Patent Publication Number: US-2002001530-A1

Title: Tube pump

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a tube pump, more particularly to an improvement of a tube for use in the tube pump.  
       [0003] 2. Description of the Prior Art  
       [0004] A tube pump is configured such that a tube is disposed in a ring shape along a circular inner circumferential face formed in a housing and such that the tube is squeezed sequentially in the longitudinal direction thereof by a pressure application member disposed inward, such as a roller or a ring, so as to feed fluid from the inside of the tube. A straight tube, which is made of a rubber elastic material, circular or nearly circular in cross section and stretchable and compressible in both the radial and longitudinal directions, is generally used as a tube for this pump. This tube is bent in a ring shape and disposed along the inner circumferential face of the housing.  
       [0005] When the straight tube is bent during use as described above, the outer side of the bent tube is stretched, and the inner side thereof is compressed. Hence, if the curvature of the bent tube exceeds a certain limit, the tube results in buckling, and the buckling portion becomes flat, whereby the effective cross-sectional area of the tube becomes small and the pump cannot deliver its intended capacity. To prevent this problem, it is necessary to take countermeasures. For example, the diameter of the inner circumferential face of the housing is made larger to decrease the curvature thereof, or the wall thickness of the tube is made larger to make the tube resistant to flattening. However, these countermeasures become great factors making the size of the pump larger.  
       [0006] In addition, in order to operate the pump efficiently, the tube is required to be flattened completely so as not to cause any clearance inside when the tube is squeezed, and also required to return to its original shape promptly after squeezing. However, in the case of a tube being circular in cross section, in order to completely flatten this tube, it is necessary to apply a pressure force that is large enough to fold back the wall of the tube 180 degrees at both ends thereof in cross section. Furthermore, in order to allow the tube to return to its original shape promptly after squeezing, it is preferable that the elastic force of the tube is larger. Hence, it is necessary that the pressure force is large enough to cope with this large elastic force. Therefore, these also become great factors making the size of the pump larger. Moreover, these require extra energy significantly exceeding energy required for fluid transfer. As a result, the efficiency of the pump is lowered, and the tube is apt to break at portions wherein folding back is repeated, thereby increasing maintenance cost.  
       [0007] Still further, since a freely stretchable and compressible tube having rubber-like elasticity is required, the material of the tube that can be used for the pump is limited. Hence, it is impossible to use tubes made of synthetic resins having high chemical resistance, such as polypropylene, polyethylene and fluorocarbon resin, thereby causing a problem of limiting the application range of the pump.  
       SUMMARY OF THE INVENTION  
       [0008] In view of these problems, a first object of the present invention is to provide a compact tube pump. A second object of the present invention is to reduce energy required for pump operation. A third object of the present invention is to provide a tube pump comprising a tube being resistant to breakage. Furthermore, a fourth object of the present invention is to provide a tube pump having very few limitations on the material of the tube so as to be usable for wide applications.  
       [0009] In order to attain the above-mentioned objects, the tube pump of the present invention uses a tube formed beforehand into a shape adapted for the inner circumferential face of the housing.  
       [0010] The specific configuration of the tube pump of the present invention, more particularly the specific configuration of its tube, will become apparent from the following descriptions of embodiments of the invention. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0011]FIG. 1 is a schematic front view showing an embodiment of a tube pump in accordance of the present invention;  
     [0012]FIG. 2A is a perspective view showing a tube for use in the pump;  
     [0013]FIG. 2B is a sectional view showing a shape of the squeezed portion of the tube;  
     [0014]FIG. 3A is a sectional view showing another shape of the squeezed portion of the tube;  
     [0015]FIG. 3B is a sectional view showing still another shape of the squeezed portion of the tube;  
     [0016]FIG. 4 is a sectional view showing shapes of the pressure application faces of the pump and a further shape of the squeezed portion of the tube;  
     [0017]FIG. 5A is a sectional view showing a still further shape of the squeezed portion of the tube for use in the pump; and  
     [0018]FIG. 5B is a sectional view showing a squeezed condition of the still further shape of the squeezed portion of the tube. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     [0019] Referring to FIG. 1, numeral  1  designates a housing having an inner circumferential face  2 . On the inner circumferential face  2 , a circular pressure application face  2   a  is formed in a range larger than the half and smaller than the whole of the circumference of the inner circumferential face  2 . An opening portion  2   b  is provided at a portion wherein the pressure application face  2   a  is not formed. Numeral  3  designates a tube. The tube  3  is disposed along the inner circumferential face  2 . The straight extension portions  3   a  at both ends of the tube  3  are extended outside the housing  1  from the opening portion  2   b.    
     [0020] Numeral  4  designates a ring-shaped pressure application member disposed on the inner side of the tube  3 . The pressure application member  4  has a double structure comprising an inner ring  41  and an outer ring  42 . The inner ring  41  is made of a rigid material having a low friction coefficient, such as a fluorocarbon-resin-based synthetic resin mold. The outer ring  42  is formed of a mold made of an elastic material having a high friction coefficient, such as rubber. The outer circumference of the outer ring  42  is used as a pressure application face  4   b.    
     [0021] Numeral  5  designates an eccentric driving member disposed on the inner side of the pressure application member  4 . Numeral  6  designates a rotation shaft on which the eccentric driving member  5  is installed. The eccentric driving member  5  rotates for example clockwise as seen in FIG. 1 while its circular outer circumferential face  5   a  makes sliding contact with the inner circumferential face  4   a  of the pressure application member  4 . Hence, the pressure application member  4  carries out circular motion along the inner circumferential face  2  of the housing  1 , whereby the pressure application faces  2   a  and  4   b  hold the tube  3  therebetween and squeeze the tube  3  sequentially toward the left extension portion  3   a  as seen in FIG. 1. A drive motor (not shown) is disposed on the rear face of the housing  1 , and the output shaft of the motor is directly used as the rotation shaft  6  or connected to the rotation shaft  6  via an appropriate reduction gear.  
     [0022] The tube  3  is formed of a synthetic resin mold having a high chemical resistance, such as polypropylene, polyethylene and fluorocarbon resin. As a whole, the tube  3  has a shape shown in FIG. 2A. The straight extension portion  3   a  adapted for the opening  2   b  is formed at each end of the ring-shaped squeezed portion  3   c  adapted for the pressure application face  2   a  of the housing  1  so as to be integrated with the squeezed portion  3   c.  In addition, a connection portion  3   b  for connection to another apparatus via a tube is formed at the end of the extension portions  3   a.  The connection portion  3   b  is provided with appropriate annular projections to prevent disconnection. This tube  3  is not so flexible as rubber because it is a mold made of the above-mentioned material. Furthermore, the tube  3  has some hardness and rigidity, and also has elasticity so as to be deformable and so as to return to its original shape after deformation. The shape of the tube  3  shown in FIG. 2A is just an example, and it is needless to say that the tube  3  can be formed into a shape adapted for the inner circumferential face  2  of the housing  1  in which the tube  3  is used.  
     [0023]FIG. 2B is a sectional view taken along a plane in a direction perpendicular to the length of the squeezed portion  3   c.  In other words, its cross section has a flat shape wherein an outer side  3   d  making contact with the housing  1  is joined to an inner side  3   e  making contact with the pressure application member  4  at joint portions  3   f.  An angle A at which the outer side  3   d  intersects the inner side  3   e  is an acute angle. Both the outer side  3   d  and the inner side  3   e  have circular arc shapes slightly inflated outward. Since the squeezed portion  3   c  is extended in the direction of flatness of the tube  3 , the thickness of the outer side  3   d  and the thickness of the inner side  3   e  are far smaller than that of the extension portion  3   a.  In FIG. 2B, it is assumed that the cross sections of the outer side  3   d  and the inner side  3   e  have ordinary circular arc shapes. However, the cross sections may have circular arc shapes partially taken from ellipses.  
     [0024] Since the tube pump  11  of this embodiment comprises the tube  3  having the above-mentioned shape, the outer side  3   d  and the inner side  3   e  having small wall thicknesses and slightly inflated shapes should only be flattened at the time of squeezing. Since the angle at the joint portion  3   f  is an acute angle, the amount of its deformation is small at the time of squeezing. Furthermore, in the case of this deformation, both the ends are not folded back 180 degrees when flattened. Hence, the outer side  3   d  and the inner side  3   e  should only have elasticity to the extent that they can return to their inflated shapes. For this reason, the wall thicknesses of the outer side  3   d  and the inner side  3   e  can be made smaller. Therefore, the tube can be squeezed completely by applying a smaller pressure force in comparison with a case wherein a circular rubber tube is squeezed, and breakage at the joint portions  3   f  owing to repeated deformations is less likely to occur. Still further, since the deformations at the outer side  3   d  and the inner side  3   e  are small, they can return promptly to their original shapes after squeezing by virtue of the recovery forces of the outer side  3   d,  the inner side  3   e  and the joint portions  3   f.    
     [0025]FIGS. 3A and 3B show examples of other sectional shapes of the squeezed portion  3   c.  The shapes of the outer side  3   d  and the inner side  3   e  shown in FIG. 3A are formed of broken lines wherein the outer side  3   d  and the inner side  3   e  are inflated and bent outward thereby forming a rhombus. In addition to this rhombus, it is possible to have a flat hexagon or the like. Furthermore, the shape shown in FIG. 3B is similar to that shown in FIG. 2B, but the joint portions  3   f  have fin shapes extending in the direction of flatness of the tube  3 . The outer side  3   d  and the inner side  3   e  have shapes smoothly inflated in parallel with the fin-shaped joint portions  3   f.  Hence, deformations at the joint portions  3   f  are almost negligible, whereby the tube  3  can be squeezed easily to a flat shape. In this case, when the sum of the wall thickness of the outer side  3   d  and the wall thickness of the inner side  3   e  is made equal to the wall thickness of the joint portion  3   f,  and when the tube  3  is squeezed and flattened, the thickness of the tube  3  becomes constant on the whole.  
     [0026] Since the tube  3  is formed into the shape adapted for the inner circumferential face  2  of the housing  1  beforehand as described above, even when the housing  1  is small and when the curvature of the inner circumferential face  2  is large, no extension force applies to the outer side of the curved shape of the tube  3 , and no compression force applies to the inner side of the curved shape of the tube  3  during pump operation. Furthermore, the sectional shape of the squeezed portion  3   c  of the tube  3  that is squeezed during pump operation is a flat shape wherein the outer side  3   d  on the side of the housing  1  and the inner side  3   e  on the side of the pressure application member  4  are joined to each other at acute angles. Hence, the wall thickness of the squeezed portion  3   c  can be decreased, and the amount of its deformation at the time of squeezing can be reduced, whereby squeezing can be carried out securely by applying a relatively small pressure force.  
     [0027] With these overall effects, the size of the pump is prevented from being made larger, and breakage of the tube owing to repeated deformations does not occur because the amount of deformation of the tube is reduced. Furthermore, a variety of synthetic resins can be used as materials of the tube, whereby it is possible to obtain a tube pump applicable to a variety of medicines and chemical products.  
     [0028] Still further, this kind of pump is not used independently, but is required to be connected between external apparatuses via connection tubes in order to receive and deliver fluid to be transferred. In this embodiment, the connection to the external apparatuses is easy, since the connection portion  3   b  is formed at each end of the tube  3  so as to be integrated therewith as described above.  
     [0029] In the embodiment, it is assumed that the pressure application face  2   a  of the housing  1  and the pressure application face  4   b  of the pressure application member  4  are cylindrical and that their sectional shapes are straight in the axial direction. The squeezed portion  3   c  of the tube  3  is symmetrical with respect to its centerline in the direction of flatness of the tube  3 .  
     [0030] On the other hand, as shown in FIG. 4, one of the pressure application face  2   a  of the housing  1  and the pressure application face  4   b  of the pressure application member  4  can have a convex circular arc shape in cross section, and the other can have a concave circular arc shape in cross section adapted for the convex circular shape. In this case, it is preferable that the wall thickness of one of the outer side  3   d  and the inner side  3   e  of the tube  3 , making contact with the concave pressure application face, is made larger, and that the wall thickness of the other, making contact with the convex pressure application face, is made smaller. In FIG. 4, the pressure application face  4   b  is made convex, the pressure application face  2   a  is made concave, the wall thickness of the outer side  3   d  of the tube  3  is made larger, and the wall thickness of the inner side  3   e  is made smaller. In the case of this shape, the side that is thin and deformable easily at the time of squeezing, that is, the inner side  3   e  in the example shown in FIG. 4, can be deformed and pressed easily against the outer side  3   d  with no clearance therebetween as indicated in a chain line. Hence, no large pressure force is required for squeezing. Furthermore, after squeezing, the inner side  3   e  returns to its original shape by virtue of its elasticity.  
     [0031] Generally speaking, a thin object having a slightly inflated shape has the property of being deflated abruptly because of a kind of buckling phenomenon when an external pressure larger than the deflation pressure of the object is applied to the object and returning to its original shape abruptly when the external pressure becomes extinct. In the case of this tube  3 , by properly selecting the wall thickness and the inflated shape of the inner side  3   e,  the inner side  3   e  can be deflated easily by slight pressure application and can immediately return to its original shape when the pressure application ceases. By using this property, it is possible to obtain a tube wherein the inner side  3   e  can make completely close contact with the outer side  3   d  by applying a small pressure force and the inner side  3   e  returns promptly to its original shape after squeezing. This so-called can-deflating effect can be obtained by properly selecting the wall thickness and inflated shape. Hence, an effect similar to this effect can also be obtained even when the wall thickness of the outer side  3   d  is equal to that of the inner side  3   e.    
     [0032]FIGS. 5A and 5B show an example wherein the shape returning force of the tube  3  is improved by using a structure different from the above-mentioned structures. In this example, at least the squeezed portion  3   c  of the tube  3 , a synthetic resin mold, is covered with a rubber tube  8 . It is preferable that this rubber tube  8  has a size that achieves a slightly stretched condition when the tube  3  is covered with the rubber tube  8 . In this configuration, in a condition wherein the tube  3  is squeezed and flattened as shown in FIG. 5B, an inward contracting stress is produced in the stretched rubber tube  8  as indicated by the arrows. Hence, the returning force of the rubber tube  8  is superimposed on the returning force of the tube  3  itself, whereby the tube  3  can promptly return to its original shape after squeezing.  
     [0033] Unlike the structure wherein the tube  3  is covered with the rubber tube  8  shown in FIGS. 5A and 5B, for example, a structure, in which cushion members made of sponge or the like are disposed at positions making contact with the connection portions  3   f  at both ends of the tube  3  when squeezed and flattened, may be used. In other words, the forces for returning the connection portions  3   f  are generated by the cushion members. Even when this configuration is used, the tube  3  can return promptly to its original shape after squeezing.  
     [0034] As a result, with the above-mentioned configurations, the tube can return promptly to its original shape after the squeezing of the tube is completed, whereby it is possible to obtain an efficient tube pump.