction perpendicular to the moving direction of the table. The table moving position measured by the arranged laser interferometer is used as a reference position, and the yawing angle of the table is obtained by the control device from the position in the moving direction of the table measured by the laser interferometers on both sides. The reference position in the moving direction of the table is always corrected based on the corner, and the table is positioned by the driving means based on the corrected reference position. Thereby, the positioning control in the moving direction of the table is realized by suppressing the influence of the yawing motion of the table and improving the repeatability.

  According to the table positioning method and the apparatus thereof in the working device according to the present invention, the moving position of the table measured by the laser interferometer arranged at the center in the direction perpendicular to the moving direction of the table is used as a reference position, The reference position can always be corrected based on the yawing angle of the table obtained from the measured values of the laser interferometers arranged on both sides of the laser interferometer, and the table can be positioned based on the corrected reference position. Therefore, even if the measurement environment by the laser interferometer has temperature unevenness, the influence of the yawing motion of the table can be suppressed and the positioning in the moving direction of the table can be repeatedly reproduced with high accuracy.

Hereinafter, a table positioning device in a working device according to an embodiment of the present invention will be described with reference to the accompanying drawings.
In FIG. 1, reference numeral 1 denotes a work apparatus provided with a table positioning device 2 according to an embodiment of the present invention. This working device 1 is provided along a base 3 installed on the floor and a pair of Y-axis rails (guide rails) 3a and 3a provided in parallel on the top surface of the base 3 in the Y-axis direction y. A table 4 that reciprocates in the Y-axis direction y, and a pair of support columns 5, 5 erected on both ends of the base 3 in the Y-axis direction y (both ends in the X-axis direction x). An X-axis beam 6 fixed to the upper ends of the columns 5 and 5 and directed in the X-axis direction x and an X-axis rail (guide rail) (not shown) provided on the X-axis beam 6 are supported by the X-axis direction x. And an operation head 8 attached to the front side (right side in FIGS. 1 and 2) of the X-axis slider 7.

  The table 4 is fixed to a frame member 4a assembled in a rectangular shape in plan view (FIG. 1) and an upper portion of the frame member 4a, and an electronic circuit board or the like (hereinafter referred to as “work”) W is placed on the upper surface. A rectangular glass plate 4b and an illuminator (not shown) that is disposed below the frame member 4a and irradiates the workpiece W are provided along the Y-axis direction y at the center of the base 3 in the X-axis direction. The Y-axis linear motor (Y-axis drive means) 9 is composed of a Y-axis linear motor fixing portion 9a and a Y-axis linear motor movable portion 9b fixed to the lower surface of the table 4. It is designed to be positioned.

  The X-axis slider 7 is fixed to the support columns 5 and 5 and fixed to an X-axis linear motor arranged in parallel to the X-axis beam 6 on the rear side (left side in FIGS. 1 and 2) of the X-axis beam 6. It is moved and positioned in the X-axis direction x by an X-axis linear motor (X-axis drive means) 10 comprising a portion 10a and an X-axis linear motor movable portion 10b fixed to the X-axis slider 7. . A Z-axis linear motor (Z-axis drive means) 8z that moves and positions the work head 8 in the Z-axis direction z with respect to the X-axis slider 7 is provided between the X-axis slider 7 and the work head 8. ing.

A Y-axis linear encoder 4y (see FIG. 3) is provided between the base 3 and the table 4, between the X-axis beam 6 and the X-axis slider 7, and between the X-axis slider 7 and the work head 8, respectively. 2), an X-axis linear encoder and a Z-axis linear encoder (both not shown in FIGS. 1 and 2) are provided, the position of the table 4 in the Y-axis direction y, the X-axis direction x and Z of the work head 8 Positions in the axial direction z are detected, respectively, and their positioning is performed by feedback control.
The X-axis driving means 10, Y-axis driving means 9 and Z-axis driving means 8z are changed to linear motion by a screw mechanism formed by screwing a ball nut onto a ball screw shaft instead of a linear motor. It may be of a driving type. In that case, a rotary encoder attached to the servo motor is used instead of the linear encoder.

  The working head 8 has a microscope with a CCD camera and includes a measuring head 8a for measuring the position, shape, dimensions, etc. of various defective portions generated on the workpiece W, and the defect is repaired in order to repair the defective portions. A processing head such as a laser processing head that performs precise processing on the part, a solution coating apparatus that applies a repair solution or the like to a portion processed by the processing head, an exposure head that exposes the surface of a workpiece applied by the solution coating apparatus, etc. One or more of them.

  Next, the table positioning device 2 in the working device according to the present invention will be described. As shown in FIGS. 1 to 3, the table positioning device 2 includes a laser length measuring device 11 used for measuring the position of the table 4 and the X-axis slider 7 on the base 3 of the working device 1. . The laser length measuring device 11 is supported by a mounting plate 12 fixed at the center in the X-axis direction x on the rear side of the base 3 (one end side in the Y-axis direction y, left side in FIGS. 1 and 2). The laser head 13 is supported by the mounting plate 12 and a part of the length measuring laser L irradiated from the laser head 13 is moved straight in the Y-axis direction y, and the remaining part is horizontally separated on both sides in the X-axis direction x. Supported by a pair of half mirrors 14 and 14 and a pair of mounting plates 12a and 12b fixed to the base 3, a predetermined distance from the half mirrors 14 and 14 to both sides in the X-axis direction x (equal distance to both sides). However, the length measuring laser L, which is arranged at a position spaced apart from each other and separated by the half mirrors 14 and 14, is placed on the front side of the base 3 (the other end side in the Y-axis direction y, FIG. Half mirror 14a irradiating toward the right side in FIG. And a fine reflecting mirror 14b.

  Further, the laser length measuring device 11 is supported by the mounting plate 12, and a central Y-axis laser interferometer (laser interferometer) 15 disposed opposite to the half mirror 14 in the Y-axis direction y, A Y-axis laser interferometer (laser interferometer) on the right side (upper side in FIGS. 1 and 3) supported by the mounting plates 12a and 12b and disposed opposite to the half mirror 14a and the reflection mirror 14b in the Y-axis direction y. ) 15a and the Y-axis laser interferometer (laser interferometer) 15b on the left side (lower side in FIGS. 1 and 3) and one end of the table 4 in the Y-axis direction y (the left end in FIGS. 1 and 2) The center, right, and left Y-axis target prisms 16, 16a, and 16b are attached to the center, right, and left Y-axis laser interferometers 15, 15a, and 15b so as to face each other in the Y-axis direction y. I have.

  The Y-axis laser interferometers 15, 15a, 15b all have the same configuration, and are irradiated in the Y-axis direction y from the half mirrors 14, 14a and the reflection mirror 14b as shown in FIG. A beam splitter 17 for separating the length measuring laser L into a Y-axis direction y directed to the Y-axis target prisms 16, 16 a, 16 b and an X-axis direction x perpendicular thereto, and a measurement separated from the beam splitter 17. A reference prism 18 that reflects the long laser L as a reference light toward the beam splitter 17, and a photodetector 19 that detects the frequency of the interference light between the reflected light from the Y-axis target prisms 16, 16 a and 16 b and the reference light. It has.

  Further, the laser length measuring device 11 is supported by a mounting plate 12c fixed to a corner (an upper left corner in FIG. 1) of the base 3, and is opposed to the half mirror 14a. Fixed to the upper part of the reflection mirror 14c that irradiates the other end side in the Y-axis direction y with the length measuring laser L separated by 14a and linearly moved in the X-axis direction x, and the one column 5 (upper in FIG. 1). A reflection mirror 14d that is supported by the mounting plate 12d and reflects the length measuring laser L from the reflection mirror 14c toward the X-axis slider 7 along the X-axis direction x, and the reflection mirror 14d in the X-axis direction. An X-axis laser interferometer (laser interferometer) 15c disposed opposite to x and supported on the front side (right side in FIG. 1) of the X-axis slider 7 and in the X-axis direction x on the X-axis laser interferometer 15c X-axis target provided opposite And the prism 16c is provided. The X-axis laser interferometer 15c has the same configuration as each of the Y-axis laser interferometers 15, 15a, 15b.

  The laser head 13 and each photo detector 19 detect the positions of the table 4 at the center and both sides in the X-axis direction x based on the reference signal from the laser head 13 and the output signal of each photo detector 19. A length measurement calculation unit 20 is connected. Then, the Y-axis linear motor 9, the X-axis linear motor 10, the length measurement calculation unit 20 of the laser length measuring device 11, the linear encoder 4 y, and the like are based on the output of the length measurement calculation unit 20. A controller (control device) 21 for controlling the operation of the above is electrically connected. The laser length measuring device 11 itself, which includes the laser head 13, the Y-axis laser interferometers 15, 15a, 15b, the Y-axis target prisms 16, 16a, 16b, the length measuring unit 20 and the like, is well known in the art. is there.

  The controller 21 inputs position information of the center in the X-axis direction x of the table 4 obtained by the length measuring unit 20 based on the outputs from the Y-axis laser interferometers 15, 15a, 15b and both sides thereof. A calculation control unit 21a for calculating a yaw angle of the table 4 and outputting a position control signal corresponding to the center position in the X-axis direction x of the table 4 corrected based on the yawing angle; and the position control signal And a motor driver 21c that is input via the interface 21b and operates the Y-axis linear motor 9. The motor driver 21 compares the position control signal with the position signal from the Y-axis linear encoder 4y that has detected the position of the table 4 that is driven by the Y-axis linear motor 9 and moves, and the table 4 is always in the control command position. The Y-axis linear motor 9 is feedback-controlled so as to be moved and positioned at the same time.

Next, the table positioning method will be described together with the operation of the table positioning device 2 in the working device 1 configured as described above.
For example, in the case of performing fine processing for repairing a predetermined part such as a defective portion generated in the workpiece W, the table 4 is placed on the front side of the base 3 (right side in FIG. 1) as shown by a chain line in FIG. In the state where the workpiece W is held on the glass plate 4b, the laser-side elongated device 11 is operated via the controller 21, and the X-axis linear motor 10 and the Y-axis linear motor 9 are operated. When operated, the X-axis slider 7 and the table 4 are moved relative to each other in the X-axis direction x and the Y-axis direction y, and the work head 8 is moved and positioned above a predetermined portion of the workpiece W. The

  In the controller 21, the table 4 corresponding to a predetermined part of the workpiece W and the coordinates (X, Y) of the movement position Pxy of the X-axis slider 7 are stored in advance in the storage unit of the arithmetic control unit 21a as a set position. Therefore, the X and Y axis linear motors 10 and 9 include the X axis encoder 7 (not shown) and the X axis slider 7 detected by the Y axis linear encoder 4y and the X and Y axis directions x, Feedback control is performed by the motor driver 21c based on the position control signal at y, the X-axis slider 7 and the table 4 are driven, and the working head 8 is accurately positioned above a predetermined portion of the workpiece W.

  At that time, in the laser length measuring device 11, the laser L oscillated by the laser head 13 and divided into three by the half mirrors 14 and 14 and the reflection mirrors 14a and 14b is respectively converted into the Y-axis laser interferometers 15 and 15 respectively. The laser L irradiated to and reflected from the Y-axis target prisms 16, 16a, 16b on the center, right side, and left side attached to one end of the table 4 through 15a, 15b is reflected by the Y-axis laser interferometers 15, 15a, The photo detectors 19 b detect the output of the photo detectors 19 b and output the photo detectors 19 to the length measurement calculation unit 20. Therefore, the length measurement calculation unit 20 detects the positions P, Pa, and Pb in the Y-axis direction y corresponding to the Y-axis target prisms 16, 16a, and 16b at the center, right side, and left side of the table 4, and the positions are detected. Information (pulse signal) is input to the arithmetic control unit 21 a of the controller 21.

For example, as shown by a broken line in FIG. 3, the table 4 is tilted with respect to the Y-axis direction y by the yawing motion, and the right-side Y-axis target prism 16a is moved in the traveling direction of the table 4 (leftward in FIG. When the state precedes (downward in FIG. 4), the positions P, Pa, and Pb on the center and both sides of the table 4 in the Y-axis direction y are related positions as shown in FIG. The unit 21a performs calculation according to the following Y coordinate calculation formulas (1) and (2) based on the position information regarding the positions P, Pa, and Pb input from the length measurement calculation unit 20, and the y coordinate at the set position Pxy. (Positioning position of the table 4 in the Y-axis direction y) Y is a position P in the center of the table 4 as a reference position, and its y coordinate Y1 is taken into account the yawing angle of the table 4 Obtained as Tadashisa the y coordinate values.
Y = Y1 + Ya−Y2 (1)
Y2 = (Ya + Yb) · X2 / X1 (2)
Where X1 is the distance in the X-axis direction between the positions Pa and Pb of the target prisms 16a and 16b on both sides, and X2 is the X-axis direction from the position Pa of the right Y-axis target prism 16a to the x coordinate X of the set position Pxy. Distance, Ya is the distance in the Y-axis direction y from the central position P to the right Y-axis target prism 16a, Yb is the distance in the Y-axis direction y from the central position P to the left Y-axis target prism 16b, Y2 is a distance in the Y-axis direction y from the position Pa of the right Y-axis target prism 16a to the y-coordinate Y of the set position Pxy.

Thus, the y-coordinate Y at the set position Pxy obtained by calculating according to the Y-coordinate calculation formulas (1) and (2) in the calculation control unit 21 instructs the positioning position of the table 4 in the Y-axis direction y. As described above, the position control signal is input to the motor driver 21c via the interface 21b and the Y-axis linear motor 9 is driven by feedback control, so that the table 4 is affected by the yawing motion. Instead, it is always accurately positioned at a predetermined position in the Y-axis direction y.
Then, the position P at the center of the table 4 is uniquely measured by one Y-axis laser interferometer 15, and the measured value is a chamber in which the working device 1 (laser interferometers 15, 15a, 15b) is installed. Even if there is temperature unevenness in the table 4, it can be obtained as a reference value for position control in the Y-axis direction of the table 4 regardless of the measurement values by the other Y-axis laser interferometers 15a and 15b. By performing yawing correction based on the measured values of the Y-axis laser interferometers 15b and 15a, even if the temperature change in the chamber (measurement environment by the laser interferometer) is ± 0.1 ° C., for example, the influence thereof And the positioning of the table 4 in the Y-axis direction is repeated repeatedly with high accuracy.

  As described above, the table positioning method in the working device according to the embodiment moves the table 4 supporting the workpiece W, measures the moving position with the laser length measuring instrument 11, and based on the measurement result. A table positioning method in a working apparatus for positioning a work W on the table 4 at a predetermined position with respect to a work head 8, wherein a space is provided on both sides of a center position P in a direction perpendicular to the moving direction of the table 4. The position of the table 4 is measured by the Y-axis laser interferometers 15a and 15b of the laser length measuring device 11 arranged at the two positions Pa and Pb, and the yawing angle of the table 4 is calculated based on the measured values. The position of the table 4 measured by the laser interferometer 15 arranged at the center position P is set to the yawing angle. It corrected Zui and has the structure for positioning the table 4 on the correction to the determined position.

  The table positioning device 2 in the working device according to the embodiment moves the table 4 supporting the workpiece W by operating the Y-axis linear motor 9 with the controller 20, and the moving position is measured by the laser length measuring device 11. A table positioning device in a working device for measuring and positioning the work W on the table 4 with respect to the working head 8 at a predetermined position in the Y-axis direction y based on the measurement result, the laser length measuring device 11 Are arranged at a center position P in the X-axis direction x perpendicular to the Y-axis direction y of the table 4 and at two positions Pa and Pb spaced on both sides of the center position P, respectively. Measuring the center, right side, and left side Y-axis laser interferometers 15, 15a, 15b. The yaw angle of the table 4 is calculated based on the measurement values measured by the Y-axis laser interferometers 15a and 15b disposed on the side, and the table measured by the Y-axis laser interferometer 15 disposed at the center position. 4 is corrected based on the yawing angle, and the Y-axis linear motor 9 is operated so that the table 4 is positioned at the position obtained by the correction.

  Therefore, according to the table positioning method in the working device according to the embodiment and the table positioning device 2 in the working device according to the embodiment, the Y-axis laser disposed in the center in the direction perpendicular to the moving direction of the table 4 Using the movement position P of the table 4 measured by the interferometer 15 as a reference position, the table 4 obtained from the measured values of the Y-axis laser interferometers 15a and 15b arranged on both sides of the central Y-axis laser interferometer 15 is used. Since the reference position is always corrected based on the yawing angle and the table 4 can be positioned based on the corrected reference position, even if the measurement environment by the laser interferometer has temperature unevenness, Positioning in the moving direction of the table 4 is repeatedly reproduced with high accuracy while suppressing the influence of yawing motion. Rukoto can.

  In the table positioning device 2 in the working device according to the embodiment, the laser length measuring device 11 has one for the Y-axis laser interferometers 15, 15a, 15b at the center, the right side, and the left side. The length measuring laser L from the laser head 13 is irradiated in three divided parts via the half mirrors 14 and 14 and the reflecting mirrors 14a and 14b. However, the present invention is not limited to this. You may make it irradiate with the laser head 13 provided separately with respect to the axial laser interferometer 15, 15a, 15b.

It is a top view which shows the working apparatus provided with the table positioning apparatus which concerns on one embodiment of this invention. It is the side view which similarly showed a part in cross section. It is a control system diagram which shows the table positioning device in the working device which concerns on one embodiment of this invention. It is an operation explanatory view of a table positioning device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Work apparatus 2 Table positioning apparatus 3 Base 4 Table 6 X-axis beam 7 X-axis slider 8 Work head 9 Y-axis linear motor (Y-axis drive means)
10 X-axis linear motor (X-axis drive means)
11 Laser length measuring device 13 Laser head 14, 14a Half mirror 14b, 14c, 14d Reflection mirror 15, 15a, 15b Y-axis laser interferometer (laser interferometer)
16, 16a, 16b Y-axis target prism 16c X-axis target prism 17 Beam splitter 18 Reference prism 19 Photo detector 20 Measurement unit 21 Controller (control device)
21a Operation control unit W Workpiece

Claims (2)

A fixed base, a table that supports a workpiece and is movable in one direction with respect to the base, and is fixed to a column that is erected on the base and is provided above the table. A beam provided in a direction orthogonal to the moving direction of the table, a slider provided movably along the beam, a working head attached to the slider, and a first moving the table in the one direction. 1 driving means, second driving means for moving the slider along the beam, a laser length measuring device fixed to the base for measuring the position of the table, the first, And a control device that operates the driving means of the two, and a work device that positions a work on the table at a predetermined position with respect to the work head based on a measurement result by the laser length measuring device. A positioning device of the table that,
The laser length measuring device is arranged at a center position in a direction perpendicular to the moving direction of the table and two positions spaced on both sides of the center position to measure the position of the table. Equipped with a meter,
The table is provided with a target prism that reflects the laser beam emitted from each laser interferometer in the irradiation direction, and the moving direction of the table and the target prism is the direction in which the laser beam is emitted from the laser interferometer. And
The control device calculates a yawing angle of the table based on the measurement values measured by the laser interferometers arranged on both sides of the center position, and the table measured by the laser interferometer arranged at the center position. Is corrected based on the set position in the direction orthogonal to the moving direction of the table and the yawing angle, and the position obtained by this correction becomes the set position in the moving direction of the table . A table positioning device in a working device, wherein one driving means is operated. A table positioning method by the table positioning device according to claim 1,
The position of the table is measured by the laser interferometer of the laser length measuring device arranged at two positions spaced on both sides of the center position in the direction perpendicular to the moving direction of the table, and the table is based on the measured value. along with calculating the yaw angle, the position of the measuring tables by arranged laser interferometer to the center position is corrected on the basis of said yawing angle and direction of the set position perpendicular to the moving direction of said table, A table positioning method in a working apparatus , wherein the position obtained by the correction is a set position in the moving direction of the table.

Images