Abstract:
A telescoping mast assembly having a ball drive actuator drive system. A telescoping mast section is housed within a base mast section mounted to a base plate. The base mast section pivots about a pivot axis between a lowered, horizontal position and an upright, vertical position and includes an upper elongate body disposed an upper side of the pivot axis and a bottom end disposed on an opposite side of the pivot axis. A ball actuator drive includes an electrically powered motor that drives a ball screw reciprocally inward and outward along a linear stroke path. A remote end of the ball screw is attached to the bottom end of the base mast section and, by pushing and pulling the bottom end of the base mast section, pivots and maintains the base mast section to alternative positions between the fully raised and the fully lowered positions. A telescoping mast section is housed within the base mast section and telescopes between an extended position and a retracted position. A secondary ball screw actuator is housed within the base mast section and is coupled to drive the telescoping mast section between its extended and retracted positions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a telescoping mast assembly useful in sundry applications and, more specifically, to a telescoping mast assembly suitable for mobile field use. 
     2. The Prior Art 
     Telescoping masts are well known safety devices useful in law enforcement, industrial, military or commercial applications. Such masts are portable devices which can be readily deployed when needed and readily returned to a storage position when not in use. Typical applications are those in which equipment or devices require elevation in order to optimally accomplish their intended function. It may be desirable, or essential, to elevate floodlights, cameras, antennas, or other surveillance equipment by means of a telescopic mast assembly in order for such devices to function optimally. By way of example, one common application is to mount a telescopic light mast upon the roof of a vehicle for illuminating a wide area surrounding the vehicle. The mast must quickly and reliably deploy when necessary, and retract against the roof of the vehicle when not in use. Law enforcement officials, in particular, have found such devices useful in the field. 
     Heretofore, telescoping masts have been either pneumatically, hydraulically, or chain driven. Pneumatic drive motors require airtight seals between telescopic mast sections in order to function as intended. However, the environment in which such masts are used makes maintaining an airtight condition between mast sections problematic. Contaminants, or radial ice, deposited between mast sections, or at the junction will stop the mast from descending or cause damage to the mast sections, and can easily destroy the seal required for efficient operation of the pneumatic drive. In the event that the pneumatic integrity of the seal is destroyed, the mast will fall gravity with a potential for disastrous consequences. 
     A further disadvantage to pneumatically powered telescoping masts is that they can only assume one of two positions. Either the masts are fully extended or fully retracted. In many applications, however, because of obstructions or other considerations, it is desirable to have the telescoping mast sections in a partial state of extension or retraction. A further disadvantage with pneumatic drives is that they are relatively heavy in weight, limiting their suitability for vehicle roof applications. In addition, such drives are expensive to manufacture, assemble, and maintain, which limits their commercial appeal. 
     Finally, in applications where the unit is used on uneven terrain, pneumatic units cannot work consistently on grades exceeding fifteen degrees and, if the loading at the top is high, even less. The tubes on pneumatic masts on slopes exceeding the limit may bend at the joint, causing air leakage at the junction and a corresponding failure. A unit accordingly is needed which can safely maintain structural integrity on slopes exceeding fifteen degrees. 
     Hydraulic systems for elevating masts suffer from many of the same shortcomings. Hydraulic drives are relatively heavy in weight and are expensive to manufacture, assemble, and maintain. Moreover, such drives are vulnerable to damage from contact with the environment since hydraulic lines are exposed. Additionally, contaminants can infiltrate the hydraulic system and cause malfunction or failure. 
     Chain driven telescopic masts likewise suffer from the same deficiencies. The drive mechanisms are relatively heavy in weight and are expensive to manufacture, assemble, and maintain. The chain link mechanism is also exposed and susceptible to damage from contact with environmental objects. 
     Other shortcomings common to the aforementioned conventional telescopic mast drives and devices are that the wiring to the outboard end of the mast is exposed and can be damaged by inadvertent contact with surrounding obstacles or suffer from damage from exposure to the elements. Moreover, the masts are generally fabricated from conductive material from the base to the top end. An electrical charge introduced into such, masts from inadvertent contact with exposed overhead electrical lines will, accordingly, be transferred to the vehicle below, causing a potential for danger to the operators on the ground. Available systems lack effective means for preventing such a charge transfer, such as a fuse system. However, even were fuses implemented into wiring of available units, because the wiring is exposed to the elements, such fuses would be prone to damage and deterioration from exposure to the elements and may not function as intended when they are needed. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the aforementioned deficiencies in available telescoping mast systems by providing a ball actuator drive system. A telescoping extendible mast section is housed within a base mast section which mounts to a base plate. A first ball actuator mounts to the base plate and drives the base mast section between a horizontal storage position and a vertical work position. The base plate ball actuator comprises an electrically powered motor which drives a ball screw along a stroke path. A remote end of the ball screw is attached to a bottom end of the base mast section and pivots the base mast into alternative angles of elevation by pushing and pulling against the bottom end of the base mast section. The base mast section can, accordingly, be placed and held in any angle required between the storage and work positions. 
     The telescoping extendible mast section is likewise driven between an extended position and a retracted position by a second ball actuator drive system. The second drive system is fixedly mounted within the base mast section and comprises a drive screw affixed at a remote end to the extendible mast section. Movement of the drive screw along a stroke path pushes and pulls the extendible mast section into alternative positions between the extended and retracted positions. The extendible mast section can, as with the base mast section, be placed and maintained in any of the alternative positions to conform to the physical constraints of the space in which the mast is used. The extension of the extendible mast section is independent of the elevational operation of the base mast section, affording the user a wide range of options for optimally positioning the telescoping mast. Positive actuation of the mast sections in both directions by the drive motors will operate effectively on slopes of twenty degrees or more. 
     Additional stages of telescoping mast sections may be employed in order to increase the maximum reach of the mast. A ball drive actuator for each such additional section can be likewise utilized. The mast sections and ball drive actuators are relatively light weight and are readily assembled and maintained. In addition, the wiring which supplies power and control signals to the ball drive actuators and to electrical devices mounted to a remote end of the mast assembly is housed entirely within the axial passageway of the coaxial mast sections. Protected from exposure to the elements, or damage from contact with surrounding objects, degradation or damage to the wiring is avoided. 
     The top section of the mast is composed of non-electrically conductive material in a preferred embodiment. Such a composition prevents that section from transferring an electrical charge to the vehicle to which the mast assembly is mounted. Danger to operators below from inadvertent contact between the remote section of the mast and exposed overhead conductors is, thereby, avoided. Further, inasmuch as the wiring to the top of the mast is protected within the mast sections from the elements and from damaging contact with environmental obstructions, an effective and reliable fuse system can be incorporated into the wiring harness which will stop the transfer of electrical current from the wires into the base of the unit and therefrom into the vehicle frame. 
     Accordingly, it is an objective of the present invention to provide a telescoping mast assembly having an improved drive system for motivating a plurality of mast sections between storage and work positions, and into alternative positions therebetween. 
     A further objective of the invention is to provide a telescoping mast system having means for encasing and protecting wiring which is routed from the base to the remote end of the mast. 
     Yet a further objective is to provide a telescoping mast system having a positive drive mechanism associated with each mast section, which independently pushes and pulls its respective mast section between an up and a down position, and into alternative positions therebetween. 
     Another objective is to provide a telescoping mast system having improved means for electrically isolating the underlying vehicle on which the mast system is mounted. 
     Still a further objective is to provide a telescoping mast system which is relatively lightweight and protected from deterioration due to exposure to the elements. 
     A further objective is to provide a telescoping mast system comprised of relatively inexpensive components which are economically and readily assembled and easily maintained. 
    
    
     These and other objectives, which will be apparent to those skilled in the arts, are achieved by a preferred embodiment which is described in detail below and which is illustrated by the accompanying drawings. 
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a right front perspective view of the subject telescoping mast system shown in the raised position. 
     FIG. 2 is an exploded perspective view thereof. 
     FIG. 3 is a side elevational view thereof. 
     FIG. 4 is a top plan view thereof. 
     FIG. 5 is a side elevational view, partially in section, of the ball drive actuator for the base mast section. 
     FIG. 6 is an enlarged perspective view of ball drive portion of the ball drive actuator for the base mast section. 
     FIG. 7 is a side elevational view, shown partially in section, of the ball drive actuator for the extendible mast section. 
     FIG. 8 is a perspective view, shown partially in phantom, of an alternative three stage telescoping mast configured according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring first to FIGS. 1 and 2, the subject telescoping mast assembly  10  is shown comprising, generally, a base mounting plate  12 ; a first drive motor  14 ; a base mast section  16 ; a second drive motor  18 ; an extendible mast section  20 ; a motorized light assembly  22 ; and two lamps  24 ,  26 . The base plate is fabricated from steel or other suitably strong material and includes an upper surface  28 , four rearward mounting apertures  30 , and four forward mounting apertures  32 . The base plate  12  is intended to further include means (not shown) for attachment to a vehicle surface, most commonly a roof. Means for attachment is conventionally by welding. 
     Continuing, with reference to FIGS. 5 and 6, the first drive motor  14  is preferably a ball actuator of a type available in the industry. By way of example, without intending to limit the scope of the invention, a suitable ball actuator is manufactured and sold by Motion Systems Corporation located at 600 Industrial Way West, Eatontown, N.J. 07724 under part number 85152. The ball actuator comprises a motor housing  24  and a gear box housing  36 , a worm shaft  38  having threads  39 , and a ball drive screw  40 . The screw  40  includes a geared epicyclic ball  42  at an inboard end across which gear teeth  44  are spaced. A tubular cover  46  encases the ball drive screw  40  forward to a ball screw forward end  48 . Extending forward from the end  48  is an attachment eyelet  50 . 
     The stroke of the screw  40  is selected to correspond with the pivoting of the base mast section between a horizontal, “down”, position and a vertical “up” position as shown in FIG.  3 . The loading of the Model 85152 motor of the preferred embodiment is recommended at five hundred pounds or less. The basic construction of the ball actuator  14  incorporates a high efficiency 0.653 inch diameter epicyclic ball screw  40  with integral freewheeling at stroke ends to eliminate the need for limit switches. 
     The actuator  14  transmits thrust with the epicyclic ball screw  40 . Stop pins are provided (not shown) at each end of travel to initiate freewheel and linear advancement stops at those points. The epicyclic ball screw  40  thus moves along a reciprocal linear path to push and pull against the base mast section as will be explained below. 
     Motor speed reduction to drive the ball drive  40  is by means of a single stage worm gear reducer. The worm shaft  38  runs in a bearing at the motor end and a ball bearing at the opposite end and drives the ball screw  40 . Both the worm and gear are fabricated from heat treated steel and are sealed and permanently lubricated. The reduction ratio utilized is preferably 10:1 but other ratios can be utilized to vary the stroke speed. 
     The motor  24  is electrically powered in the preferred embodiment. For vehicle usage, the motor  24  can be 12VDC; however, for other applications an AC configuration is available. The stroke length of the ball screw  40  is preferably eight and one-half inches; however other stroke lengths may be designed into the telescoping mast assembly within the teachings of the invention. 
     The cover  46  is fabricated from aluminum with a ring seal at its outboard end in order to protect the screw  40 . The ball screw end  50  is self-aligning and a weatherproof motor enclosure is provided to protect the motor from the elements. 
     With reference to FIGS. 1 and 2, the gear box  36  is mounted to the base plate  12  top surface  28  by means of L-shaped brackets  52 ,  54  which attach through apertures  30  of the plate  12  by means of screws  31 , and into the motor housing  36  by screws  55 . A base mast support arm  58  is provided, formed of steel stock and having a square cross sectional axial passageway  59  therethrough. The support arm  58  comprises an upper surface  60 , a centrally disposed aperture  61  extending through a rearward facing side, and a lower rearward facing edge  62 . A pair of spaced apart steel pivot arms  63  are affixed to the lower edge  62  of support arm  58 , by a welded joint or other suitable means, and depend downward therefrom at a substantially 45 degree angle. A pair of end covers  64  are also provided for attachment to the opposite ends of arm  58  and each cover  64  is provided with a centrally disposed through aperture  66 . A connector pin  65  is further provided to affix the end  50  of ball screw  40  to the arms  63  as shown. 
     A pair of mounting L-shaped brackets  68 ,  70  are included in the assembly, each having a central aperture  72  in an upstanding portion and a pair of apertures  74  in a horizontal portion. The brackets  68 ,  70  are preferably fabricated of stainless steel stock and affix to outward sides of the covers  64 . Aperture  72  of the brackets  68 ,  70  align with a respective aperture  66  of: the covers  68 , 70  and pivot pins  76  are provided to project through the coaligned apertures, whereby pivotally joining the support arm  58  to brackets  68 , 70 . Screws  78  project through the apertures  74  and into apertures  32  of the base plate  12  to secure the brackets  68 , 70  to the base plate. The arms  63  are affixed, preferably by welding, to the lower front edge  62  of the support arm  58  and provide the means through which member  58 , pivotally suspended between brackets  68 ,  70  above support plate  12 , is pivotally actuated according to the teachings of the invention. 
     The base mast section  16  is a square, four sided elongate arm, having four sides  40 , a pair of through apertures  82  (one of which shown in FIG.  2 ), and a central, axial through passage  110 . The base mast passage  110  is intended to receive and support therein the second drive motor  18  shown in FIG.  2  and in greater detail in FIG.  7 . 
     Referring to FIG. 7, the second drive motor  18  is an in line ball drive actuator, of a type available in the industry. By way of example, without intending to limit the scope of the invention, a suitable ball actuator is manufactured and sold by Motion Systems Corporation located at 600 Industrial Way West, Eatontown, N.J. 07724 under part number 85258. The ball actuator comprises a motor housing  86  and a gear box housing  87 , a pair of outwardly extending lugs  85 , and a ball drive screw  90 . The screw  90  includes a geared epicyclic ball (not shown) at an inboard end across which gear teeth are spaced. A tubular cover  88  encases the ball drive screw  90  forward to a forward rod end eyelet  92 . 
     The stroke of the screw  90  is selected to correspond with the requisite distance between full “in” and full “out” positions of mast section  20 , as will be appreciated from FIGS. 1 and 3. The stroke length in the subject application is selected as thirty-two inches, however, an alternative stroke length may be utilized if desired. The ball drive actuator  18  is designed to provide high stroke speeds under relatively low loading as compared with the first ball actuator  14  described previously. The unit provides for direct coupling of the ball screw  90  to a motor (not shown) encased within housing  86 . The basic construction of the ball actuator  90  incorporates a high efficiency 0.653 inch diameter epicyclic ball screw with integral freewheeling at stroke ends to eliminate the need for limit switches. 
     The actuator  18  transmits thrust with the epicyclic ball screw  90 . Stop pins are provided (not shown) at each end of travel to initiate freewheel and linear advancement stops at those points. The epicyclic ball screw  90  thus moves along a reciprocal linear path to push and pull against the telescopic mast section  20  as will be explained below. 
     A standard 1:1 gear ratio is preferred in the ball drive actuator. The motor of actuator  18  is electrically powered in the preferred embodiment. For vehicle usage, the motor can be 12VDC; however for other applications an AC configuration may be preferable at the option of the user. 
     The cover  88  is fabricated from aluminum with a ring seal at its outboard end in order to protect the screw  90 . The rod end  92  is self-aligning and a weatherproof motor enclosure is provided to protect the motor from the elements. 
     The housing  87  is provided with external diametrically opposite lugs  85  used in mounting the motor  18  within the base mast section  16  as explained below. 
     Enclosing a top of the extendible mast section  20  is a server plate  98  having a central through aperture  100 . The plate  98  further has a pair of spaced apart sockets  104  in each of two opposite sides, providing attachments in affixing the plate to the mast section  20  by four screws  102 . The cover  98  fits over the top of the mast section  20  and provides a mounting surface for the lamp assembly  22 . 
     Mounted to the support plate  98  is a pivoting lamp fixture  22  and a pair of diametrically opposite lamps  24 ,  26 . The assembly comprising fixture  22 ,  24 ,  26  is commercially available. For example Havis Shields Corporation, located 395 Jacksonville Road, Warminster, Pa. 18974, manufactures and sells such devices as Model KR-31-37 light-heads. The Havis Shields units are available in both DC or AC versions. The assembly fixture pivots 360 degrees. The lamps  24 ,  26  are rotatably connected to fixture  22  and can rotate ninety degrees upward and forty degrees downward from the horizontal. The lamp assembly is powered by an electric motor housed within fixture  22 . While the assembly shown in the preferred embodiment is a lighting device, the subject invention is not intended to be so limited. Other applications will be apparent for the use of the telescoping mast assembly comprising the invention. By way of example, photographic, communication, or testing devices can be mounted to the upper end of the extendible mast  20  if so desired. 
     As best shown in FIGS. 1 and 2, a wiring harness  106  comprising a bundle of conductors  108  supplies electrical power and control signals to the motors  14 ,  18 , and to the lamp assembly  22 . The ball drive actuator  18  is mounted within a central passageway  110  of the base mast section  16  as lug projections  96  project through the apertures  82  and are fixedly retained by screws  84 . The extendible mast section  20  is telescopically received within the passageway  110  and an axial passageway  116  of section  20  is in coaxial alignment with the passageway  110 . The ball screw  90  projects upward into passageway  116  and is secured to extendible mast section  20  by a pin member  114  positioned through the ball screw eyelet  92  and an upper end portion of the mast section  20 . The stroke of ball screw  90  is selected such that the extendible mast section  20  will not escape the base mast section with the screw  90  in its full out position. 
     The first drive motor  14  is mounted fixedly to the base plate  12  as described above. So positioned, the ball screw  40  projects forward and is attached between the arms  63  of the base section support  58  by means of pin  65 . The motor  14  acts in reciprocal fashion to push the base mast section into a “down”, horizontal position when ball screw  40  is fully extended, and pull the base mast section  16  into an “up”, vertical, position when ball screw  40  is fully retracted. The ball screw  40  is positioned relative to the base mast section  16  so as to place the section  16  in the “up” and “down” positions at the opposite limits of the ball screw stroke. FIG. 3 illustrates movement of the base mast assembly between the “up” and “down” positions. 
     The operation of the ball drive actuator  14  is such that the base mast section  16  can be pushed or pulled to any position between the “up” and “down” positions and held in place. This affords the user maximum flexibility in avoiding obstructions and placing the lamp assembly in its optimal location. The base mast section  16  pivots with the support  58  and its position is positively controlled by the operator through electrical control of ball drive actuator  14 . Once positioned, the base mast section  16  remains in place until further movement is initiated by the ball drive actuator under control of the user. 
     Similarly, the operation of ball drive actuator  18  is such that the extendible mast section  20  can be pushed or pulled to any position between the fully extended, “out”, position and the fully retracted, “in”, position. This gives the user further control over positionment of the lamp assembly and allows the placement of the lamp assembly in an optimum location. Operation of motor  18  is independent of operation of motor  14  and electrical control signals can selectively transmitted to either or both motors  14 ,  18  to precisely place the mast section  20  or the base mast section  16  in its optimal position. Other pneumatic or hydraulic systems, which only function with the mast sections in either a fully retracted or fully extended position, limit the range of adjustment and substantially reduce the utility of the unit. 
     The positive operation of the motors  14 ,  18  upon respective mast sections  16 ,  20  supplies direct power to push or pull such masts in both extension and retraction directions. The motors thus can overcome radial ice build up between the telescoping mast sections in both the extension and retraction directions. Should ice build up while the mast sections are extended, the motors  14 ,  18  can overcome the resistance created thereby. In contrast, pneumatic systems use pneumatic power to extend the mast sections but rely upon gravity for retraction of the mast sections. Radial ice build up or ice at the mast junctions, or other contamination between the mast sections, may present such resistance that gravity will fail to bring the mast sections down. 
     A further advantage of the direct drive provided by the drive motor  18  is that actuation is along the axis of the extendible mast section. Mechanical advantage is thereby maximized. Moreover, the unit of the subject invention can effectively operate on slopes of twenty degrees or more because flexure at the junction of the mast sections will not impair the operation of motor  18 . In contrast, pneumatic units of the prior art which rely upon the maintenance of an air tight seal between mast sections will not work consistently over a fifteen degree slope. A greater slope will cause the tubes or mast sections of pneumatic systems to bend, causing air leaks to occur at the mast section junction and a corresponding failure in the drive system. 
     It will further be appreciated that the subject telescoping mast assembly is sealed from the elements and, accordingly, will function more dependably than alternative prior art systems. The ball drive actuators are sealed against intrusion of water or contaminants. Secondly, the axial passageways in which the actuators reside are enclosed. The cover plate  98  at the top prevents intrusion of the elements from above. Moreover, the base section support  58 , base mast section  16 , and extendible mast section  20  are enclosed in the assembled condition, preventing the majority of the elements from reaching the ball drive actuators. Prior art devices, for example hydraulic units, have operative components exposed to the elements and can fail from such exposure. 
     The subject assembly as described above comprises a relatively small number of component parts which are readily assembled and which can, if necessary, be readily repaired. The ball drive actuators  14 ,  18  can be easily disconnected from their respective mast sections and removed. Replacement of the actuators is equally convenient and can be accomplished with minimal down time. In contrast, hydraulic, pneumatic, or hybrid systems are complicated, comprise a relatively large number of parts, and are relatively more difficult to assemble and repair. In addition, as explained previously, such alternative systems have components mounted in an exposed manner and such components are frequently damaged from rough handling or dirt contamination. The subject invention protects the drive motors within the shaft sections and avoids contact with external obstructions. 
     From FIGS. 1 and 2 it will be noted that the wiring cable  106  enters into the passageway  110  of the base mast section  16  via aperture  61  and thence proceeds upward through the wiring harness for the subject telescoping mast assembly is housed within the mast sections from the base of the assembly to any device mounted to the top. The wiring is accordingly protected and will not snag or contact obstructions which are inevitably present in field applications. In contrast, prior art mast assemblies have external wiring which can snag on maintenance tools, or low branches or overhead obstructions. Damage to the wiring may remain undetected until the unit is needed in an emergency situation, creating a hazard to those relying upon the unit to function as intended. 
     Referring to FIG. 1, it will be appreciated that the uppermost mast section  20  can be formed of steel plating if desired. However, according to the teachings of the invention, it is desirable to form the uppermost section  20  from a non-conductive material such as plastic or fiber glass. In so doing, the transfer of an electrical charge from the device at the top of the mast or from the uppermost mast section down to the vehicle that the unit is mounted upon will be prevented. This is critical in an emergency situation where lights, cameras, or other devices mounted on top of the pop-up telescoping mast system can inadvertently be placed into unguarded electrical wires. Furthermore, since the wiring harness  106  is encased within and protected by the mast sections, a fuse system  116  can be incorporated into the wiring circuit within the protected mast passageways and ameliorate concern that the fuse may prove inoperative due to exposure to the elements over time. A fuse  116 , of the type common in the industry, in the protected environment of the enclosed mast sections of the present invention will be free of failure from exposure to the elements and will function as expected to stop a surge of electric current from the wires going into the base of the unit, and therefrom into the vehicle frame. A suitable fuse system is manufactured by McMaster-Carr Supply Co. located at 200 Aurora Industrial Parkway, Aurora, Ohio 44202, as parts numbers 7085K78 and 7696K31. 
     In addition to the advantages summarized above, the subject invention provides a lightweight alternative to conventional telescoping mast systems. The component configuration of the telescoping mast system of the invention, namely the two mast sections, mounting plate, and dual ball drive actuators, is significantly lighter than hydraulic or pneumatic alternatives. This weight reduction not only makes the subject unit easier and more convenient to install, but also reduces the stress imposed upon the vehicle roof to which the unit is attached. 
     An alternative three section telescoping mast assembly is depicted in FIG.  8 . Shown in phantom are two ball actuator drives  18 - a ,  18 - b  used to extend and retract respective extendible mast sections  20 - a ,  20 - b . The addition of a mast section  20 - b  allows for extended reach while still affording the same reliability and adjustability advantages of the two mast section described previously. It will be appreciated that, as with the preferred embodiment, the three section alternative embodiment employs a ball drive actuator for each of the mast sections. A high load actuator  14  is mounted on the base plate  12  as described previously and pivots the base mast section  16  and extendible mast sections  20 - a  and  20 - b  between a horizontal “down” position and a vertical “up” position. The motors and the wiring harnesses are encased within the mast sections and are protected from the elements and from contact with obstructions. 
     While the above describes a preferred and an alternative embodiment of the subject invention, the invention is not intended to be so restricted. Other embodiments, which will be apparent to those skilled in the art and which utilize the teachings herein set forth, are intended to be within the scope and spirit of the invention.