Patent Publication Number: US-2022227167-A1

Title: Variable Compliance Wheel

Description:
RELATED APPLICATIONS 
     This application is a continuation of and claims priority to U.S. patent application Ser. No. 16/503,361 filed Jul. 3, 2019 entitled Variable Compliance Wheel, which is a continuation of and claims priority to U.S. patent application Ser. No. 15/817,033 filed Nov. 17, 2017 entitled Variable Compliance Wheel (now abandoned), which is a continuation of and claims priority to U.S. patent application Ser. No. 14/135,410 filed Dec. 19, 2013 entitled Variable Compliance Wheel (now abandoned), which is a divisional of and claims priority to U.S. patent application Ser. No. 11/574,810 filed Mar. 6, 2007 entitled Variable Compliance Wheel (now U.S. Pat. No. 8,631,844 issued Jan. 21, 2014), which is a continuation-in-part of and claims priority to International Patent Application No. PCT/US2005/015478, International Filing Date Jun. 13, 2005, entitled Variable Radial And/Or Lateral Compliance Wheel and which claims priority to U.S. Provisional Application Ser. No. 60/869,714 filed Dec. 12, 2006 entitled Variable Compliance Wheel (now expired), all of which are hereby incorporated by reference in their entireties. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention generally relates to a wheel with variable compliance having many applications, including ground vehicle wheels, printing press rollers, material processing and handling equipment. More particularly, the present invention relates to a wheel that includes a rim having a center axis of rotation and a plurality of wheel segments engaged with the rim and connecting to a radial band appropriate for the intended usage of the wheel, where the rim and plurality of wheel segments are adapted to rotate about the center axis, and where the attachment points to the rim of the plurality of wheel segments can be moved in the direction of the axis of rotation. In the example of a ground vehicle application, the radial band includes tread elements to improve vehicle traction in wet or rough road surfaces or in complex terrain. For material handling applications, the radial band may have a smooth surface to apply even pressure to a printing medium, for example, or may contain striations or tread elements as required. 
     Various mechanisms currently exist for varying the ground contact pressure of a tire while a vehicle is being driven. This capability allows a vehicle to traverse soft soils by lowering the pressure within the tire, without compromising on-road performance. This is commonly achieved by varying the pressure within the carcass of a tire through the control of an air valve mounted on the wheel that can vent the tire&#39;s internal air to atmospheric pressure or to the pressure produced by an onboard air compressor plumbed through an airtight rotary seal. The commercial term for such a system is Central Tire Inflation System (CTIS). One such system is U.S. Pat. No. 5,553,647, “Central tire inflation system,” (Miroslav), the contents of which are hereby incorporated by reference, that describes a pressure air source, plumbing, valve, pressure sensor, and control system for varying the internal air pressure of a tire while driving. The shortcomings of this design are complexity, sensitivity to the elements, cost, and inability of the system to maintain adequate tire pressure when the tire is badly damaged. 
     Several patents have addressed this latter concern of pneumatic tire vulnerability with runflat inserts (U.S. Pat. No. 6,263,935, “Radial ply pneumatic runflat tire,” (Oare, et. al.)) or tires that do not rely on fluidic pressure for load carrying, a.k.a. non-pneumatic tires, (U.S. Pat. No. 6,431,235, “Non-pneumatic tire and rim combination,” (Steinke, et. al.)), the contents of both of these patents hereby incorporated by reference. The shortcomings of this system are weight and fixed tire stiffness. 
     The present invention describes a novel way of combining the benefits of variable tire stiffness with a damage tolerant tire design. 
     SUMMARY OF THE INVENTION 
     The present invention provides a variable stiffness wheel that can be used in a variety of applications, such as for support of ground vehicle traverse over a variety of terrain or for conveying materials (e.g., airport baggage handling). In one preferred embodiment, the variable stiffness wheel includes a plurality of wheel segments whose attachments to the center rotating rim (inner and outer) can be moved in the direction of the axis of rotation, thereby changing the tension of these elements, which is convenient, in one example, for tuning the ground contact pressure of the tire for the terrain being traversed. The inner attachment being accommodated via a sliding flange located towards the vehicle and the outer being accommodated via another sliding flange located away from the vehicle. Additionally, this method can be used to vary other wheel stiffness parameters such as vertical stiffness, lateral stiffness, torsional stiffness (about the axis of rotation or about an axis perpendicular to the axis of rotation) each of which can affect overall behavior of the system the wheel is used in (e.g., vehicle performance). 
     With the inner and outer wheel segment attachment points close together tensioning the spokes, the vertical stiffness of the wheel is increased. In the example of the vehicle wheel, this increased stiffness generally provides excellent on-road performance (cornering, steering feel, low rolling resistance, etc.) and increased payload carrying capacity and increased durability at high speeds. 
     With the inner and outer wheel segment attachment points spread apart from one another, the vertical stiffness of the wheel is reduced, enlarging the contact patch of the wheel with, for example, the ground, baggage, or other material. In the example of a printer, the stiffness of the print roller can be modulated to compensate for plate wear, extending the life of the plate and improving the throughput of the press. In the example of the vehicle wheel, the tire/terrain enveloping performance is improved, while the lower ground pressure gives the vehicle better off-road mobility on soft soils like mud, sand, and snow. 
     Continuing with the example of the vehicle, the inner and outer wheel segment attachment points spread far apart from one another which allows the vehicle to be lowered, thereby facilitating transportation in low clearance vehicles like aircraft. The lower ground pressure of this configuration is also beneficial to ramps and cargo floors that have strict limits on floor loading pressure due to floor structure limitations imposed by weight constraints, as is the case with many aircraft. 
     The inner and outer wheel segment attachment points can be varied from the maximum and minimum spacing while driving to suit the immediate needs of the vehicle. 
     Multiple inner and outer wheel segments can be stacked to produce a wheel with varying radial stiffness across the width of the wheel. This is beneficial for improving the lateral performance of the wheel by controlling the wheel&#39;s dynamic camber. In the example of wheels supporting a conveyer belt, this varying stiffness across the wheel width may help direct or steer baggage in a desired direction. In the example of a printer, the varying radial stiffness of a printer roller may direct paper in a desired direction or area, such as continuously adjusting the registration of multicolor press runs. This reduces the waste and rework associated with misregistered press output. 
     In the example of the vehicle, the dynamic camber can adjusted during cornering to improve maneuvering performance. This can also be beneficial for changing the heading of the vehicle while driving with little or no steering of the tire. By making the stiffness of the innermost pair of inner and outer wheel segments stiffer than the outermost pair, resulting forces at the wheel/road contact patch will serve to pull the vehicle in the direction of the outermost pair of wheel segments. Further, by reversing the relative stiffness between the two sections, the wheel can force the vehicle in the opposite direction. This has the potential of simplifying the steering system, reducing cost and weight, improving the durability of the suspension/steering system by eliminating vulnerable steering links, and reclaiming the swept volume lost to the tire as it steers for other vehicle components or cargo. Additionally, the radial wheel stiffness, when modulated at a high rate, can be used to counteract vehicle pitch and heave vibrations, augmenting or even replacing the vibration isolation functions of the vehicle&#39;s suspension system. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an isometric view of a preferred embodiment of a wheel of variable stiffness of the present invention; 
         FIG. 1B  is a side view of the variable stiffness wheel of  FIG. 1 ; 
         FIG. 2  is a detail isometric view of a cutaway of the variable stiffness wheel of  FIG. 1 , showing the movable elements of the wheel with a portion of the wheel removed; 
         FIG. 3  is a cross sectional view of the variable stiffness wheel of  FIG. 1 ; 
         FIG. 4  is a side view of a second preferred embodiment of a wheel of variable stiffness of the present invention; 
         FIG. 5A  is an isometric cutaway view of the variable stiffness wheel shown in  FIG. 4 ; 
         FIG. 5B  is an enlarged detail view of  FIG. 5A ; 
         FIG. 6  is a cross sectional view of the preferred embodiment of  FIGS. 5  A and B; 
         FIG. 7A  illustrates a speed-sensitive automatic stiffness adjustment mechanism according to a preferred embodiment of the present invention; 
         FIG. 7B  illustrates a speed-sensitive automatic stiffness adjustment mechanism according to a preferred embodiment of the present invention; 
         FIG. 8A  describes a pneumatic stiffness adjustment mechanism which can be employed with either preferred embodiment of a wheel of variable stiffness of the present invention; 
         FIG. 8B  describes a pneumatic stiffness adjustment mechanism which can be employed with either preferred embodiment of a wheel of variable stiffness of the present invention; 
         FIG. 9  illustrates a top view of a luggage carrier according to a preferred embodiment of the present invention; 
         FIG. 10A  is a front view of a variable stiffness wheel with a manually-operated stiffness adjustment mechanism according to a preferred embodiment of the present invention; 
         FIG. 10B  is a partial cross sectional view along line B of  FIG. 10A ; 
         FIG. 10C  is a partial cross sectional view along line C of  FIG. 10A ; 
         FIG. 11  is a partial cross sectional view along line A of  FIG. 10A ; 
         FIG. 12A  is an exploded isometric view of the wheel center and manually-operated stiffness adjustment mechanism of  FIG. 11 ; and 
         FIG. 12B  is an additional exploded isometric view of the wheel center and manually-operated stiffness adjustment mechanism of  FIG. 11 . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1A, 1B, 2, and 3  illustrate a first preferred embodiment of a variable stiffness wheel  10 . The variable stiffness wheel  10  includes a rim  11 , fixed flanges  12   b  and  13   b  and movable flanges  12   a  and  13   a  (also referred to as rings, plates and collars in this specification), and a plurality of wheel segments  17 ,  18  (e.g., two oppositely angled spokes  20 ) engaged with the flanges  12   a ,  12   b ,  13   a ,  13   b  and an outer traction element  16 . 
     The rim  11  includes an inner flange (not shown) which locates an adaptor plate and thereby allows the wheel  10  to be mounted on a spindle (not shown) which allows the variable stiffness wheel to rotate about the center axis. Preferably the spindle and mounting mechanism is similar to wheel mounting mechanism of present vehicles (e.g., secured by lug nuts). While the variable stiffness wheel  10 , as well as other embodiments of the present invention, are described as being used on a vehicle, it should be understood that these embodiments can be used on almost any device that may utilize a wheel, such as to support a conveyer belt or as a roller for a printer. 
     As best seen in  FIGS. 2 and 3 , the wheel segments  17 ,  18  are distributed evenly around the rim  11 . In the illustrated preferred embodiment, the wheel  10  includes about one hundred and twenty wheel segments  17  and  18  containing four different wheel segment planes (i.e., the planes formed by each spoke  20  of the segment  17  and  18 ). It should be obvious to anyone skilled in the art that the variable stiffness wheel  10  may include fewer or more wheel segments  17 ,  18  and fewer or more wheel segment planes. 
     The variable stiffness wheel  10  also includes sliding guides  15  engaged with the rim  11  and flanges  12   a ,  12   b ,  13   a ,  13   b  (the flanges  12   a  and  13   a  defining the movable wheel segments and the flanges  12   b  and  13   b  defining the nonmoving wheel segments) which affix the base of the plurality of wheel segments  17 ,  18  (i.e., the base of the spokes  20 ) to the rim  11 . Flanges  13   b  and  12   b  are positively affixed to the wheel to restrict linear movement along the axis of rotation. Flanges  12   a ,  13   a  slide along the guides  15  and are loaded (i.e., their position is changed) with preload adjusters  14  that are in contact with the flanges  12   a ,  13   a  and the rim  11 . In this respect, as the preload adjusters  14  (which move via actuators, not shown in these Figures) pull on the flange  13   a , force is transferred through guides  15  to flange  12   a , causing both flanges  12   a  and  13   a  to move towards the preload adjuster  14 . Similarly, the preload adjusters  14  release their load, causing the flanges  12   a  and  13   a  to move away from the preload adjusters  14 . 
     In an alternate preferred embodiment, all rings may be fixed in place, may slide relative to each other or may include some combination thereof. For example, the inner flanges  13   a  and  12   b  may be fixed in place while the outer flanges  12   a  and  13   b  may slide relative to the rim  11 . Further, each of the wheel segments  17 ,  18  can be configured to nest between adjacent wheel segments  17 ,  18  or be stacked in line with each other. 
       FIG. 2  illustrates a detail isometric view of the variable stiffness wheel  10  with the traction element  16  sectioned away to illustrate the rim  11 , sliding rings  12   a ,  12   b ,  13   a ,  13   b , and the plurality of wheel segments  17 ,  18 .  FIGS. 2 and 3  illustrate the variable stiffness wheel  10  in one particular preload position, where the spacing between the rings  12   a ,  12   b ,  13   a ,  13   b  is at a nominal position. Where the ring pairs ( 12   a ,  12   b  and  13   a ,  13   b ) are closest together, the radial preload on the wheel segments  17 ,  18  will be at its greatest. This results in the highest radial stiffness of the wheel. Where the ring pairs ( 12   a ,  12   b  and  13   a ,  13   b ) are furthest apart, the radial preload on the wheel segments  17 ,  18  will be at its lowest and the angle of the wheel segments  17 ,  18  is at their greatest angle with respect to the vertical applied load. Conversely, the lowest preload and weakest wheel segment angle provides the lowest radial stiffness of the wheel. 
     In the present preferred embodiment, each wheel segment  17 ,  18  includes two oppositely angled spokes  20  which connect to one of the flanges  12   a ,  12   b ,  13   a ,  13   b  and to the traction element  16 . Preferably the spokes  20  are coupled to the flanges  12   a ,  12   b ,  13   a ,  13   b  and to the traction element  16  with either adhesive or mechanical fasteners, or by overmolding traction element  16  onto spokes  20 . The spokes  20  can comprise a variety of rigid or semi rigid materials such as polymer or composite material. 
     The preload adjusters  14  preferably include an actuator (not shown in these Figures) which may be controlled by the vehicle or manually adjusted by a user at the wheel itself. In one example, the linear actuator may be a pneumatic actuator driven by a CTIS. In another example, the linear actuator may be an electrical actuator that receives power through a slip ring connection (e.g., similar to the slip ring connections used for communication and power in the turret of a tank) to a chassis electrical system. In yet another example, a linear actuator may be a screw positioned through the rim  11  and connected to the flanges  12   a ,  12   b ,  13   a ,  13   b , thereby causing the flanges to move axially. 
     Preferably, the vehicle includes a control system (e.g., a microprocessor and control software) for monitoring vehicle characteristics such as speed, wheel slippage (e.g., loss of traction on an icy terrain), roughness of terrain, etc., and adjusts the wheel firmness according to preset firmness profiles during vehicle operation. Preferably, a slip ring connection, as known in the art, can be used for communicating or controlling the mechanisms of the wheel  10 . In a more specific example, as the vehicle monitors the increasing speed, the microprocessor executing the control software of the vehicle then increases the firmness of the wheel to provide more desired vehicle handling at the higher speed. In an even more specific example, the control software of the control system may include multiple speed ranges so that when the vehicle is traveling at a speed within a predetermined speed range (e.g., between 1 and 20 MPH) the control system sets a predetermined tire firmness. 
     The control system may also be used for steering the vehicle by only modifying the firmness of a portion of the wheel (e.g., changing the firmness of half of the wheel). Similarly, the control system can adjust a portion of each wheel&#39;s firmness to improve handling characteristics of the vehicle, such as handling when cornering. 
     In other alternate preferred embodiments, the preload adjusters  14  may be actuated through other linear or rotary electromechanical, fluidic, magnetic, or other mechanisms of exerting a force at the base of the movable rings  13   a ,  12   a . In another alternate preferred embodiment, the wheel segments  17 ,  18  may be directly actuated radially or semi-radially, similar to a camera shutter. 
     In another alternate preferred embodiment, each spoke  20  includes an inner lumen filled with pressurized media  20   a . The pressure of the media within the lumen is increased or decreased to respectively increase or decrease the stiffness of the spoke  20 , and therefore adjust the softness of the wheel  10 . 
     In another alternate preferred embodiment, each spoke may be composed of shape memory alloys to increase or decrease the firmness of the spoke  20 . For example, the shape memory alloy may include two predetermined shapes such as a straight and curved shape or two different radii of curve shapes. Applying power to the shape memory alloy distorts the spokes  20  between the two predetermined shapes or alternately to curves in between the two predetermined shapes. In this respect, the firmness of the wheel can be adjusted. 
     In another alternate preferred embodiment, artificial muscles or similar contracting materials (e.g., biomaterials) may be used as a linear actuator as part of the preload adjuster to move the flanges  12   a ,  12   b ,  13   a ,  13   b  between different positions. 
     Other mechanisms of adjusting preload tension/compression on the plurality of wheel segments may also include utilization of smart materials like artificial muscles biomaterials, or the replacement of wheel segments with linear or rotary actuators (e.g., as discussed in the preferred embodiment of  FIGS. 7A and 7B ). 
       FIGS. 4, 5A, 5B, and 6  illustrate another preferred embodiment of the variable stiffness wheel  110 , comprising one or more toroid-shaped spoke rings  114  composed of a plurality of curved spokes  124 . One end of each spoke  124  of the spoke ring  114  is connected to a spoke collar  116  which slidably engages the wheel rim  118 . The other end of each spoke  124  is connected to the traction element  112 , preferably by adhesive, mechanical fasteners, or by overmolding (e.g., overmolding traction element  112  onto the spokes  124 ). 
     As seen best in  FIGS. 5A, 5B and 6 , the wheel  110  includes spoke collars (similar to the flanges or rings described in previous embodiment of this specification) which slide in the direction of the axis of rotation of the rim  118 . As the spoke collars  116  slide, the end of the spokes  124  connected to the collar  116  also slides, thereby changing the curve of the spokes and modifying the firmness of the wheel  110 . 
     The wheel  110  is preferably mounted to a vehicle by a mechanism presently known in the art. For example, a wheel center  120  is affixed to a vehicle&#39;s wheel spindle (not shown), transmitting torque from the wheel spindle through wheel center  120  to the spoke collar  116  through the sliding guides  122 . Torque then is transmitted through the spoke ring  114  to traction element  112  which is in contact with the road surface, imparting braking and tractive forces to the vehicle. Wheel stiffness is increased by exerting a lateral force to the toroid-shaped spoke rings  114  in the direction of the axis of rotation of the wheel  110 , away from the plane of symmetry (shown in  FIG. 4 ). Wheel stiffness is reduced by exerting a lateral force to spoke rings  114  towards the plane of symmetry. 
       FIG. 7A  and  FIG. 7B  illustrate another preferred embodiment according to the present invention of a wheel for automatically increasing radial spoke stiffness according to increasing vehicle speed. Generally, this stiffness adjustment is achieved by harnessing the force of a mass  210  (or optionally a plurality of masses) which rotates with the wheel, thereby exerting force on the wheel as it rotates to change the configuration of the spokes. 
     At least one tension mass  210  is attached to outer spoke collar  212  by flexible cable  214 . The flexible cable  214  is routed over a reaction pulley  216  which is attached to wheel rim  218 . When the wheel rotates slowly (as seen in  FIG. 7A ), the force exerted on outer spoke collar  212  from the mass  210  is low, allowing outer spoke collar  212  (i.e., movable collar) to be pulled closer to inner spoke collar  220  (non movable collar) by the keeper spring  226 . This results in relatively low tension in each spoke ring  222  which maintains the wheel in a “soft” configuration with an enlarged ground contact patch size of traction element  224 . As the rotational speed of the wheel increases (as seen in  FIG. 7B ), the tension mass  210  exerts an increasingly larger force on flexible cable  214 , forcing the outer spoke collar  212  to move away from inner spoke collar  220 . The movement of outer spoke collar  212  increases the tension in each spoke ring  222 , increasing the wheel firmness and decreasing the ground contact patch size of traction element  224 . 
       FIG. 8A  and  FIG. 8B  illustrate another preferred embodiment according to the present invention for pneumatically adjusting the stiffness of spokes  320 . An air spring  310  (and optionally a plurality of air springs) is affixed to wheel rim  312  and to the outer spoke collar  314 . All air springs  310  are in fluid communication with a central pressurized air source (not shown) via pneumatic tubing  316 . When air is supplied to pneumatic tubing  316 , the air springs  310  inflate and force the outer spoke collar  314  to move closer to the inner spoke collar  318  (i.e., moving from the position illustrated in  FIG. 8A  to the position illustrated in  FIG. 8B ). As with previously described embodiments, this movement of the outer spoke collar  314  decreases the tension in spoke ring  320  and increases the ground contact patch size of traction element  322  (i.e., decreases firmness of the wheel). 
     When a pressure relief valve (not shown) is opened, air flows out of air springs  310  and into pneumatic tubing  316  and is exhausted to atmosphere through pressure relief valve (not shown). The deflated air springs  310  allow the outer spoke collar  314  to move away from inner spoke collar  318  (to the position seen in  FIG. 8A ), increasing the tension in spoke ring  320  and decreasing the ground contact patch size of traction element  322 . This relationship may appear counterintuitive when compared with a pneumatic time, however this preferred embodiment of the wheel remains stiff if left in its native shape and will become more compliant by pushing the spoke rings inward to decrease the spoke tension. 
     Preferably, the pressurized air for the air springs  310  is provided through a hollow, pressurized vehicle axle spindle which couples and thereby seals to the wheel similar to currently known central tire inflation systems. This sealed region of the wheel is in communication with pneumatic tubing  316 , allowing the vehicle (e.g., a computer and software within the vehicle) to pneumatically control the air springs  310  and thus the firmness of the wheel. 
     It should be understood that many of the elements described in the embodiments of this specification can be mixed or incorporated with other embodiments set forth in this specification without departing from the present invention. 
     Referring to  FIG. 9 , a conveyor device  400  consists of a plurality of rollers  402  with a variable lateral compliance capability, as described in various embodiments of the present specification. However, since the rollers  402  typically have a greater relative width compared with wheels, a plurality of spoke segments may be included along the length of rollers  402 . The rollers  402  may be configured to freely spin or may be motorized for propelling luggage  404  in the direction shown with the arrow. 
     When a sensor (not shown) detects a piece of luggage  404  which should be routed to the leftmost conveyor chute  406 , or alternately a user wishes to change the route of the luggage, the lateral compliance of rollers  402  is modulated. In this respect the course or direction of luggage  404  is changed. Similarly, the lateral compliance of rollers  402  may be modulated to direct luggage to the rightmost conveyor chute  408 . 
       FIGS. 10A, 10B, 10C, 11, 12A and 12B  illustrate another preferred embodiment according to the present invention for manually adjusting the stiffness of spokes  510 . Generally, a handle  530  rotates a central cable spool  522  which increases or decreases a cable tension on outboard inner spoke collar  524  and inboard inner spoke collar  520 , thereby adjusting the tension of the spokes  510 . 
     The inboard inner spoke collar  520  is connected to the cable spool  522  by a flexible cable  512  (or optionally a plurality of flexible cables). The flexible cable  512  is routed over reaction pulleys  514  between the wheel rim  516  and wheel center  518 . Similarly, the outboard inner spoke collar  524  is connected to cable spool  522  by a flexible cable  512  (or optionally a plurality of flexible cables). The flexible cable  512  is routed over additional reaction pulleys  514  between wheel rim  516  and wheel center  518 . 
     In this respect, as the spool  522  winds the cable  512 , the pulleys  514  support the increased cable tension that moves both inner spoke collars  520  and  524  toward the center of the wheel. Thus, the tension of the spokes  510  is modified, similar to the previously described embodiments of this specification. 
     Referring to  FIGS. 11-12B , the cable spool  522  is attached to the wheel center  518  by fastener  526  and prevented from rotating with respect to wheel center  518  by engagement of a shear pin  528  (or optionally a plurality of shear pins) with wheel center  518 . The shear pin  528  is attached to handle  530  and is prevented from disengaging from wheel center  518  by helical spring  532 . 
     When the user wishes to increase spoke tension, the operator pulls the handle  530  laterally outward, disengaging the shear pin  528  from the wheel center  518 . After shear pin  528  is disengaged, the operator rotates the handle  530 , causing the cable spool  522  to rotate. When the cable spool  522  rotates, the flexible cable  512  is pulled onto the cable spool  522 , drawing the outboard inner spoke collar  524  and the inboard inner spoke collar  520  towards each other and increasing the tension in the spokes  510 . When a desired spoke tension is reached, the operator pushes the handle  530  laterally inwards, re-engaging shear pin  528  with the wheel center  518 . 
     Although the invention has been described in terms of particular embodiments and applications, one of ordinary skill in the art, in light of this teaching, can generate additional embodiments and modifications without departing from the spirit of or exceeding the scope of the claimed invention. Accordingly, it is to be understood that the drawings and descriptions herein are proffered by way of example to facilitate comprehension of the invention and should not be construed to limit the scope thereof.