Abstract:
A light-emitting device and a related projection system. Light-emitting devices ( 300, 400 ) comprise: a light source unit ( 1 ) and focusing lenses ( 330, 430 ). The light source unit ( 1 ) comprises laser units ( 310, 410 ) and collimating lenses ( 320, 420 ) corresponding to the laser units ( 310, 410 ). The light-emitting surface of the laser units ( 310, 410 ) is a rectangle, and the light divergence angle of laser passing through the cross-section of the long side of the rectangle is smaller than the light divergence angle of same passing through the cross-section of the short side of the rectangle. The collimating lenses ( 320, 420 ) are used for focusing the laser from the laser units ( 310, 410 ) on a target surface to form a predetermined light spot. The laser units ( 310,   410 ) are located on the light axis of the collimating lenses ( 320, 420 ) in a predetermined position deviating from the focal point thereof, so that the predetermined light spot has a predetermined length-width ratio. The light-emitting device and the related projection system have the advantages of relatively small regulation quantity and relatively high assembly efficiency.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to illumination and display technologies, and in particular, it relates to a light-emitting device and related projection system. 
         [0003]    2. Description of the Related Art 
         [0004]    Because lasers have the advantages of high brightness and high color purity, they have been widely used in illumination and display technology areas in recent years. 
         [0005]    The light distribution of a laser beam is typically an elliptical Gaussian distribution, and the ratio of the major axis to the minor axis is typically large, such as 10:1. In some practical applications, however, the light spot of a light source are required to be a rectangle of a specific aspect ratio. For example, in display technologies, the display screens typically have an aspect ratio of 4:3 or 16:9. Thus, laser beams cannot be directly used as the display light source; light beams from multiple lasers have to be combined using lenses so that the light spots from the multiple lasers are fit together to form a light spot of an aspect ratio of 4:3 or 16:9. 
         [0006]    For example, refer to  FIGS. 1   a  and  1   b , where  FIG. 1   a  is a plan view of a conventional light source for a projection system, and  FIG. 1   b  illustrates the light spots on the phosphor material in  FIG. 1   a . As shown in  FIGS. 1   a  and  1   b , the conventional light source for the projection system includes multiple laser units  11 , multiple collimating lenses  12 , a focusing lens  13 , a phosphor material  14 , a base plate  15 , and a motor  16 . The base plate  15  is affixed to and driven by the motor. The phosphor material  14  has a ring shape coaxial with the base plate  15  and is disposed directly in contact with it. The laser beams emitted by the laser units  11  are collimated by the corresponding collimating lenses  12  onto the focusing lens  13 , and focused by the focusing lens  13  onto the phosphor material  14  to excite the phosphor material  14 . The multiple laser units are divided into eight groups, the light spots of all laser units within each group overlap with each other on the phosphor material  14 . The laser beams emitted by the eight groups of laser units form eight non-overlapping light spots  17   a,  which collectively form a predetermined light spot in the rectangular area  17  on the phosphor material  14  (the target plane). 
         [0007]    Because multiple light spots are required to be combined to form the predetermined light spot, for each group of laser units, at least one of each laser units  11  and their corresponding collimating lenses  12  need to be adjusted during assembly, to ensure that the light spot formed by each group of laser units  11  on the phosphor material is located at the corresponding predetermined position. This affects the efficiency of assembly and increases assembly cost. 
       SUMMARY OF THE INVENTION 
       [0008]    An object of the present invention is to provide a light source device and related projection system that at least requires less adjustment and hence has higher assembly efficiency. 
         [0009]    An embodiment of the present invention provides an illumination device having a light emitting device, which includes at least one light source unit, the light source unit including a laser unit and a collimating lens corresponding to the laser unit, wherein a light emitting surface of the laser unit is a rectangle, wherein a divergence angle of a laser light emitted by the laser unit in a cross-section that goes through a long side of the rectangle is less than a divergence angle of the laser light in a cross-section that goes through a short side of the rectangle; and a focusing lens, wherein the collimating lens collimates the laser light emitted by the laser unit onto the focusing lens, and the focusing lens focuses the laser light from the collimating lens onto a target plane to form a predetermined light spot, wherein the laser unit is located on an optical axis of the collimating lens at a position away from a focal point of the collimating lens, wherein the predetermined light spot has a predetermined aspect ratio. 
         [0010]    The light emitting device may include a group of light source units, the group including a plurality of light source units; wherein the focusing lens focuses the laser light emitted by the plurality of light source units of the group to a common position on the target plane to form the predetermined light spot. 
         [0011]    The light emitting device may include two groups of light source units, each group including a plurality of light source units, wherein the focusing lens focuses the laser light emitted by the plurality of light source units of each of the two groups to a common position on the target plane to respectively form two individual light spots, and wherein the two individual light spots collectively form the predetermined light spot. 
         [0012]    The light emitting device may further include a light combination device that has transmitting parts and reflecting parts, wherein the laser light emitted by the first one of the two groups of light source units passes through the light transmitting parts to reach the focusing lens, and the laser light emitted by a second one of the two groups of light source units is reflected by the light reflecting parts to reach the focusing lens. 
         [0013]    The light combination device may be a reflecting minor having slits or a transmitting plate having reflective strips. 
         [0014]    The light emitting device may further include an angle adjusting mechanism for adjusting the light combination device to change an incident angle of the laser light emitted by the second one of the two groups of light source units onto the reflecting parts of the light combination device. 
         [0015]    In the light emitting device, a distance between the laser unit and the corresponding collimating lens is less than a focal distance of the corresponding collimating lens. 
         [0016]    The light emitting device may further include a position adjusting mechanism, for moving the collimating lens linearly along its optical axis. 
         [0017]    The light emitting device may further include a wavelength conversion layer, wherein the target plane is located at the wavelength conversion material. 
         [0018]    Embodiments of the present invention also provide projection system which includes the above light emitting device. 
         [0019]    Compared to conventional technologies, embodiments of the present invention have the following advantages: 
         [0020]    By placing the laser unit at a position away from the focal point of the collimating lens, the laser beam forms a predetermined light spot of predetermined aspect ratio on the target plane. Thus, when a single predetermined light spot fills the entire predetermined rectangular area, only a single group of laser units or even only a single laser unit can be used to form the predetermine light spot; it is not necessary to use multiple groups of light source units to form multiple non-overlapping light spots. Thus, the step of adjusting the groups of laser units in conventional technology can be omitted. Even when the light spot formed by one group of laser units cannot fill the entire rectangular area, because the light spot size is larger when the laser unit is off-focus as compared to when it is located at the focal point, embodiments of the present invention still has the advantage that fewer non-overlapping light spots are required to fill the entire rectangular area, and therefore fewer groups of laser units are required as compared to conventional technology. Therefore, less adjustment of the groups of laser units or collimating lenses is required. It can be seen that embodiments of the present invention have the advantage of less adjustment and higher assembly efficiency. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0021]      FIG. 1   a  is a plan view of a conventional light source for a projection system; 
           [0022]      FIG. 1   b  illustrates the light spots on the phosphor material in  FIG. 1   a;    
           [0023]      FIG. 2   a  illustrates a structure when the laser unit is located at the focal point of the collimating lens and when it is located away from the focal point; 
           [0024]      FIG. 2   b  illustrates the light beam emitted by the laser unit of  FIG. 2   a;    
           [0025]      FIG. 3   a  is a plan view of a light emitting device according to an embodiment of the present invention; 
           [0026]      FIG. 3   b  illustrates the light spot formed on the target plane in the embodiment of  FIG. 3   a;    
           [0027]      FIG. 4   a  is a plan view of a light emitting device according to another embodiment of the present invention; 
           [0028]      FIG. 4   b  illustrates the light spot formed on the target plane in the embodiment of  FIG. 4   a;    
           [0029]      FIG. 5   a  is a plan view of a light emitting device according to another embodiment of the present invention; and 
           [0030]      FIG. 5   b  is a left-side view of the light combination device of the embodiment of  FIG. 5   a.    
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    For clarity, technical terms used in this disclosure and the figures are defined below: 
         [0032]    Aspect ratio: The ratio of the major axis to the minor axis of an ellipse, or the length to width ratio of a rectangle. 
         [0033]    It is generally believed by those in the relevant technical field that, regardless of whether a laser unit is placed at the focal point of the collimating lens or placed on the optical axis of the collimating lens but away from the focal point, the laser light emitted by the laser unit will form a light spot on the target plane that has a shape similar to that of the light emitting surface of the laser unit. 
         [0034]    However, the inventors of the present invention discovered through experimentation that, when some laser units are placed on the optical axis of the collimating lens but away from the focal point, the shape of the light spot formed on the target plane by the laser light emitted from the laser unit is dissimilar to the shape of the light spot formed when the laser unit is located at the focal point. Refer to  FIG. 2   a , which shows the structure of the laser unit being located at the focal point of the collimating lens and away from the focal point, as well as the corresponding elliptical light spots formed on the target plane. 
         [0035]    As shown in  FIG. 2   a , when the laser unit  210  is exactly located at the focal point of the collimating lens  220 , i.e. when the collimating lens  220  is at position A along the optical axis, the light spot formed on the target plane by the collimating lens  220  and after passing through a focusing lens (not shown) is a thin and long ellipse a. When the laser unit  210  is located on the optical axis of the collimating lens  220  but away from the focal point, e.g. when the collimating lens  220  is at position B which is closer to the laser unit  210  than position A, the light spot formed on the target plane by the collimating lens  220  and after passing through the focusing lens is an ellipse b, where the aspect ratio of light spot b is smaller than that of the light spot a. When the laser unit  210  is located at position A which is even closer to the laser unit  210  than position B, the light spot formed on the target plane by the collimating lens  220  and after passing through the focusing lens is an ellipse c, where the aspect ratio of light spot c is smaller than that of the light spot b. Moreover, the light spot c almost fills the entire predetermined rectangular area  270  on the target plane. 
         [0036]    Empirical studies by the inventors reveal that, some types of laser units have the effect that when the laser unit is located on the optical axis of the collimating lens but away from the focal point (referred to as “off-focus” hereinafter), the elliptical light spots formed on the target plane will have different aspect ratios, and such laser units typically have the following characteristics: The light emitting surface of the laser unit is rectangular, and the divergence angle of the emitted light beam in a cross-section that goes through the long side of the rectangle is less than the divergence angle in a cross-section that goes through the short side of the rectangle. The inventors&#39; theoretical analysis of this empirical result reveals that the reasons that such laser units can form elliptical light spots of different aspect ratios on the target plane are as follows: As shown in  FIG. 2   b , the light emitting surface of the laser unit  210  is rectangular, its divergence angle in a cross-section that goes through the long side  211  of the rectangle is α, and its divergence angle in a cross-section that goes through the short side  212  of the rectangle is β. Because α is smaller than β, when the laser unit is placed off-focus, the major axis  213  of the laser beam distribution increases faster than the minor axis  214 , causing the minor axis of the elliptical light spot on the target plane (not shown) to increase faster than the major axis of the light spot, which changes the aspect ratio of the elliptical light spot. 
         [0037]    It can be seen that, by placing the laser unit on the optical axis of the collimating lens at a position away from the focal point, the aspect ratio of the elliptical light spot formed on the target plane can be changed, thereby achieving a desired aspect ratio. Based on this discovery, the inventors invented a light emitting device, which includes: 
         [0038]    A light source unit, which includes a laser unit and a collimating lens corresponding to the laser unit. The light-emitting surface of the laser unit is a rectangle, and the divergence angle of the emitted laser light in a cross-section that goes through the long side of the rectangle is less than the divergence angle in a cross-section that goes through the short side of the rectangle. The collimating lens collimates the laser light emitted by the laser unit onto a focusing lens. 
         [0039]    A focusing lens, for focusing the laser light from the collimating lens onto a target plane to form a predetermined light spot. 
         [0040]    The laser unit is located on the optical axis of the corresponding collimating lens at a position away from the focal point of the collimating lens, such that the predetermined light spot has a predetermined aspect ratio. 
         [0041]    Compared to conventional technologies, embodiments of the present invention place the laser unit at a position away from the focal point of the collimating lens, so that the laser beam forms a predetermined light spot of predetermined aspect ratio on the target plane. Thus, when a single predetermined light spot fills the entire predetermined rectangular area, only a single group of laser units or even only a single laser unit can be used to form the predetermine light spot; it is not necessary to use multiple groups of light source units to form multiple non-overlapping light spots. Thus, the step of adjusting the groups of laser units in conventional technology can be omitted. Even when the light spot formed by one group of laser units cannot fill the entire rectangular area, because the light spot size is larger when the laser unit is off-focus as compared to when it is located at the focal point, embodiments of the present invention still has the advantage that fewer non-overlapping light spots are required to fill the entire rectangular area, and therefore fewer groups of laser units are required as compared to conventional technology. Therefore, less adjustment of the groups of laser units or collimating lenses is required. It can be seen that embodiments of the present invention have the advantage of less adjustment and higher assembly efficiency. 
         [0042]    Embodiments of the present invention are described below in more detail with reference to the drawings. 
       First Embodiment 
       [0043]    Refer to  FIGS. 3   a  and  3   b , where  FIG. 3   a  is a plan view of a light emitting device according to an embodiment of the present invention, and  FIG. 3   b  illustrates the light spot formed on the target plane in the embodiment of  FIG. 3   a . As shown in  FIG. 3   a , the light emitting device  300  includes light source units  1 , a focusing lens  330 , and a wavelength conversion layer  340 . Each light source unit  1  includes a laser unit  310  and a collimating lens  320  corresponding to the laser unit. 
         [0044]    The laser units  310  may be any type of laser units that generate light of any color. For example, the laser units  310  may be laser diodes that generate blue, green or red light. 
         [0045]    Each laser unit  310  has a corresponding collimating lens  320 , for collimating the light from the laser unit  310  to the focusing lens  330 . The collimating lens  320  is preferably an aspherical collimating lens, which has superior collimating properties. The collimating lens  320  may also be a spherical collimating lens of free-curve-surface collimating lens. 
         [0046]    In this embodiment, the light emitting device  300  includes one light source unit group which includes multiple light source units  1 . Also, the target plane is located on the wavelength conversion material layer  340 . The focusing lens  330  focuses the laser beams from all of the multiple light source units  1  to the same light spot position on the target plane to form the predetermined light spot  370   a;  in other words, the laser light emitted by all of the multiple light source units in a group are superimposed on the target plane to form the predetermined light spot  370   a.  The predetermined light spot  370   a  almost fills the entire predetermined rectangular area  370 , and its aspect ratio is approximately equal to the aspect ratio of the rectangular area. 
         [0047]    In this embodiment, the rectangular area  370  is the same as the rectangular area  17  in  FIG. 1   b , and the configurations of the various optical components are also similar to those of  FIG. 1   a . Assuming that the aspect ratio of each single light spot in  FIG. 1   b  is a:b, and the ratio of the length of the rectangular area  17  to the length of each single light spot is 1.5; then in the instant embodiment, by placing the laser units off-focus, each single light spot fills the entire rectangular area  370 . From  FIG. 1   b  and  FIG. 3   b  together, it can be seen that the aspect ratio of the single light spot in this embodiment is (1.5a)/(6b)=a/(4b). Thus, it can be seen that in this embodiment, by placing the laser units off-focus, the aspect ratio of the single light spots is reduced by 4 times. 
         [0048]    In this embodiment, because the individual light spot formed by each light source unit  1  fills the entire predetermined rectangular area, only a single group of laser units or even only a single laser unit can be used to form the predetermine light spot  370   a;  it is not necessary to use multiple groups to form multiple non-overlapping light spots. Thus, the step of adjusting each group of laser units in the conventional technology can be omitted and higher assembly efficiency is achieved. 
         [0049]    Preferably, the light source units  1  of each group of light source units are the same; after the distance between the laser units  310  and corresponding collimating lenses  320  is calculated based on the aspect ratio of the predetermined light spot, all light source units  1  of the group can be mounted on a common base to form a light source module. Thereafter, only the light source module and the focusing lens  330  need to be adjusted, significantly reducing assembly cost. 
         [0050]    In this embodiment, the laser units  310  emit a blue light. The wavelength conversion material layer  340  is a phosphor material, such as YAG phosphor, which absorbs the blue excitation light and emits a yellow converted light. The wavelength conversion material layer  340  may also use other wavelength conversion materials, such as quantum dots, fluorescent dye, etc., in addition to phosphors. Often, phosphor materials are a powder or particulate form and it is difficult to form a layer by themselves. Thus, an adhesive may be used to adhere the phosphor powder or particles together to form a plate. A commonly used method is to disperse phosphor powder in an adhesive material, and use the adhesive material as a carrier to carry the phosphor powder and form a plate. 
         [0051]    Because phosphor layers are often brittle and fragile, preferably, the light emitting device  300  additionally includes a base plate  350  for carrying the wavelength conversion material layer  340 . Specifically, the wavelength conversion material layer  340  may be glued to or coated onto the base plate  350 . Of course, when the wavelength conversion material layer has sufficient mechanical strength, for example when the wavelength conversion material layer is formed by mixing a phosphor powder in a transparent glass which has sufficient mechanical strength, the base plate can be omitted. 
         [0052]    Further, the base plate  350  is a round plate, and the wavelength conversion material layer  340  is a ring shape concentric with the base plate  350 . The light emitting device  300  further includes a drive device  360 , fixedly connected to the base plate  350 , to drive the base plate  350  to rotate around its axis, so that the light spot formed by the laser beam from the focusing lens  330  illuminates the wavelength conversion material layer  340  along a predetermined circular path. This prevents the problem of temperature rise of the phosphor material caused by the laser light illuminating the same position of the phosphor material for extended periods of time. It should be understood that the drive device  360  and the wavelength conversion material layer  340  can be mechanically coupled in other ways, so long as the light spot formed by the laser beam from the focusing lens  330  illuminates different parts of the phosphor material at different times. For example, the wavelength conversion material layer can be a strip shape and the drive device  360  can drive the base plate to oscillate linearly along the direction of the strip. 
       Second Embodiment 
       [0053]    The light emitting device may also include two groups of light source units, forming two non-overlapping light spots on the target plane, which are combined to form the predetermined light sport. Specifically, refer to  FIGS. 4   a  and  4   b , where  FIG. 4   a  is a plan view of a light emitting device according to the second embodiment of the present invention and  FIG. 4   b  illustrates the light spot formed on the target plane in the embodiment of  FIG. 4   a . As shown in  FIG. 4   a , the light emitting device  400  includes light source units  1 , a focusing lens  430 , a wavelength conversion layer  440 , a base plate  450  and a drive device  460 . Each light source unit  1  includes a laser unit  410  and a collimating lens  420  corresponding to the laser unit. 
         [0054]    Differences between this embodiment and the embodiment of  FIG. 3   a  include: 
         [0055]    The light emitting device  400  includes two groups of light source units, each group including multiple light source units  1 . Further, the focusing lens  430  focuses the light beams from the multiple light source units within the same group to a common light spot position on the target plane, and focuses the light beams from the two groups of light source units respectively to two light spot positions  470   a  and  470   b.  The two light spots  470   a  and  470   b  are combined to form the predetermined light spot, which almost fills the entire predetermined rectangular area  470 . The aspect ratio of the predetermined light spot is approximately equal to the aspect ratio of the predetermined rectangular area. 
         [0056]    In this embodiment, although the light spot formed by one group of light source units cannot fill the entire rectangular area, because the light spot size when the laser units are off-focus is larger than that when the laser units are located at the focal point of the collimating lenses, this embodiment requires fewer light spots to fill the entire rectangular area and therefore fewer groups of laser units as compared to the conventional technology. Thus, the amount of required adjustment of the laser units or collimating lenses in the groups of light source units is reduced. 
         [0057]    Further, as shown in  FIG. 4   b , the two light spots formed by the two groups of light source units on the target plane have the same shape and size, and they overlap partially in their edge areas. Because the light intensity in the edge areas of the light spots is lower than in the center areas, the partial overlap of the two light spots in the edge areas improves the intensity uniformity of the combined predetermined light spot. 
         [0058]    Because two light spots formed by the two groups of light source units have the same shape and size, the configurations of the two groups of light source units can be the same, and the light source units of the two groups can be respectively mounted on two bases to form two identical light source modules. Thereafter, only the angles of the bases of the two light source modules relative to the focusing lens need to be adjusted to achieve the result that the two light spots generated by the two groups of light source units are located at the two different predetermined positions on the target plane. 
       Third Embodiment 
       [0059]    To more conveniently adjust the two groups of light source units in the embodiment of  FIGS. 4   a  and  4   b , the light emitting device may additionally include a light combination device that has transmitting parts and reflecting parts. Of the two groups of light source units, the laser beams outputted by the first group passes through the light transmitting parts to reach the focusing lens, and the laser beams outputted by the second group is reflected by the light reflecting parts to reach the focusing lens, so as to be combined with the output light of the first group into one beam. By simply adjusting the angle between the light combination device and the focusing lens, the angle of the laser light reflected by the reflecting parts can be adjusted, which changes the relative positions of the light spots on the target plane formed by the reflected laser light and the transmitted laser light. 
         [0060]    More specifically, refer to  FIGS. 5   a  and  5   b , where  FIG. 5   a  is a plan view of a light emitting device according to the third embodiment of the present invention, and  FIG. 5   b  is a left-side view of the light combination device of the embodiment of  FIG. 5   a . As shown in  FIG. 5   a , the light emitting device  500  includes light source units  1 , a focusing lens  530 , a wavelength conversion material layer  540 , a base plate  550  and a drive device  560 . 
         [0061]    Differences between this embodiment and the embodiment of  FIG. 4   a  include: 
         [0062]    The light emitting device  500  additionally includes a light combination device  580 . As shown in  FIG. 5   b , the light combination device  580  is a reflecting minor having slits  581 . Of the two groups of light source units, the laser light emitted by the first group passes through the slits  581  to reach the focusing lens  530 , and the laser light emitted by the second group is reflected by the areas of the reflecting mirror other than the slits  581  to reach the focusing lens  530 , so that the laser light emitted by the two groups of light source units are combined into one beam. As discussed above, by simply adjusting the angle of the reflecting mirror  580  relative to the focusing lens  530 , the combination of the two light spots can be adjusted to form the predetermined light spot. Moreover, by using the reflecting minor  580  to combine the laser light from the two groups of light source units, the light spot formed by the combined light from the two groups can be compressed. 
         [0063]    It should be understood that, in other embodiments, the light combination device may be a light transmitting plate having reflective strips. In such a case, of the two groups of light source units, the laser light from the first group is reflected by the reflective strips to reach the focusing lens, and the laser light from the second group is transmitted through the areas of the transmitting plate other than the strips to reach the focusing lens. 
         [0064]    Further, the light emitting device may also include an angle adjusting mechanism, to adjust the light combination device in order to change the incident angle of the laser light from the second group of light source units onto the reflecting parts of the light combination device. For example, the angle adjusting mechanism may rotate the reflecting minor  580  to change the incident angle of the laser light incident on the reflecting parts of the reflecting mirror  580 . This allows adjustment of the combined light spot formed on the target plane by the two light spots based on the user&#39;s needs. 
         [0065]    In these embodiments, the detailed mechanism of how to place the laser units away from the focal point of the collimating lens is explained below. Preferably, the collimating lens is moved toward the laser unit from the ideal collimating position (i.e. the position where the laser unit is located at the focal point of the collimating lens), i.e., the distance between the laser unit and the corresponding collimating lens is less than the focal distance of the collimating lens. At this position, the light collecting angle of the collimating lens is larger, so the light utilization efficiency is higher. The distance of the laser unit from the focal point should not be too large; 
         [0066]    preferably, the difference between the off-focus collimating lens position and the ideal collimating lens position is less than 0.5 mm. 
         [0067]    Further, the light emitting device may include a position adjusting mechanism, which can move the collimating lens linearly along its optical axis, to adjust the aspect ratio of the light spot formed by laser light of the laser unit on the target plane based on the user&#39;s needs. 
         [0068]    In this disclosure, the various embodiments are described progressively, where later embodiments are described by emphasizing its differences form earlier embodiments. For similarities among the various embodiment, the embodiments can refer to each other. 
         [0069]    Another embodiment of the present invention is a projection system, which includes a light emitting device having structures and functions of the above-described embodiments. The projection system can employ various projection technologies, such as LCD (liquid crystal display) projection technology, DLP (digital light processor) projection technology, etc. Further, the above-described light emitting devices may be used in illumination systems such as stage lighting. 
         [0070]    It will be apparent to those skilled in the art that various modification and variations can be made in the apparatus and method of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover modifications and variations that come within the scope of the appended claims and their equivalents.