Abstract:
A stimulable phosphor sheet transfer apparatus for transferring a stimulable phosphor sheet storing therein a radiation image information in a sub-scanning direction when the stimulable phosphor sheet is scanned with a stimulating ray along a main scanning line substantially perpendicular to the sub-scanning direction to emit light in the pattern of the stored radiation energy, the light emitted from the stimulable phosphor sheet being detected to obtain an image information signal, comprises a transfer belt for transferring the stimulable phosphor sheet in the sub-scanning direction, and first and second suction boxes disposed below the transfer belt and adapted to provide a suction force for attracting the stimulable phosphor sheet against the transfer belt. The first and second suction boxes are respectively disposed upstream and downstream of the main scanning line with respect to the sub-scanning direction. Said first and second suction boxes are separately connected to a suction blower respectively by way of switching valves, and a pair of buffer tanks are provided respectively between the first suction box and the switching valve corresponding thereto and between the second suction box and the switching valve corresponding thereto.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a stimulable phosphor sheet transfer apparatus for transferring a stimulable phosphor sheet in a radiation image recording/reproducing system in which the stimulable phosphor sheet is exposed to radiation through an object and is scanned with a stimulating ray to emit light in the pattern of the stored energy of radiation, and more particularly to a stimulable phosphor sheet transfer apparatus for transferring a stimulable phosphor sheet in such a radiation image recording/reproducing system during radiation image information reading operation in which the light emitted from the stimulable phosphor sheet upon exposure to the stimulating ray is detected to obtain an image signal. 
     2. Description of the Prior Art 
     When certain kinds of phosphors are exposed to radiation such as X-rays, α-rays, β-rays, γ-rays, cathode rays or ultraviolet rays, they store a part of the energy of the radiation. Then when the phosphor which has been exposed to the radiation is exposed to a stimulating ray such as a visible ray, light is emitted from the phosphor in the pattern of the stored energy of the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor and a sheet material bearing thereon a stimulable phosphor layer is referred to as a &#34;stimulable phosphor sheet&#34; and can be used as a recording medium for recording thereon a radiation image information. 
     There has been proposed a radiation image information recording/reproducing system in which a radiation image of an object is once recorded on a stimulable phosphor sheet as a pattern of stored energy of radiation, the stimulable phosphor sheet is scanned with a stimulating ray, and light emitted from the stimulable phosphor sheet is photoelectrically detected to obtain an image signal which is subsequently processed to reproduce a visible radiation image of the object. For example, see Japanese Unexamined Patent Publication No. 56(1981)-11395, U.S. Pat. Nos. 4,258,264, 4,315,318, 4,387,428 and 4,276,473. The image signal can be reproduced as a hard copy or a visible image on a cathode ray tube, for instance. 
     FIG. 1 shows an example of a radiation image information reading device for use in such radiation image recording/reproducing systems. 
     In FIG. 1, a laser beam 1a (as the stimulating ray) of a predetermined intensity emitted from a laser source 1 is caused to impinge upon a galvanometer mirror 2. The laser beam 1a is deflected, as indicated at 1b, by the galvanometer mirror 2 to sweep a stimulable phosphor sheet 3 below the galvanometer mirror 2 in the direction of arrow A (main scanning) while the stimulable phosphor sheet 3 is transferred by an endless belt 9 in the direction of arrow B (sub-scanning) perpendicular to the direction of the main scanning. That is, the stimulable phosphor sheet 3 is two-dimensionally scanned with the deflected laser beam 1b. The parts of the stimulable phosphor sheet 3 exposed to the stimulating laser beam 1b emit light according to the energy of radiation stored therein. The light emitted from the stimulable phosphor sheet 3 upon exposure to the stimulating laser beam 1b enters a light guide member 4 having a light incident face 4a disposed near the stimulable phosphor sheet 3 to extend in parallel to the main scanning line. The light guide member 4 is flat in shape at the front portion 4b thereof and substantially cylindrical at the rear portion 4c thereof. To the rear portion 4c of the light guide member 4 is connected a photomultiplier 5 and the light entering the light guide member 4 from the light incident face 4a impinges upon the photomultiplier 5. The photomultiplier 5 converts the light into an electric signal and delivers it to an image signal information processing circuit 6. The image signal thus obtained is reproduced as a visible image on a CRT 7 or stored in a magnetic recording tape in this particular example. 
     If an end portion of the stimulable phosphor sheet 3 curls upward away from the surface of the endless belt 9 or an intermediate portion of the stimulable phosphor sheet 3 is raised upward from the surface of the endless belt 9 while the stimulable phosphor sheet 3 is transferred to be two-dimensionally scanned with the stimulating laser beam 1b in order to read the radiation image information stored in the stimulable phosphor sheet 3, the image to be read can be distorted and the stimulable phosphor sheet 3 can be interfered with the light guide member 4. In order to keep flat the stimulable phosphor sheet 3 during transfer for reading the radiation image information, suction force is applied to the stimulable phosphor sheet 3 through the endless belt 9. That is, as shown in FIG. 2, a large number of small holes are provided in the endless belt 9 and a negative pressure generated in first and second suction boxes 10a and 10b below the upper run of the endless belt 9 is applied to the stimulable phosphor sheet 3 through the holes to attract the stimulable phosphor sheet 3 against the surface of the endless belt 9. If only one suction box is provided below the upper run of the endless belt 9, the negative pressure applied to the stimulable phosphor sheet 3 will fluctuate until the stimulable phosphor sheet 3 comes to entirely cover the suction box. This is the reason why a pair of suction boxes 10a and 10b are provided. That is, the first and second suction boxes 10a and 10b bound with each other along the scanning line of the stimulating laser beam 1b. No negative pressure is generated until the leading edge of the stimulable phosphor sheet 3 reaches the downstream edge of the first suction box 10a, i.e., until the first suction box 10a is entirely covered with the stimulable phosphor sheet 3. Thereafter, when the second suction box 10b is entirely covered with the stimulable phosphor sheet 3, the negative pressure in the first suction box 10a is removed and a negative pressure is generated in the second suction box 10b. The negative pressure in the second suction box 10b is maintained until scanning of the stimulable phosphor sheet 3 with the stimulating laser beam 1b is completed. Thus, the stimulable phosphor sheet 3 is kept in close contact with the surface of the endless belt 9 by a negative pressure applied by one of the suction boxes 10a and 10b from the beginning to the end of scanning of the stimulable phosphor sheet 3. 
     As shown in FIG. 3A, at the time tl when the second suction box 10b - is entirely covered with the stimulable phosphor sheet 3, the negative pressure in the first suction box 10a is abruptly lowered from a predetermined value Pl to zero and at the same time, a negative pressure of the predetermined value Pl is abruptly generated in the second suction box 10b. This is to reduce fluctuation in load on the transfer means. That is, when the stimulable phosphor sheet 3 is attracted against the endless belt 9 under the force of negative pressure, load is exerted on the transfer means including the endless belt due to resistance produced between the endless belt and the suction box in operation, and accordingly the load on the transfer means fluctuates with the number of suction box in operation. 
     However, when the pressures in the first and second suction boxes 10a and 10b are abruptly changed in the manner described above, transfer speed of the stimulable phosphor sheet 3 changes to cause density fluctuation in a reproduced image in the direction of the sub-scanning. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing observations and description, the primary object of the present invention is to provide a stimulable phosphor sheet transfer apparatus in which the load on the transfer apparatus and the transfer speed of the stimulable phosphor sheet experience substantially no change throughout the reading operation in the radiation image reading/reproducing system. 
     The stimulable phosphor sheet transfer apparatus in accordance with the present invention is for transferring a stimulable phosphor sheet storing therein a radiation image information in a sub-scanning direction when the stimulable phosphor sheet is scanned with a stimulating ray along a main scanning line substantially perpendicular to the sub-scanning direction to emit light in the pattern of the stored radiation energy, the light emitted from the stimulable phosphor sheet being detected to obtain an image information signal, and comprises a transfer belt for transferring the stimulable phosphor sheet in the sub-scanning direction, and first and second suction boxes disposed below the transfer belt and adapted to provide a suction force for attracting the stimulable phosphor sheet against the transfer belt, the first and second suction boxes being respectively disposed upstream and downstream of the main scanning line with respect to the sub-scanning direction, 
     characterized, in one aspect of the present invention, in that said first and second suction boxes are separately connected to a suction blower respectively by way of switching valves, and a pair of buffer tanks are provided respectively between the first suction box and the switching valve corresponding thereto and between the second suction box and the switching valve corresponding thereto. 
     In another aspect, the stimulable phosphor sheet transfer apparatus of the present invention is characterized in that said first and second suction boxes are communicated with separate suction blowers. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic view showing an example of the radiation image recording/reproducing system in which the stimulable phosphor sheet transfer apparatus in accordance with the present invention is employed, 
     FIG. 2 is a fragmentary side view showing a part of the radiation image recording/reproducing system of FIG. 1, 
     FIGS. 3A and 3B are graphs for illustrating the difference between the operation of the stimulable phosphor sheet transfer apparatus of the present invention and that of the conventional stimulable phosphor sheet transfer apparatus, 
     FIG. 4 is an air circuit diagram of a stimulable phosphor sheet transfer apparatus in accordance with an embodiment of the present invention, and 
     FIG. 5 is an air circuit diagram of a stimulable phosphor sheet transfer apparatus in accordance with another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A stimulable phosphor sheet transfer apparatus in accordance with a first embodiment of the present invention will be described with reference to FIG. 4. The stimulable phosphor sheet transfer apparatus of this embodiment differs from the stimulable phosphor sheet transfer apparatus shown in FIGS. 1 and 2 in the air circuit for providing suction force to the first and second suction boxes, and accordingly description will be made mainly on the air circuit, hereinbelow. In FIG. 4, the parts corresponding to the parts shown in FIGS. 1 to 3 are given the same reference numerals. The first suction box 10a has a first compartment Sl and a second compartment S2 and similarly, the second suction box 10b has a first compartment S3 and a second compartment S4. When the stimulable phosphor sheet to be transferred is relatively small in width, only the first compartment of the first suction box 10a and the first compartment of the second suction box 10b are connected to a suction blower 11 to be described later. On the other hand, when the stimulable phosphor sheet to be transferred is relatively large in width, both the compartments Sl and S2 of the first suction box 10a and both the compartments S3 and S4 of the second suction box 10b are connected to the suction blower 11. This switching is accomplished by solenoid valves V2 and V4 as will become apparent later. 
     An air passage Ll extends from the suction blower 11 and an air passage L3 is connected to the air passage Ll at one end. To the other end of the air passage L3 are connected air passages L4 and L5 respectively extending from the first compartment Sl and the second compartment S2 of the first suction box 10a. A solenoid valve Vl for closing and opening the air passage L3 is disposed in the air passage L3, and said solenoid valve V2 is disposed in the air passage L5. An air passage L7 is connected to the air passage Ll at one end. To the other end of the air passage L7 are connected air passages L8 and L9 respectively extending from the first compartment S3 and the second compartment S4 of the second suction box 10b. A solenoid valve V3 for closing and opening the air passage L7 is disposed in the air passage L7, and said solenoid valve V4 is disposed in the air passage L9. 
     An air passage L2 is connected to the air passage Ll at one end and opens to the atmosphere by way of an orifice 14 at the other end. A suction force changing solenoid valve V0 is disposed in the air passage L2 between the junction of the air passage L2 to the air passage Ll and the orifice 14. The suction force or the negative pressure provided to the air passage Ll is changed between &#34;strong&#34; and &#34;weak&#34; by opening and closing the suction force changing solenoid valve V0. The air passage L3 is connected to a first buffer tank 12 by way of an air passage L6 and the air passage L7 is connected to a second buffer tank 13 by way of an air passage L10. 
     In FIG. 2, the stimulable phosphor sheet 3 bearing thereon a radiation image information is fed to the endless belt 9 from the right side as shown in FIG. 2 and is transferred on the endless belt 9. At this time the solenoid valve Vl is opened and the suction blower 11 is communicated with the compartments Sl and S2 of the first suction box 10a  by way of the air passages Ll, L3, L4 and L5 to provide a suction force to the stimulable phosphor sheet 3 through the small holes in the endless belt 9 to attract the stimulable phosphor sheet 3 against the endless belt 9. When the stimulable phosphor sheet 3 is relatively small in width, the solenoid valves V2 and V4 are closed not to provide suction force to the compartments S2 and S4 irrespective of opening and closure of the solenoid valves Vl and V3. Until the leading edge 3a of the stimulable phosphor sheet 3 reaches the scanning line of the stimulating ray 1b, reading of the radiation image information is not effected and accordingly change in transfer speed does not affect reading of the image information. Therefore, the suction force changing solenoid valve V0 is closed to increase the suction force applied to the stimulable phosphor sheet 3 so that the stimulable phosphor sheet 3 can be attracted against the endless belt 9 with a sufficient force even if the first suction box 10a (the compartments Sl and S2, or the compartment Sl) is not entirely covered with the stimulable phosphor sheet 3 and so that the stimulable phosphor sheet 3 can be positively attracted against the endless belt 9 even if the stimulable phosphor sheet 3 curls away from the surface of the endless belt 9. 
     After the leading edge 3a of the stimulable phosphor sheet 3 reaches the scanning line of the stimulating ray 1b and immediately before starting of reading of the radiation image information, the suction force changing solenoid valve V0 is opened to permit draw of air from the outside by way of the orifice 14 and the negative pressure in the air passage Ll is adjusted to a predetermined value determined by the diameter of the orifice 14. Since the first suction box 10a is entirely covered with the stimulable phosphor sheet 3 at this time, the stimulable phosphor sheet 3 is attracted against the endless belt 9 by the suction force applied thereto through the small holes in the endless belt from the entire area of the suction box 10a, whereby the part of the stimulable phosphor sheet 3 to be scanned is kept flat. 
     In this condition, the stimulable phosphor sheet 3 is transferred by the endless belt 9, and after the stimulable phosphor sheet 3 comes to entirely cover the second suction box 10b (the first and second compartments S3 and S4, or the first compartment S3), and while the stimulable phosphor sheet 3 still entirely covers the first suction box 10a, the solenoid valve Vl is closed and the solenoid valve V3 is opened to interrupt feeding of the suction force to the first suction box 10a and to start feeding of the suction force to the second suction box 10b. Thus, the negative pressure in the first suction box 10a is reduced to zero, and the second suction box 10b is provided with a negative pressure of the predetermined value Pl. However, in this embodiment, the pressures in the respective suction boxes 10a and 10b gradually change as shown in FIG. 3B. The rates of change in the pressure in the suction boxes 10a and 10b depends upon the capacity of the suction blower 11 and the volumes of the buffer tanks 12 and 13. By gradually changing the pressure in the suction boxes 10a and 10b, change in the transfer speed can be prevented. 
     Now, a stimulable phosphor sheet transfer apparatus in accordance with a second embodiment of the present invention will be described with reference to FIG. 5. Also the stimulable phosphor sheet transfer apparatus of this embodiment differs from the stimulable phosphor sheet transfer apparatus shown in FIGS. 1 and 2 in the air circuit for providing suction force to the first and second suction boxes, and accordingly description will be made mainly on the air circuit, hereinbelow. In FIG. 5, the parts corresponding to the parts shown in FIGS. 1 to 3 are given the same reference numerals. The first suction box 10a has a first compartment Sl and a second compartment S2 and similarly, the second suction box 10b has a first compartment S3 and a second compartment S4. When the stimulable phosphor sheet to be transferred is relatively small in width, only the first compartment of the first suction box 10a and the first compartment of the second suction box 10b are provided with a suction force. On the other hand, when the stimulable phosphor sheet to be transferred is relatively large in width, both the compartments Sl and S2 of the first suction box 10a and both the compartments S3 and S4 of the second suction box 10b are provided with a suction force. This switching is accomplished by solenoid valves SVl and SV2 as will become apparent later. 
     An air passage L21 extends from a first suction blower llA and air passages L23 and L24 are connected to the air passage L21 at one end. The other ends of the air passage L23 and L24 are respectively connected to the first compartment Sl and the second compartment S2 of the first suction box 10a. Said solenoid valve SVl is disposed in the air passage L24. An air passage L22 is connected to the air passage L21 at one end and opens to the atmosphere by way of an orifice 14&#39; at the other end. A suction force changing solenoid valve V0&#39; is disposed in the air passage L22 between the junction of the air passage L22 to the air passage L21 and the orifice 14&#39;. The suction force or the negative pressure provided to the air passage L21 is changed between &#34;strong&#34; and &#34;weak&#34; by opening and closing the suction force changing solenoid valve V0&#39;. 
     An air passage L25 extends from a second suction blower llB and air passages L27 and L28 are connected to the air passage L25 at one end. The other ends of the air passage L27 and L28 are respectively connected to the first compartment S3 and the second compartment S4 of the first suction box 10a. Said solenoid valve SV2 is disposed in the air passage L28. An air passage L26 is connected to the air passage L25 at one end and opens to the atmosphere by way of an orifice 14&#34; at the other end. 
     In FIG. 2, the stimulable phosphor sheet 3 bearing thereon a radiation image information is fed to the endless belt 9 from the right side as shown in FIG. 2 and is transferred on the endless belt 9. At this time the first suction blower llA is operated to generate a suction force which is applied by way of the first suction box 10a to the stimulable phosphor sheet 3 through the small holes in the endless belt 9 to attract the stimulable phosphor sheet 3 against the endless belt 9. When the stimulable phosphor sheet 3 is relatively small in width, the solenoid valves SVl and SV2 are closed not to provide suction force to the compartments S2 and S4. Until the leading edge 3a of the stimulable phosphor sheet 3 reaches the scanning line of the stimulating ray lb, reading of the radiation image information is not effected and accordingly change in transfer speed does not affect reading of the image information. Therefore, the suction force changing solenoid valve V0&#39; is closed to increase the suction force applied to the stimulable phosphor sheet 3 so that the stimulable phosphor sheet 3 can be attracted against the endless belt 9 with a sufficient force even if the first suction box 10a (the compartments Sl and S2, or the compartment Sl) is not entirely covered with the stimulable phosphor sheet 3 and so that the stimulable phosphor sheet 3 can be positively attracted against the endless belt 9 even if the stimulable phosphor sheet 3 curls away from the surface of the endless belt 9. 
     After the leading edge 3a of the stimulable phosphor sheet 3 reaches the scanning line of the stimulating ray 1b and immediately before starting of reading of the radiation image information, the suction force changing solenoid valve V0&#39; is opened to permit draw of air from the outside by way of the orifice 14&#39; and the negative pressure in the air passage L21 is adjusted to a predetermined value determined by the diameter of the orifice 14&#39;. Since the first suction box 10a is entirely covered with the stimulable phosphor sheet 3 at this time, the stimulable phosphor sheet 3 is attracted against the endless belt 9 by the suction force applied thereto through the small holes in the endless belt from the entire area of the suction box 10a, whereby the part of the stimulable phosphor sheet 3 to be scanned is kept flat. 
     In this condition, the stimulable phosphor sheet 3 is transferred by the endless belt 9, and after the stimulable phosphor sheet 3 comes to entirely cover the second suction box 10b (the first and second compartments S3 and S4, or the first compartment S3), and while the stimulable phosphor sheet 3 still entirely covers the first suction box 10a, the first suction blower llA is stopped and the second suction blower llB is operated to interrupt feeding of the suction force to the first suction box 10a and to start feeding of the suction force to the second suction box 10b. Thus, the negative pressure in the first suction box 10a is reduced to zero, and the second suction box 10b is provided with a negative pressure of the predetermined value Pl. However, in this embodiment, the pressures in the respective suction boxes 10a and 10b gradually change as shown in FIG. 3B since the first suction blower llA gradually reduces its rotational speed after it is deenergized and the second suction blower 11B increases its rotational speed when it is energized. By gradually changing the pressure in the suction boxes 10a and 10b, change in the transfer speed can be prevented.