Abstract:
The present invention is directed to mixers for viscometers and methods of using the same. Such inventions are applicable, for example, to industrial processes such as printing. One embodiment of the invention is directed to a viscosity control system including a viscosity sensor, a mixing element, a shaft fixedly attached to the mixing element, and an actuator interfacing with the viscosity sensor and the shaft. The annular mixing element is oscillatable about an axis lying in a plane tangent to a point on a wall of the mixing element. The shaft is centered about the axis. The actuator receives a signal from the viscosity sensor and rotates the shaft and the mixing element in an oscillating manner about the axis. In some embodiments, the shaft rotates through an angle of less than 360 degrees.

Description:
RELATED APPLICATIONS 
     This application is a continuation under 35 U.S.C. §120 of International Application No. PCT/US2010/028467, filed Mar. 24, 2010, which claims priority to U.S. Provisional Patent Application Ser. No. 61/162,802, filed Mar. 24, 2009. The entire contents of each of these applications are hereby incorporated by reference herein. 
    
    
     FIELD OF INVENTION 
     The present invention is directed to mixers for viscometers and methods of using the same. Such inventions are applicable, for example, to industrial processes such as printing. 
     BACKGROUND 
     Viscosity control is essential in many of today&#39;s manufacturing and printing processes. Viscosity is the measure of the resistance of a fluid to deformation by either shear stress or extensional stress, but is commonly perceived as the “thickness” or resistance to flow of a fluid. Viscosity can be an important quality of a finished product (e.g. a lubricant, paint, or ink) or can affect a finished product (e.g. printed material). Perhaps more importantly, an inappropriate viscosity can adversely affect modern industrial equipment. For example, if the viscosity of printing ink falls outside of an acceptable viscosity ranges, not only is print quality affected, but the printing press can also become fouled. 
     In many processes, viscosity is continuously monitored and adjusted as needed. In many cases, viscosity is adjusted by adding additional solvent and/or solute to a mixture. Such additions will not immediately integrate the mixture, and therefore neither effect the desired viscosity adjustment nor allow the user to determine with a viscometer whether the adjustment was sufficient to produce the desired viscosity. 
     A variety of mixers are used to mix industrial chemical, such as printing ink. These mixers suffer from a variety of drawbacks. First, conventional mixers can cost approximately $500. This cost must be multiplied by the number of vats to be mixed. Second, many conventional mixers incorporate a significant amount of air into the mixture, especially where the fluid level in the vessel is low. In addition to distorting a viscosity measurement, this air can degrade processes such a printing. 
     Accordingly, there is a need for an affordable device capable of mixing liquid without incorporating air. 
     SUMMARY OF THE INVENTION 
     The present invention relates to a mixer for incorporation with a viscometer. One aspect of the invention provides a viscosity control system including: a viscosity sensor, a mixing element comprising a peripheral wall, a shaft fixedly attached to the mixing element, and an actuator interfacing with the viscosity sensor and the shaft. The mixing element is oscillatable about an axis lying in a plane tangent to a point on the wall of the mixing element. The shaft is centered about the axis. The actuator oscillates the shaft and the mixing element about the axis. 
     This aspect can have a variety of embodiments. The annular mixing element can include a plurality of apertures extending through the wall. The apertures can be substantially circular. The actuator can include a piston housed at least partially within a cylinder. The shaft can include includes a lever arm rigidly attached to the shaft. The piston can include a piston rod that extends at least partially outside of the cylinder to engage the lever arm and oscillate the shaft in a first direction when a pressure is applied to the piston. The system can include an air fitting through which compressed air is supplied to the cylinder to apply pressure to the piston within the cylinder. 
     The actuator can include a flexible element having a first end and a second end. The first end can be attached to the lever arm and the second end can be attached to the cylinder. The flexible element can move from a neutral position to an extended position when pressure is applied to the piston in the cylinder. The flexible element returns to the neutral position and rotates the shaft in a second direction when the pressure in the cylinder is released. The flexible element can be a coil spring. The mixing element can be a cylinder. The range of oscillation can be less than 360°. 
     Another aspect of the invention provides a fluid mixer including a mixing element comprising a peripheral wall; a shaft fixedly attached to the mixing element; and an actuator interfacing with the viscosity sensor and the shaft. The mixing element is oscillatable about an axis lying in a plane tangent to a point on the wall of the mixing element. The shaft is centered about the axis. The actuator oscillates the shaft and the mixing element about the axis. 
     Another aspect of the invention provides a method for controlling a viscosity of a fluid. The method includes measuring the viscosity of the fluid using a viscometer; positioning a mixing element within the fluid, the mixing element being oscillatable about an axis lying in a plane tangent to a point on a wall of the mixing element; adding a substance to the fluid in response to a signal sent by the viscometer; and oscillating the mixing element about the axis to mix the substance with the fluid. 
     This aspect can have a variety of embodiments. The annular mixing element can oscillate through an angle of less than 360 degrees. The oscillating motion of the mixing element can be accomplished using a reciprocating motion of a piston within a cylinder to move a shaft fixedly attached to the mixing element. The method can include using compressed air to move the piston within the cylinder. The method can be a computer-implemented method. 
     Another aspect of the invention provides a computer-readable medium whose contents cause a computer to perform a method for controlling a viscosity of a fluid. The method includes: measuring the viscosity of the fluid using a viscometer; positioning a mixing element within the fluid; adding a substance to the fluid in response to a signal sent by the viscometer; and oscillating the mixing element about the axis to mix the substance with the fluid. The mixing element is oscillatable about an axis lying in a plane tangent to a point on a wall of the mixing element. 
     This aspect can have a variety of embodiments. For example, the computer-readable medium can be non-transitory and tangible. 
    
    
     
       FIGURES 
       For a fuller understanding of the nature and desired objects of the present invention, reference is made to the following detailed description taken in conjunction with the accompanying drawing figures wherein like reference characters denote corresponding parts throughout the several views and wherein: 
         FIG. 1  is a perspective view of a system including a mixer and a viscometer according to one embodiment of the invention. 
         FIGS. 2A and 2B  are top views of mixing elements according to embodiments of the invention. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     The present invention relates to a mixer for incorporation with a viscometer. Referring to  FIG. 1 , a viscosity control system  100  is provided. Viscosity control system  100  includes a viscometer. The viscometer can be any of a variety of known viscometers including falling piston, falling sphere, vibrational viscometers, rotation viscometers, Stabinger viscometers, and Stormer viscometers. Viscometers are available from a variety of sources including, for example, Norcross Corporation of Newton, Mass. 
     The embodiment depicted in  FIG. 1  includes a failing piston viscometer. The falling piston viscometer includes a supporting shaft  102  connected to bracket  104  for supporting tube  106 . Lifter cylinder  108  periodically lifted, thereby lifting piston  110 . After piston  110  is raised so that tube  106  fills with the liquid to be measured, lifter cylinder  108  and piston  110  are released, allowing piston  110  to fall by force of gravity and displace fluid in tube  106 . The piston  110 , moving in close proximity to tube  106  approximates the parallel plates test for viscosity. Various embodiments of falling piston viscometers are described in U.S. Pat. Nos. 5,959,196; 4,154,094; 3,686,931; 3,677,070; and 3,304,765, the contents of which are hereby incorporated herein by reference. Although lifter cylinder  108  and piston  110  are described with separate labels in this description, in certain embodiments lifter cylinder  108  and piston  110  are a single component and can be fabricated from the same material. 
     In one embodiment, lifter cylinder  108  is actuated by a pneumatic actuator (not shown) contained within unit  112 . Other means of actuation include electrical, mechanical, hydraulic, and the like. 
     The mixer includes a mixing shaft  116  coupled with a mixing element  118 . In some embodiments, the mixing element is a cylinder (i.e. a surface consisting of each of the straight lines that are parallel to a given straight line and pass through a given curve). In certain embodiments, mixing element is annular. In still other embodiments, mixing element  118  has a horizontal cross-section approximating a shape selected from the group consisting of: a square, a rectangle, a triangle, a circle, an oval, a polygon, a parallelogram, a rhombus, an annulus, a crescent, a semicircle, an ellipse, a super ellipse, and a deltoid. An exemplary mixing element  118   a  is depicted in  FIG. 2A . In still other elements, such as those depicted in  FIG. 2B , mixing element  118   b  is not continuous, but rather comprises at least one open end. Such embodiments include elements having a horizontal cross-section approximating a ‘Y’, a ‘U’, an ‘X’, and the like. 
     In some embodiments, mixing element  118  has a solid peripheral wall. In other embodiments, mixing element  118  includes one or more apertures  120  in the wall that promote mixing of the liquid as mixing element is moved. Apertures  120  can be circular or have a cross-section, e.g., approximating a shape selected from the group consisting of: a square, a rectangle, a triangle, a circle, an oval, a polygon, a parallelogram, a rhombus, an annulus, a crescent, a semicircle, an ellipse, a super ellipse, and a deltoid. 
     Mixing shaft  116  and mixing element  118  are attached by a fastening means such as a nails, screws, bolts, pins, rivets, welding, brazing, soldering, adhesives, crimping, press fitting, and the like. Mixing element  118  can be removably attached so that various mixing elements can be used with the same mixer to reflect various vessel shapes and fluid characteristics. 
     Mixing shaft  116  can be oscillated by a number of devices. In the embodiment of the invention illustrated by  FIG. 1 , mixing shaft is coupled with a lever arm  122 . Lever arm  122  contacts piston  124 , which is in one embodiment, pneumatically actuated. As lifter cylinder  108  is raised, air flows to cylinder  130 , causing piston  124  to extend outwards, pushing lever arm  122 , and rotating mixing shaft  116  and mixing element  118  in the negative θ direction. When air flow ceases, extension spring  126  acts depresses piston  124  and rotating mixing shaft  116  and mixing element  118  in the positive θ direction. 
     In embodiments of the invention wherein the mixing element  118  is configured at the same height as one or more of viscometer elements  102 ,  104 ,  106 ,  108 , or  110 , the range of oscillation of mixing element  118  will generally be limited to a range less than 360°. For example, the range of oscillation can be about 270°, 180°, 90°, 60°, 45°, 30°, and the like. In embodiments of the invention wherein the mixing element is configured at a height below viscometer elements  102 ,  104 ,  106 ,  108 , or  110 , the range of oscillation of mixing element  118  can extend beyond 360°. 
     A number of devices can be used to return piston to its resting position. For example, a cylinder  130  can contain a compression coil spring to push piston  124  back to a resting position. Cylinder  130  can include a bleed valve to allow for air to escape from cylinder  130  when air flow into the cylinder  130  ceases. Alternatively, air may return through a tube that provides the air. In another embodiment, mixer shaft  116  is coupled with a spring to return mixer shaft  116  and piston  124  to a starting position. In another embodiment, a tension spring is coupled to supporting shaft  102  and lever  122 . 
     In other embodiments, piston  124  and/or mixing shaft  116  are operated by electrical, mechanical, or hydraulic means such as a motor or a servo. 
     Lever  122  and piston  124  can be coupled in a variety of configurations. In one embodiment, lever  122  and piston  124  are held together, in whole or in part, by pressure by compression and/or tension. Such a configuration can be obtained through the embodiments described above wherein a spring applies force to push lever  122  against piston  124 . 
     In another embodiment, lever and piston are coupled by a mechanical linkage or linkages. Such linkages include nails, screws, bolts, pins, rivets, hinges, chains, cables, rope, string, and the like. 
     In some embodiments, bracket  132  provides support for mixer shaft  116  and supporting shaft  102 . Bracket  132  can include a variety of fasteners  134  and holes for coupling bracket  132  with a vessel holding a liquid. 
     In still further embodiments, collar  138  couples with mixer shaft  116  to support mixer shaft  116  in bracket  140 . Collar  138  can be adjustable (for example, by loosening a screw) in order to allow for the height of mixing element with regard to tube  106  to be adjusted. In other embodiments, mixing shaft  116  is machined to comprise a top portion having a larger diameter than the bottom portion. Such an embodiment would support the mixing shaft without a collar  138 . 
     The components described herein can be fabricated from a variety of materials including, but not limited to, copper, steel (including unfinished or galvanized), cast iron, brass, aluminum, titanium, nickel, other metals and metal alloys, polyvinyl chloride (PVC), chlorinated polyvinyl chloride (CPVC), cross-linked high-density polyethylene (PEX), polybutylene (PB), acrylonitrile butadiene styrene (ABS), and the like. Such materials should be substantially inert to the fluid to be mixed. Materials can be formed into the components described herein by a variety of processes including casting, molding, machining, milling, stamping, and the like. 
     The apparatus described herein allows for the mixing of low levels of fluids without introducing air to the fluid. As depicted in  FIG. 1 , mixing element  118  can, in some embodiments, have a height shorter than the height of tube  106 . Accordingly, if there is sufficient ink in the vessel to allow for the measurement of viscosity, mixing element will be submerged. 
     Although the embodiments described herein discuss the mixer integrated with a viscometer, the invention encompasses mixers that are capable of operation with or without a viscometer. Such mixers can be configured for mounting on a viscometer and/or according to the same or similar principles described herein. 
     The mixer provided herein can configured to operate in a variety of ways. In one embodiment, the mixer (and viscometer, if combined) are introduced to a vessel, which in some embodiments will or will not contain fluid at the time of mixer introduction. The mixer can be configured to operating independently from the viscometer or dependent on the viscometer. 
     In an independent configuration, the movement of mixing element  118  is not affected by the operation of the viscometer. For example, mixer continues to oscillate regardless of whether the viscometer is sampling the fluid. 
     In a dependent configuration, the movement of mixing element  118  is affected by the operation of the viscometer. For example, the mixer can normally operate at a set oscillation speed and/or frequency, but cease or reduce the oscillation speed/frequency when the viscometer is sampling the fluid. The viscometer can return to the normal oscillation speed frequency when the sampling is completed. 
     The foregoing specification and the drawings forming part hereof are illustrative in nature and demonstrate certain preferred embodiments of the invention. It should be recognized and understood, however, that the description is not to be construed as limiting of the invention because many changes, modifications and variations may be made therein by those of skill in the art without departing from the essential scope, spirit or intention of the invention.