JPH0643973B2 - Automatic optical axis adjusting device for goniometer of X-ray diffractometer - Google Patents

Description

The present invention relates to an automatic optical axis adjusting device for automatically adjusting the optical axis of a goniometer of an X-ray diffractometer.

[Prior Art] The optical axis adjustment of a goniometer of an X-ray diffractometer has several steps described below.

(a) When the rotation angle (2θ) of the detector arm is set to zero, the divergence slit, the rotation axis of the sample table (hereinafter referred to as the sample axis), and the light-receiving slit on the detector arm are aligned. Adjustments to come. This adjustment has already been adjusted at the manufacturing stage of the goniometer.

(b) The X-ray focus should be on the optical axis of the goniometer.
Adjustment that determines the relative positional relationship between the line focus and the goniometer. This adjustment is done by rotating the goniometer base slightly.
The output of the X-ray detector is adjusted to be maximum.

(c) Confirmation of 2θ = zero. This confirmation is performed as follows. The detector arm is slightly rotated in the vicinity of 2θ = zero to obtain the peak profile, and the midpoint of the half width of the detected peak is set as the zero peak position. Next, it is confirmed that the deviation between the position of the zero peak and the position of the zero mark on the detector arm base is settled within a predetermined angle range.
If the angle is not within the predetermined angle range, the adjustment from (b) above will be performed again.

(d) Adjustment of the rotation angle (θ) of the sample table = zero. In this adjustment, the sample stage is finely rotated in the vicinity of θ = zero so that the output of the X-ray detector is maximized. At that time, the optical axis adjusting jig is attached to the sample table. The reference plane of this jig is in the plane including the sample axis, and the reference plane becomes parallel to the incident X-ray near θ = 0.

Among the above optical axis adjustments, the present invention is intended to automate the optical axis adjustments of (b) (c) (d). Conventionally, in the adjustment of (b), the goniometer base is manually rotated minutely by using an adjusting screw or the like. Also, in the adjustment of (c) (d), 2
Although the θ rotation motor and the θ rotation motor are used to rotate the X-ray detector arm base and the sample base by motor drive,
An adjusting operator gave a rotation instruction to these motors each time.

[Problems to be Solved by the Invention] The above-described conventional optical axis adjustment has the following problems.

The fine rotation adjustment of the goniometer base must be done by hand, which is very troublesome. The confirmation of 2θ = zero and the adjustment of θ = zero are performed only by rotating the motor, but it is still the task of the adjusting operator to give a rotation instruction to the motor while confirming the X-ray intensity. Therefore, the X-ray diffractometer is inevitably troublesome during the adjustment of the optical axis.

Therefore, there is an increasing demand for automating such optical axis adjustment, and an object of the present invention is to provide an automatic optical axis adjusting apparatus for a goniometer of an X-ray diffraction apparatus, which can satisfy such requirements. .

[Means for Solving Problems] First, a mechanism for automatically making a minute rotation of the goniometer base is required. Furthermore, it is necessary to independently rotate the three motors (base rotation motor, 2θ rotation motor, θ rotation motor) according to a predetermined program and according to the detected X-ray intensity, and a control device therefor. Is also necessary. Therefore, an automatic optical axis adjusting device for a goniometer of an X-ray diffractometer according to the present invention includes a goniometer base rotatable with respect to an X-ray source and an X-ray detector rotatable with respect to the goniometer base. In an X-ray diffractometer having an X-ray detector arm base to which is attached and a sample base rotatable with respect to the goniometer base, (a) a base rotary motor and (b) a 2θ rotary motor (C) a θ rotation motor, (d) a first transmission mechanism that transmits the rotation of the base rotation motor to the goniometer base, (e) the rotation of the 2θ rotation motor the X-ray detector arm base Based on peak information of the output of the X-ray detector, (f) a third transmission mechanism that transmits the rotation of the θ rotation motor to the sample stage,
A control device that independently controls the base rotation motor, the 2θ rotation motor, and the θ rotation motor.

As described above, the goniometer base, the X-ray detector arm base, and the sample base can be separately driven by motors, whereby the optical axis adjustment can be automated.

In order to adjust the optical axis, all of the above-mentioned three driven parts must be minutely rotated with high precision, and therefore the three motors for that purpose must be motors that satisfy such requirements. Preferably, a pulse motor can be used as these motors.

Although various mechanisms such as a worm / worm wheel transmission mechanism can be used as the first transmission mechanism, it is optimal to use an eccentric cam mechanism as described in the following embodiments. Although various transmission mechanisms can be adopted for the second transmission mechanism and the third transmission mechanism, it is convenient to use the worm / worm wheel transmission mechanism as it is, like the conventional goniometer.

A microcomputer is optimally used to control the above-mentioned three motors according to a predetermined program.

[Embodiment] An embodiment of the present invention will be described below in the following order.

I. Overall configuration of X-ray diffractometer b. Control system of automatic optical axis adjuster c. Rotation drive mechanism of goniometer base D. Optical axis adjustment jig e. Operation procedure of automatic optical axis adjustment device a. Overall Structure of X-Ray Diffraction Apparatus FIG. 1 is a schematic plan view of an X-ray diffraction apparatus equipped with an embodiment of the present invention, and FIG. 2 is a front view showing a part of the section. An X-ray tube 14 having a target 12 is fixed to the frame 10, and X-rays are generated from an X-ray focus 16 on the target 12. This X-ray tube 14 is the X of the X-ray diffractometer.
It constitutes the radiation source. The X-ray tube 14 has an X-ray shutter 1
5 is attached.

A plate 18 is fixed to the frame 10, and a rotatable goniometer base 20 is mounted on the plate 18. On the goniometer base 20, further, a sample base 22 and a detector arm base 24, which are rotatable relative to the base 20, are provided.
Is listed. The detector arm 2 is attached to the detector arm base 24.
6 is fixed, and the X-ray detector 28 is fixed to the detector arm 26.

The divergence slit 30 is fixed to the goniometer base 20,
The anti-scattering slit 32 and the light receiving slit 34 are fixed to the detector arm 26. Then, when the rotation angle 2θ of the detector arm 26 is set to zero, the optical axis is adjusted so that the divergence slit 30, the sample shaft 36, the scattering prevention slit 32, and the light receiving slit 34 are on the straight line 38. The sample shaft 36 is the center of rotation of the sample table 22 and also coincides with the center of rotation of the detector arm table 24.

The sample table 22 is rotationally driven by a pulse motor (θ rotation motor) 40. That is, the worm wheel 42 is fixed to the sample table 22, and the worm 44 that meshes with the worm wheel 42 is fixed to the rotation shaft of the pulse motor 40. The detector arm base 24 is also rotationally driven by the pulse motor 50 via the worm wheel 46 and the worm 48. Sample stand 22 and detector arm stand 24
Can be interlocked at a rotation ratio of 1: 2, and can also be independently rotated. Single rotation is used for automatic optical axis adjustment. The pulse motors 40 and 50 are five-phase pulse motors.

The mechanism for minutely rotating the goniometer base 20 will be described in detail in the section “C. Rotational drive mechanism of the goniometer base” below.

B. Control System of Automatic Optical Axis Adjustment Device FIG. 3 shows a control system of the automatic optical axis adjustment device. A high voltage power supply 52 is connected to the X-ray detector 28, and the X-ray detection signal is input to a wave height analyzer 54 via an amplifier. The signals in the predetermined intensity range are counted by the counter 56, and the count value is input to the input interface 60 of the control device 58. A command for starting automatic optical axis adjustment is input from the keyboard 62. The keyboard 62 is used not only for automatic optical axis adjustment but also for inputting various data and work instructions when measuring a sample.

The control device 58 includes a CPU 64, a ROM 66, a RAM 6
8 includes an input interface 60 and an output interface 70. The motor drivers 72, 74, 76 for the pulse motors are also included in the control device 58. A program for automatic optical axis adjustment is stored in the ROM 66. A command from the CPU 64 is sent to the motor drivers 72, 7 via the output interface 70.
4, 76, CRT display 78, X-ray shutter electromagnetic solenoid 80. Motor driver 72,7
The output pulse signals from 4, 76 are three pulse motors, that is, the base rotary motor 82, the 2θ rotary motor 5
0 and θ rotation motors 40 respectively.

C. Rotational Drive Mechanism of Goniometer Base In FIG. 1, a rough adjustment block 84 is provided on the plate 18.
Is listed. This rough adjustment block 84 is used for the plate 1
8 relative to each other, and a pair of coarse adjustment screws 86, 88
Can be moved to the left and right in FIG.
That is, if the left coarse adjustment screw 86 is loosened and the right coarse adjustment screw 88 is tightened, the coarse adjustment block 84 moves to the left, and if the reverse operation is performed, the coarse adjustment block 84 moves to the right. The coarse adjustment block 84 also includes the coarse adjustment block 8
Locking screws 90 and 92 for fixing 4 are attached.

A pulse motor (base rotation motor) 82 is fixed to the coarse adjustment block 84. The pulse motor 82 is a five-phase pulse motor, which can rotate by 0.72 ° per pulse, and makes one rotation in 500 pulses. As shown enlarged in FIG. 4, an eccentric cam 96 is fixed to the output shaft 94 of the pulse motor 82. The rough adjustment block 84 is not shown in FIG. The eccentric cam 96 has a circular contour 98, and the distance between the center of the circular contour 98 and the center of rotation is ε.
Only eccentric. The contour is circular because it is easy to perform accurate machining. Further, the shaft hole for fixing the output shaft 94 to the eccentric cam 96 is also easy to machine.

The cam follower 100 is fixed to the goniometer base 20. A groove 102 is formed in the cam follower 100, and the opposing wall surfaces 104 and 106 of the groove 102 come into contact with the circular contour 98 of the eccentric cam 96. Such a groove 102 can also be machined with high precision. The width of the groove 102 is almost the same as the diameter of the circular contour 98 of the eccentric cam 96, but strictly speaking,
It is slightly wider than the diameter of the circular contour 98. The circular contour 98 of the eccentric cam 96 is also the groove 10 of the cam follower 100.
Since No. 2 can also be machined with high precision, the gap between them can be almost eliminated.

In this embodiment, the distance L (see FIG. 1) from the center of the output shaft of the pulse motor 82 to the sample shaft 36 is set to 220 mm. Further, the eccentricity amount ε of the eccentric cam 96 (fourth
(See the figure) is set to 0.8 mm.

Next, the operation of this drive mechanism will be described. In FIG. 1, first, as a preliminary adjustment, the coarse adjustment block 84 is adjusted. Manually operate the coarse adjustment screws 86, 88,
The rough adjustment block 84 is slightly moved to the left and right to determine the rough rotation position of the goniometer base 20. By moving the rough adjustment block 84, the goniometer base 20 can be rotated via the pulse motor 82, the eccentric cam 96, and the cam follower 100. Such a rough adjustment can be easily performed with reference to the X-ray intensity of the detector 28. After rough adjustment, lock screw 9
Tighten 0 and 92 to attach the coarse adjustment block 84 to the plate 1.
Fix at 8. It should be noted that such a rough adjustment does not need to be carried out frequently, and in the normal optical axis adjustment, only the automatic optical axis adjustment work described later is sufficient.

Next, the relationship between the rotation angle α of the pulse motor 82 and the rotation angle β of the goniometer base 20 will be described with reference to FIG.

Now, when the eccentric cam 96 is in the state shown by the solid line in FIG. 5, the reference position is set, and the rotation angle in this state is set to zero. When the pulse motor rotates clockwise by the angle α, the eccentric cam 96 also rotates by the same angle. At this time,
The cam follower 100 moves to the left by a distance d, and the moving distance is d = ε · sin α (1). Since the cam follower 100 is fixed to the goniometer base, the goniometer base 20 rotates by the angle β, and the rotation angle is approximately β = sin ⁻¹ (d / L) (2).

Since the pulse motor rotates by 0.72 ° (Δα) per pulse, the rotation angle (Δβ) of the goniometer base per pulse can be obtained from the above equations (1) and (2). However, even with a constant Δα, the change amount Δd of the distance d changes depending on the position of the eccentric cam. For example, Δd is large in the vicinity of α = 0 °, and Δd is small in the vicinity of α = 90 °. Now consider the average value of Δd Δd _av . 250 to rotate the pulse motor half a turn
Pulse is required, and the cam follower then has 2ε = 1.
Move 6 mm. Therefore, the cam follower moves on average by Δd _av = 1.6 / 250 = 0.0064 mm every time one pulse is supplied to the pulse motor. The rotation angle of the goniometer base at this time is L = 22 in the above equation (2).
If 0 mm, Δβ _av = 0.00167 °.

Table 1 below shows the numerical values related to the rotation adjustment of the goniometer, using the average rotation angle Δβ _av of the goniometer base per pulse thus obtained.

In this table, the acceptable angle difference means an angle range within which the optical axis adjustment is considered to have been performed correctly regardless of the position of the goniometer base. In this drive mechanism, the minimum operation of the pulse motor is ⅙ of the acceptable angle difference, and it can be seen that the drive motor has sufficient adjustment accuracy. The peak half width is the standard half width of the zero peak that appears when performing rotation adjustment.

FIG. 6 illustrates the operation of this drive mechanism.
FIG. 6 (a) shows the movement amount d of the cam follower as a function of the rotation angle α of the pulse motor (the rotation angle of the eccentric cam is the same). It is a function.

FIG. 6 (b) is a time chart of the datum switch. The datum switch plays a role of defining a reference position for rotation of the pulse motor, and is turned on only once at a specific position during one rotation of the pulse motor. The ON position is defined as the pulse motor rotation angle α = zero. That is, every time the pulse motor makes one rotation, the rotation angle of the pulse motor returns to zero. Actually, the rotation angle of the pulse motor is measured by counting the number of pulses supplied to the pulse motor with the control device, and the datum switch is turned on.
Then, this count is reset to zero.

D. Optical Axis Adjustment Jig FIGS. 7a and 7b show two states of the optical axis adjustment jig used in the automatic optical axis adjustment work. In FIG. 7a, this jig 108 is attached to the sample table.
On its one side, there are two elongated reference planes 11 with a width of 2 mm.
0 and 112 are formed, and in the meantime, 114 is the reference plane 11.
It is 0.5 mm lower than 0 and 112. To attach the jig 108 to the sample table, the reference plane 11
The lower half of 0, 112 may be brought into contact with the reference surface of the sample table, and at this time, the two reference planes 110, 112 are positioned within the plane including the sample axis.

Through holes 116 are formed in the jig 108. The through hole 116 penetrates in a direction perpendicular to the reference planes 110 and 112. The cross-sectional dimension of the through hole 116 perpendicular to the through direction is 12 mm × 20 mm. Through hole 11
The cross-sectional size of 6 is X-ray 11 coming from the divergence slit.
It is large enough to pass 8 without any obstacles. Figure 7a shows the position adjustment of the goniometer base and 2θ.
= Shows the state of the jig 108 when adjusting zero.
FIG. 7b shows the state of the jig 108 when adjusting θ = 0.

E. Operation Procedure of Automatic Optical Axis Adjustment Device The operation of the automatic optical axis adjustment device will be described below with reference to the flowcharts of FIGS. 8 to 12.

FIG. 8 shows the procedure before and after the automatic optical axis adjustment work. Before starting the automatic optical axis adjustment work, first, attach the optical axis adjustment parts to the slit system and the sample table (step 12).
0). That is, a divergence slit with an opening width of 0.05 mm is attached to the divergence slit box, an aluminum absorption plate is attached to the scattering prevention slit box, and a light receiving slit with an opening width of 0.15 mm is attached to the light receiving slit box. . The above-mentioned optical axis adjusting jig 108 is attached to the sample table. Up to this point, the operator manually does this. Next, when an instruction for automatic optical axis adjustment is given from the keyboard, the automatic optical axis adjustment work is carried out according to a predetermined program (step 122). When the automatic optical axis adjustment work is completed, the worker attaches the diffraction measurement parts to the slit system and the sample stage (step 124). That is,
The divergence slit box has a divergence slit with an opening angle of 1 °, and the scattering prevention slit box has an opening angle of 1 °.
A scattering prevention slit of ° is attached, and a light-receiving slit with an opening width of 0.3 mm is attached to the light-receiving slit box. Attach the sample plate to the sample table.

FIG. 9 shows an outline of the automatic optical axis adjustment procedure. First, the θ rotation motor is fast-forwarded to bring the sample stage to the position of θ = −90 ° (step 126). In this case, the incident X-ray will pass through the through hole of the optical axis adjusting jig. Next, 2 X-ray tubes
Operate under the conditions of 0 kV and 5 mA (step 12
8). Then, open the X-ray shutter (step 13).
0). Then, the goniometer base position adjustment (step 132), 2θ = zero confirmation (step 134), θ
= Zero adjustment (step 136) is sequentially performed. Finally, the X-ray shutter is closed (step 138), and the optical axis adjustment is completed.

10a to 10c show in detail the procedure for adjusting the goniometer base position. First, 2θ = −3 ° to +3
In the range of °, the detector arm base is scanned while measuring the X-ray intensity (step 140). At that time, the value of 2θ and the X-ray intensity are stored (step 142). Next, it is determined whether or not there is a peak within the above-mentioned scan range (step 144). If there is no peak, an error message is displayed on the CRT display (step 146) and the automatic optical axis adjustment is stopped. If there is a peak, it is determined whether the peak is within the range of 2θ = ± 0.18 ° (step 148). This range is set within the maximum operating range of the goniometer base, as shown in Table 1 above. If there is no peak in this range, an error message is displayed on the CRT display (step 150) and the automatic optical axis adjustment is stopped. If the peak is in this range,
Half the half-value width δ of the peak 151 is calculated and stored (step 152). Next, it is determined whether the position of the peak is on the plus side or the minus side (step 154). When the peak 153 is on the negative side, the process directly proceeds to the procedure of FIG. 10b. When the peak 155 on the plus side is α = 270
Fast-forward the eccentric cam so that
6). The eccentric cam is initially set at the position of α = 0 °. To set α = 270 °, the pulse motor 82
It is sufficient to supply 375 pulses to (Fig. 4). By doing so, in FIG. 5, the cam follower 100 comes to the rightmost position, and the peak 155 on the plus side moves to the minus side. In this way, when adjusting the goniometer base, the peak is always made to approach zero from the negative side to improve the reproducibility of the optical axis adjustment.

Next, in FIG. 10b, the detector arm base is fast-forwarded so that 2θ = (O + δ / 2) ° (step 15).
8). Then, the eccentric cam is slowly scanned (step 160). Then, the negative peak 153 slowly moves to the positive side, and 2θ = (O +
When observed at the position of δ / 2) °, the X-ray intensity gradually increases. Then, it is determined whether the X-ray intensity reaches 40% of the maximum intensity observed so far, that is, the peak height h (step 162). If not reached, the eccentric cam continues to rotate. When it reaches 40%, the eccentric cam is stopped (step 164). At that point, move the detector arm base to move X at the position of 2θ = (O + δ / 2) °.
The line intensity I _p and the X-ray intensity I _m at the position of 2θ = (O−δ / 2) ° are observed and stored (step 166). Next, it is confirmed that the difference between I _p and I _m is sufficiently small. That is, (| I _p −I _m |) / (I _p + I _m ) ≦ 0.0
5 is determined (step 168). If the difference is sufficiently small, it means that the position adjustment of the goniometer base has been completed, and the process proceeds to the confirmation of 2θ = 0 (step 134). At that time, the goniometer base 20 is electromagnetically locked to the plate 18
Fixed to. If the difference between I _p and I _m is not small enough,
Turning to FIG. 10 c, _{I m} is determined greater than _{I p} (step 170). Since the peak is approaching from the minus side, I _m is usually larger than I _p , and at that time, the eccentric cam is slightly rotated by one pulse (step 172). Then, the peak moves slightly to the plus side, and in this state, the step 16 in FIG.
Return to 6. If the intensity of the X-ray source changes during the optical axis adjustment work, the determination in step 170 is not necessarily Y.
Not ES. That is, when the intensity of the X-ray source at the time of measurement in step 162 is smaller than the intensity of the X-ray source at the time of maximum intensity measurement, I _p may be higher than I _m. . At this time, the eccentric cam is rotated by 488 pulses (step 174). That is, the peak is returned to the minus side by 500-488 = 12 pulses. Then, the process starts again from step 166. In any case, finally, the determination in step 168 becomes YES, and the adjustment of the goniometer base is completed.

Next, moving to FIG. 11, it is confirmed that 2θ = 0. First, the detector arm base is scanned while measuring the X-ray intensity in the range of 2θ = −0.12 ° to + 0.12 ° (step 176). The peak position is determined from the peak profile stored at that time and stored (step 178). The position of this peak is the position of 2θ = 0. Therefore, the detector arm base is then rotated to bring 2θ to the peak position (step 180). The detector arm pedestal is now set to the exact 2θ = 0 position. Then, the process proceeds to the adjustment of θ = zero (step 136).

FIG. 12 shows the adjustment procedure for θ = 0. First, the sample stage is rotated from the current position (θ = −90 °) to + 10 ° by fast-forwarding, and preliminary measurement of the peak is performed (step 1
82). Next, in the vicinity of the observed peak position, that is, in the range of θ = (peak position ± 0.02 °), the sample stage is slowly scanned (step 184). Then, the peak position is determined and stored (step 186).
This peak position is the position where θ = zero. Now, θ =
The zero adjustment is completed, and the process returns to step 138 in FIG.

As described above, according to the present invention, the goniometer base, the X-ray detector arm base, and the sample base are driven by the base rotation motor, the 2θ rotation motor, and the θ rotation motor, respectively. Since the motor can be independently controlled by the control device, there is an effect that the optical axis adjustment of the goniometer can be automated.

[Brief description of drawings]

FIG. 1 is a schematic plan view of an X-ray diffractometer having an embodiment of the present invention, FIG. 2 is a front view of a part of which is shown in cross section, and FIG. 3 is a block diagram of a control system of an embodiment of the present invention. 4 and 5 are perspective views of a main part of a goniometer base drive mechanism used in this embodiment, FIG. 5 is an operation explanatory view of this drive mechanism, FIG. 6 is an operation diagram of this drive mechanism, and 7a. FIG. 7 and FIG. 7b are perspective views showing two usage states of the optical axis adjusting jig used in this embodiment, FIG. 8 is a flowchart showing a procedure before and after the automatic optical axis adjusting work, and FIG. 10 is a flowchart showing a procedure for adjusting the position of the goniometer base, FIG. 11 is a flowchart showing a procedure for confirming 2θ = 0, and FIG. 12 is θ = 0. 6 is a flowchart showing the adjustment procedure of FIG. 14 …… X-ray tube 20 …… Goniometer base 22 …… Sample stand 24 …… X-ray detector arm stand 28 …… X-ray detector 40 …… θ rotation motor 42,46 …… Warm wheel 44,48… … Worm 50 …… 2θ rotation motor 58 …… Control device 96 …… Eccentric cam 100 …… Cam follower

Front page continued (72) Inventor Osamu Hirashima 3-9-12 Matsubara-cho, Akishima-shi, Tokyo Inside the Haijima Plant of Rigaku Denki Co., Ltd. (72) Noboru Osawa 3-9-12 Matsubara-cho, Akishima-shi, Tokyo Rigaku Electric Co., Ltd. Haijima Inside the factory (72) Inventor Shigematsu Asano 3-9-12 Matsubara-cho, Akishima-shi, Tokyo Inside Rigaku Denki Co., Ltd. (72) Inventor Hiroshi Kawasaki 3-9-12 Matsubara-cho, Akishima-shi, Tokyo Inside Rigaku Denki Co., Ltd. Haijima factory (72) Inventor Masataka Sakata 3-9-12 Matsubara-cho, Akishima-shi, Tokyo Inside Rijima Electric Co., Ltd. Haijima factory (72) Inventor Kazuyuki Yoshizawa 3-9-12 Matsubara-cho, Akishima-shi, Tokyo Inside Rijima Electric Haijima factory (56 ) References JP-A 1-127940 (JP, A) JP-A 47-45987 (JP, A) JP-B 52-41075 (JP, B2)

Claims (1)

[Claims] 1. A goniometer base rotatable with respect to an X-ray source, an X-ray detector arm base rotatable with respect to the goniometer base and having an X-ray detector attached thereto, and the goniometer. An X-ray diffraction apparatus having a sample stage rotatable with respect to a base, comprising: (a) a base rotation motor, (b) a 2θ rotation motor, (c) a θ rotation motor, and (d) the base A first transmission mechanism that transmits the rotation of a rotation motor to the goniometer base; (e) a second transmission mechanism that transmits the rotation of the 2θ rotation motor to the X-ray detector arm base; and (f) the θ rotation. A third transmission mechanism for transmitting the rotation of the motor to the sample stage, and (g) based on the peak information of the output of the X-ray detector,
An automatic optical axis adjusting device for a goniometer, comprising: a control device that independently controls the base rotation motor, the 2θ rotation motor, and the θ rotation motor.