Patent Number: 
Section: description

Systems are now being adopted for sterilizing various types of articles including food products by radiating the food products. When the food products are relatively narrow, electron beams are now generally being used. The electron beams have especial utility when the articles being irradiated have a thickness within particular limits. For example, electron beams are used to irradiate flat hamburger patties weighing one-quarter of a pound (xc2xc lb) or one-half of a pound (xc2xd lb). Electron beams are generally not effective in irradiating articles having a relatively great width. This results from the fact that the electron beams have weight. This weight causes the electron beams to become decelerated as they pass through the article being irradiated. Thus, the interior of the articles is not irradiated. This is true even when the electron beams enter into the article from two (2) opposite sides of the articles in two (2) successive movements of the article past the radiator. For articles of considerable thicknesses, x-rays are often used to irradiate the articles. X-rays are advantageous because they constitute electromagnetic waves which do not have any mass. As a result, the x-rays are not slowed as they pass through the articles being sterilized. A disadvantage is that a considerable amount of the x-ray energy is not utilized in sterilizing articles when the thickness of the articles is (a) above the range where the articles can be sterilized by electron beams (b) but below the range where the full intensity of the radiation from the x-rays can be efficiently utilized in sterilizing the articles. The preferred embodiment of this invention provides for an efficient use of the full intensities of x-rays in sterilizing relatively thick articles. This efficient use is provided by subjecting the articles initially to the full intensity of the x-ray radiation from an accelerator and subsequently to the reduced intensity remaining after the initial radiation of the articles. The initial and subsequent radiations are provided in a way so that the number of articles radiated per unit of time is not reduced relative to the number of units which are radiated per the unit of time when only the initial radiations are provided. In a preferred embodiment of the invention, a beam of radiation, preferably x-rays, is provided by accelerators generally indicated at 10. The x-rays may be formed in a conventional manner well known in the art. For example, the x-rays may be formed by impinging electrons in an electron beam on a Brehm stalling member such as a member made from titanium. This is well known in the prior art. The beam of x-rays is directed to articles 12 which are transferred from a loading area generally indicated at 14. The articles 12 may have a thickness which is greater than the maximum thickness at which the articles can be irradiated by an electron beam. The articles 12 may be stacked in a queue 16 at a position between the loading area 14 and the position at which the articles are irradiated by the accelerators 10. The release of successive ones of the articles 12 from the queue 16 may be controlled by a microprocessor 18. The loading area 14, the queue 16 and the microprocessor 18 may be constructed in a conventional manner well known to persons of ordinary skill in the art. The articles 12 may be moved by a conveyor system, generally indicated at 20, from the loading area 14 to the position at which the articles are irradiated by the radiation, preferably xrays, from the accelerator 10. The irradiation of the articles 12 is preferably provided within a closed chamber 22. The chamber 20 may be made from a suitable material such as concrete or steel to insulate the space outside of the chamber from the radiation within the chamber. The articles 12 on the conveyor system 20 are transferred to a conveyor system, generally indicated at 24, which is preferably disposed in the form of a loop within the chamber 22. Preferably the conveyor system 24 may be constructed in a conventional manner and is preferably provided in the form of a closed loop. The articles 12 are moved on the conveyor system 24 past the accelerators 10 which direct the radiation from the accelerator against a first side of the articles. The articles 12 are then moved on the conveyor system 24 to apparatus 26 which rotates the articles in a conventional manner through an angle of substantially 180xc2x0. In this way, radiation from the accelerators 10 will be directed against a second side of the articles opposite the first side when the articles are directed by the conveyor system 24 for a second time past the radiation from the accelerators 10. A switch 25 is provided with first and second states of operation. In the first state of operation, the switch 25 provides for a transfer of the loading article 12 in the queue 16 to the conveyor system 24. In the second state of operation, the switch 25 provides for the movement of the article on the conveyor system 24 past the accelerators 10 in a second pass to obtain an irradiation of the x-ray beam through the second side of the article 12 after the article has been rotated through an angle of substantially 180xc2x0. The operation at each instant of the switch 25 in the respective one of the first and second states is controlled by the microprocessor 18. As will be appreciated, the switch 25 operates in the first state for each article 12 to provide for a transfer of the article from the conveyor system 20 to the conveyor system 24. The switch 25 subsequently operates in the second state to provide for the movement of the article 12 a second time past the accelerators 10 to obtain an irradiation of the second side of the article. The times for the operation of the switch 25 in the first and second states are controlled by the microprocessor 18. A switch 28 is provided on the conveyor system 24. The switch 28 may be provided with first and second states of operation under the control of the microprocessor 18. In the first state of operation, the switch 28 provides for the movement of the articles 12 past the apparatus 26 for rotating the articles through the angle of 180xc2x0. In the second state of operation, the switch 28 provides for the transfer of the articles 12 from the conveyor system 24 to a conveyor system, generally indicated at 30. The operation of the switch 28 in the first and second states may be controlled by the microprocessor 18. The switch 28 is initially operated in the first state for each of the articles 12 under the control of the microprocessor 18 and is subsequently operated in the second state for each of the articles 12 under the control of the microprocessor. By providing the switch 28 in the first state of operation and rotating the article 12 through the angle of substantially 180xc2x0, the article 12 on the conveyor system 24 is irradiated from the second side of the article. This causes the cumulative irradiation at the different positions in the article 12 to be, for every position in the article, between maximum and minimum limits. The minimum limit of irradiation intensity is selected to insure that the cumulative irradiation at every position in the article 12 is at least at a level of intensity where harmful bacteria such as E col are destroyed. The maximum limit of irradiation intensity is selected so that beneficial bacteria in the article will not be destroyed. The thickness of the article 12 may sometimes be above a value where the cumulative intensity of the radiation of the article at some positions in the article will be above the maximum intensity of the article irradiation for optimal results even though the intensity of the irradiation of the article at other positions is between the maximum and minimum limits. Under such circumstances, a member may be positioned between the accelerator 10 and the article 12 to absorb some of the radiation intensity from the accelerator at the positions in the article where the intensity of the radiation is above the maximum limit. In this way, the cumulative intensity of the radiation at every position in the articles is between the minimum and maximum optimal values. A system for adjusting the intensity of the irradiation in the article 12 to intensities between the minimum and maximum values is disclosed and claimed in U.S. patent application listing Gary K. Loda and Richard C. Miller as joint inventors and relating to a SYSTEM FOR, AND METHOD OF, IRRADIATING AN OBJECT WITH AN OPTIMAL AMOUNT OF RADIATION. Patent application Ser. No. 09/710,930 is assigned of record to the assignee of record of this patent application. Since x-rays can penetrate the article 12 through relatively great thicknesses, the x-rays can often pass from one side of the article through the article and emerge from the opposite side of the article with a significant intensity. Until now, such x-ray energy has been lost since no use has been made of such energy. This application provides a system for, and method of, utilizing the significant amount of energy passing through each of the articles 12 so as to irradiate the article with this significant amount of energy. In this way, substantially all of the x-ray energy in the radiation beam from the accelerators 10 is used to irradiate the article 12. In irradiating the article 12 twice in this manner, the intensity of the radiation beam from the accelerator 10 can be reduced, thereby minimizing the cost of the accelerator and the cost of providing radiation from the accelerator, when the irradiations of the articles 12 on the conveyor systems 24 and 30 are cumulatively at the desired intensity. To utilize the x-ray energy passing through the article 12 on the conveyor system 30, the switch 28 is operated in the second state after the article has been rotated through an angle of substantially 180xc2x0 by the apparatus 26 and the second side of the article has been irradiated by the x-ray beam from the accelerators 10. In the second state of operation, the switch 28 passes the article 12 to the second conveyor system 30. The second conveyor system 30 is disposed in the thick amber 22. The second conveyor system 30 may be disposed in a loop, preferably closed, similar to the configuration of the conveyor system 24. However, as shown at 29 in the single FIGURE, the article 12 may have to travel through a portion of a loop after it has been transferred from the conveyor 24 and before it reaches the conveyor system 30. At substantially the same time that the article 12 on the first conveyor system 24 is transferred to the second conveyor system 30, an article 12 in the loading area 14 is transferred to the queue 16. At substantially the same time, the leading article 12 in the queue 16 is transferred to the conveyor system 24. The movement of the article 12 from the first conveyor system 24 to the position on the second conveyor system 30 for receiving the x-ray beam passing from the accelerators 10 through the article on the first conveyor system 24 is synchronized with the movement of the article from the queue 16 to the position on the first conveyor system for receiving the x-ray beams from the accelerators 10. This synchronization is provided by the operation of a queue 32 on the second conveyor system. The queue 32 stores articles transferred from the first conveyor system 24 and releases the leading article in the queue for movement to the position for receiving the x-ray beam passing from the accelerators 10 through the article on the first conveyor system. The microprocessor 18 synchronizes the movement of the article 12 from the queue 32 to the position for receiving the x-ray beam passing from the accelerator 10 through the article on the first conveyor system 24. The microprocessor 18 also synchronizes the movement of the article from the queue 16 in the first conveyor system 24 to the position for receiving the radiation from the accelerators 10. In this way, the x-ray beam from the accelerators 10 passes through the article 12 on the first conveyor system 24 and then through the article on the second conveyor system 30. The synchronization by the microprocessor 18 between the movement of each article on the first conveyor system 24 and the article on the second conveyor system 30 is even more sophisticated than indicated in the previous paragraph. This even more sophisticated synchronization is provided by the microprocessor 18. Under the control of the microprocessor 18, the first side of the article 12 on the conveyor system 24 moves past the radiation from the accelerators 10 at the same time that the first side of the article on the conveyor system 30 moves past the radiation passing from the accelerators through the article on the conveyor system 24. In like manner, the second side of the article 12 on the conveyor system 24 moves past the radiation from the accelerators 12 at the same time that the second side of the article on the conveyor system 30 moves past the radiation passing from the accelerators through the article on the conveyor system 24. The synchronous movement of the second sides of the articles 12 on the conveyor systems 24 and 30 past the radiation from the accelerators 10 may be facilitated by providing queues 35 and 37 respectively on the conveyor systems 24 and 30 and by having the microprocessor 18 synchronize the release of the articles from the queues. An apparatus 33 is provided for rotating each article 12 on the conveyor system 30 through an angle of 180xc2x0 after the article has moved a first time past the position for receiving irradiation on the first side of each article on the conveyor system 30 from the accelerators 10 and before the article has moved a second time past the position for receiving irradiation on the second side of the article on the conveyor system 30 from the accelerators 10. The operation of the apparatus 33 in rotating each article 12 through an angle of 180xc2x0 is controlled by the microprocessor 18. A switch 34 having first and second states of operation is provided on the conveyor system 30 at a position past the position where each article 12 on the conveyor system is irradiated with the radiation passing through the article on the conveyor system 24 from the accelerators 10. In the first state, the switch 34 provides for the movement of each article 12 on the conveyor system 30 past the position where the radiation from the accelerator 10 passes through the articles on the conveyor system 24. In the second state, the switch 34 provides for the passage of the articles on the conveyor system 30 to a conveyor system generally indicated at 36. The conveyor system 36 moves the articles 12 to an unloading area generally indicated at 38. The articles 12 are removed from the conveyor system 36 at the unloading area 38. The operation of the switch 34 in the first and second state is controlled by the microprocessor 18. The switch 34 initially operates in the first state to move each article 12 on the conveyor system 30 past the position for irradiating the article with radiation passing through the article on the conveyor system 24 from the accelerator 10. The switch 34 operates in the first state twice so that the article 12 can move twice past the position for receiving radiation from the accelerators 10, the first time for receiving radiation on the first side of the article 10 and the second time for receiving radiation on the second side of the article. The switch 34 subsequently operates in the second state for transferring each article 12 from the conveyor system 30 to the conveyor system 36 and then to the unloading area 38 after the first and second sides of the article on the conveyor system 30 have been irradiated. Radiation shielding material is disposed within the chamber 22 in a strategic relationship to shield the articles 12 from radiation, except at the positions where they receive radiation from the accelerators 10, as the articles move through the chamber 22. For example, the chamber 22 may be defined by radiation shielding material 40. The shielding material 40 may be made from concrete. A radiation shielding member 42 made from a suitable material such as concrete may be disposed within the conveyor system 24 to prevent radiation from the accelerator 10 from passing to the conveyor systems 20 and 36, the loading area 14 and the unloading area 38. The radiation shielding member 42 also prevents radiation from the accelerator 10 from passing to the articles on the conveyor system 30 other than in the area where the radiation from the accelerator 10 passes directly to such articles. The radiation shielding member 42 may extend integrally from the radiation on shielding materials 40. A radiation shielding member 44 made from a suitable material such as concrete may be disposed within the conveyor system 30 to shield the articles on the conveyor system from radiation except where the articles move past the position where the articles receive the radiation passing through the articles on the conveyor system 24 from the accelerators 10. A radiation shielding member 46 made from a suitable material such as concrete may be disposed within the conveyor system 30 to shield the articles 12 as they move on the conveyor system except in the portion of the conveyor system where the articles move past the accelerators 10. Although this invention has been disclosed and illustrated with reference to particular preferred embodiments, the principles involved are susceptible for use in numerous other embodiments which will be apparent to persons of ordinary skill in the art. The invention is, therefore, to be limited only as indicated by the scope of the appended claims.