Patent Number: 
Section: claims

1. A blade device for use in forming a hollow cone-like radiation, the blade device comprising:a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction perpendicular to an axis of the cone;a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone, the second direction perpendicular to the first direction;a pair of lever members each fixed respectively at a first end thereof to a respective face of each the pair of second blade members on the side opposite to a mutually confronting side; anda lever actuating unit configured to pivot the pair of lever members about respective support shafts, wherein the lever actuating unit comprises:a pair of shaft members supported axially movably and unrotatably, the pair of shaft members having outer peripheries formed with thread grooves respectively and being engaged at front end portions thereof with a second end of each of the pair of lever members respectively;a pair of wheels supported axially unmovably and rotatably, the pair of wheels having inner peripheries formed with thread grooves respectively and being threadedly engaged with the pair of shafts respectively;a common entraining member engaged with the pair of wheels; anda driving wheel configured to drive the entraining member. 2. A blade device according to claim 1, wherein the lever actuating unit further comprises a pair of springs configured to urge the second end of each of the pair of lever members toward the pair of shaft members respectively. 3. A blade device according to claim 1, wherein the lever actuating unit further comprises a tension imparting device configured to impart tension to the entraining member. 4. A blade device according to claim 3, wherein the tension imparting device comprises:an idler wheel engaged with the entraining member; anda spring configured to urge an axis of the idler wheel in a direction to expand a loop of the entraining member. 5. A blade device according to claim 4, wherein the pair of wheels, the driving wheel, and the idler wheel each comprises a toothed wheel, and the entraining member is a toothed belt. 6. A blade device for use in forming a hollow cone-like radiation, the blade device comprising:a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction peapendicular to an axis of the cone;a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone, the second direction perpendicular to the first direction;a pair of lever members each fixed respectively at a first end thereof to a respective face of each the pair of second blade members on the side opposite to a mutually confronting side; anda lever actuating unit configured to pivot the pair of lever members about respective support shafts, wherein the lever actuating unit comprises:a ring configured to rotate coaxially with the axis of the cone; anda pair of cam members formed on an end face of the ring so as to engage a second end of each of the pair of lever members. 7. A blade device according to claim 6, wherein the lever actuating unit further comprises a pair of springs configured to urge the second end of each of the pair of lever members toward the cam members respectively. 8. A blade device according to claim 7, wherein the pair of springs comprises a pair of leaf springs. 9. An X-ray imaging apparatus comprising:an X-ray tube;a collimator configured to adjust an irradiation field;an X-ray receiver; anda blade device configured to form a hollow cone-like radiation for excluding off-focal irradiation, the blade device comprising:a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction perpendicular to an axis of the cone;a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone, the second direction perpendicular to the first direction;a pair of lever members each fixed respectively at a first end thereof to a respective face of each the pair of second blade members on the side opposite to a mutually confronting side; anda lever actuating unit configured to pivot the pair of lever members about respective support shafts, wherein the lever actuating unit comprises:a pair of shaft members supported axially movably and unrotatably, the pair of shaft members having outer peripheries formed with thread grooves respectively and being engaged at front end portions thereof with, opposite end portions of the pair of lever members respectivelya pair of wheels supported axially unmovably and rotatably, the pair of wheels having inner peripheries formed with thread grooves respectively and being threadedly engaged with the pair of shafts respectively;a common entraining member engaged with the pair of wheels; anda driving wheel configured to drive the entraing member. 10. An X-ray imaging apparatus according to claim 9, wherein the lever actuating unit further comprises a pair of springs configured to urge a second end of each of the pair of lever members toward the pair of shaft members respectively. 11. An X-ray imaging apparatus according to claim 9, wherein the lever actuating unit further comprises a tension imparting device configured to impart tension to the entraining member. 12. A blade device according to claim 11, wherein the tension imparting device comprises:an idler wheel engaged with the entraining member; anda spring configured to urge an axis of the idler wheel in a direction to expand a loop of the entraining member. 13. An X-ray imaging apparatus according to claim 12, wherein the pair of wheels, the driving wheel, and the idler wheel each comprises a toothed wheel, and the entraining member is a toothed belt. 14. An X-ray imaging apparatus comprising:an X-ray tube;a collimator configured to adjust an irradiation field;an X-ray receiver; anda blade device configured to form a hollow cone-like radiation for excluding off-focal irradiation, the blade device comprising:a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction perpendicular to an axis of the cone;a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone, the second direction perpendicular to the first direction;a pair of lever members each fixed respectively at a first end thereof to a respective face of each the pair of second blade members on the side opposite to a mutually confronting side; anda lever actuating unit configured to pivot the pair of lever members about respective support shafts, wherein the lever actuating unit comprises:as ring configured to rotate coaxially with the axis of the cone; anda pair of cam members formed on an end face of the ring so as to engage a second end of each of the pair of lever members. 15. An X-ray imaging apparatus according to claim 14, wherein the lever actuating unit further comprises a pair of springs configured to urge the second end of each of the pair of lever members toward the cam members respectively. 16. An X-ray imaging apparatus according to claim 15, wherein the pair of springs comprises a pair of leaf springs. 17. A method of assembling a blade device for use in forming a hollow cone-like radiation, the method comprising:positioning a pair of first blade members opposed to each other symmetrically at a fixed inclination angle in a first direction perpendicular to an axis of the cone;positioning a pair of second blade members opposed to each other symmetrically at a variable inclination angle in a second direction perpendicular to the axis of the cone, the second direction perpendicular to the first direction;fixedly coupling each of a pair of lever members at a respective first end thereof to a respective face of each of the pair of second blade members on the side opposite to a mutually confronting side;coupling a lever actuating unit to the pair of lever members, the lever actuating unit configured to pivot the pair of lever members about respective support shafts;coupling a pair of shaft members to the lever members, the pair of shaft members supported axially movably and unrotatably and having outer peripheries formed with thread grooves respectively and being engaged at front end portions thereof with a second end of each of the pair of lever members respectively;coupling a pair of wheels to the pair of shafts, the pair of wheels supported axially unmovably and rotatably and having inner peripheries formed with thread grooves respectively and being threadedly engaged with the pair of shafts respectively;coupling a common entraining member to the pair of wheels; andcoupling a driving heel to the entraining member.