PERISTALTIC PUMP HAVING A MOTOR
OVERLOAD PROTECTOR
This application is a continuation of application Ser. No. 07/558,051, filed Jul. 25, 1990, now abandoned.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a peristaltic pump suitable for use in, for example, transfusion.
2. Prior Art
Hitherto, various peristaltic pumps have been proposed as disclosed, for example, in Japanese Unexamined Patent Publication No. 56-113084. In general, a known peristaltic pump has a plurality of cams, a plurality of pressing fingers actuated by the cams so as to move between a retracted position and an operative position, and a platen opposing the pressing fingers so as to carry a tube therebetween. In operation, the pressing fingers are successively actuated to the operative position by the cams so as to collapse the tube, whereby a liquid in the tube is displaced and transported, while the elastic tube is allowed to restore when relieved from the pressing force so as to expand the liquid passage, thus performing a pumping action.
In the peristaltic pump of the type described, problems are caused such as damaging of the tube due to excessive pressing, unduly large load posed on the cam actuating device, and so forth, as a result of any dimensional errors caused during manufacture of the components such as the cams, pressing fingers and the platen, as well as insufficiency in the locating precision of these components. In order to obviate these problems, it has been proposed to provide an elastic support member on the back side of the platen opposite to the pressing fingers, so that any excessively large pressing force is absorbed by the elastic deformation of the supporting member thereby relieving and unburdening the platen.
When the platen is unburdened, the pressing force to be relieved acts only on a local point on the tube which is immediately under a certain pressing finger which has been set to the operative position. Therefore, during the unburdening, the platen does not always makes a translational movement. Namely, the platen may be moved at an inclination with respect to the plane of the group of pressing fingers. In such a case, the support of the tube on the platen is rendered unstable so as to impair the precision in control of the flow rate of the liquid during transfusion.
Under this circumstance, Japanese Unexamined Utility Model Publication No. 62-20182 discloses a peristaltic pump which is improved to eliminate the abovedescribed problems concerning unburdening of the platen. In this improved peristaltic pump, any excessive force which would unduly collapse the tube is relieved not by a displacement of the platen but by elastic deformation of an elastic buffering portion of each pressing finger made of an elastic material. Thus, any excessive force applied to a pressing finger, which would otherwise be exerted on the tube, is effectively absorbed by the pressing finger itself.
PROBLEMS TO BE OVERCOME BY THE
INVENTION
(A) This improved peristaltic pump disclosed in Japanese Unexamined Utility Model Publication No.
62-20182, however, still suffers from the following problems (J) and (5).
(1) Since the pressing finger is made of an elastic material and incorporates an elastic buffer portion, the
5 pressing surface of the pressing finger tends to be displaced by the elastic reaction force produced by the tube. It is therefore difficult to stably collapse the tube and, hence, to attain a stable pumping action. (5) Elastic buffer portions of different pressing fin
10 gers have different levels of absorption of excessive collapsing force and these levels are unadjustable. Therefore, when the elasticity or the size of the tube is changed to require a different levels of force absorption, replacement of all the pressing fingers or the whole
15 pump is inconveniently required.
Accordingly, an object of the present invention is to provide a peristaltic pump in which a tube is constantly and stably held by a platen to allow the tube to be collapsed stably by pressing fingers under normal operat
20 ing condition and, in the event of an application of any excessively large collapsing force, the excess of the collapsing force is absorbed without fail, thus realizing a stable pumping action. Another object of the present invention is to provide
25 a peristaltic pump which is improved to easily and freely adjust the level or ability to absorb excessive collapsing force in accordance with a change in the elasticity of the tube, size of the tube and other factors. (B) Another problem encountered with the known
30 peristaltic pump disclosed in Japanese Unexamined Patent Publication No. 56-113084 is not designed to stably set the entire part of the tube at proper position between the group of pressing fingers and the platen. This poses the following problems (T) and (2).
35 (?) The tube winds in the space between the pressing fingers and the platen, so that the length of the portion of the tube pressed by each pressing finger may differ from the design length.
(2) The portion of the tube to be pressed by each 40 pressing finger may be partly placed out of the area
where the pressing force by the pressing finger is exerted.
These problems (T) and (§) make it immpossible to press successive sections of the tube of a predetermined 45 length, thus impairing the precision of the flow rate control.
Accordingly an object of the present invention is to provide a peristaltic pump which enables a tube to be stably set at a proper position between a group of press50 ing fingers and a platen.
DISCLOSURE OF THE INVENTION
(A) To these ends, according to a first aspect of the present invention, there is provided a peristaltic pump
55 comprising: a plurality of eccentric cams; a cam shaft "carrying the cams and capable of driving the cams; a plurality of fingers adapted to be driven by the cams so as to press and collapse a tube: a platen arranged to oppose the group of fingers and capable of suppressing
60 the movement of the tube in the direction of the pressing; a movable member relatively movable toward and away from the platen and incorporating the cams, the cam shaft and the pressing fingers; and urging means for urging the movable member towards the platen;
65 wherein, when an excessively large pressing force is exerted on the tube by one of the pressing fingers, the movable member is moved away from the platen so as to reduce the pressing force exerted by the finger.
According to a second aspect of the present invention, there is provided a peristaltic pump of the first aspect, wherein the movable member is accommodated in a housing while the platen is secured to a door which is provided on the housing for movement between open 5 and close positions.
According to a third aspect of the present invention, there is provided a peristaltic pump of the second aspect, wherein the urging means includes an urging member disposed between the movable member and the 10 housing, and an adjusting member capable of adjusting the urging force of the urging member.
In the peristaltic pump of the first aspect of the invention, consecutive longitudinal sections of the elastic tube on the platen are successively collapsed as the 15 successive fingers of the finger group are activated, namely, the position on the elastic tube where the collapsing force is exerted is progressively moved in the longitudinal direction of the tube, so that the liquid in the tube is displaced, whereas the portion of the tube 20 relieved from the collapsing fore is allows to resume its original force by its elasticity so as to expand the liquid passage therein to suck a new portion of the liquid, whereby a pumping action is performed.
In the event that one of the pressing fingers is acti- 25 vated to exert an excessively large collapsing force, a correspondingly large elastic reaction force produced by the tube forces the movable member away from the platen against the urging force produced by the urging means. Consequently, the finger incorporated in the 30 movable member is moved together with the movable plate away from the platen, i.e., in the direction opposite to the collapsing force exerted by the finger, whereby the excessive portion of the collapsing force exerted by the pressing finger is absorbed. In conse- 35 quence, the tube is always stably held on the platen so that the tube is stably collapsed by the successive fingers during normal operation, whereas, when an extraordinarily large collapsing force is generated by a finger, the excessive portion of such a large collapsing 40 force is absorbed without fail, whereby a stable pumping action is performed.
According to the second aspect of the invention, a compact construction of the peristaltic pump of the first aspect can be realized by virtue of the fact that the 45 cams, fingers and the platen are housed in the housing through the door. Furthermore, the tube can easily be mounted in a proper position between the fingers and the platen through the door.
According to a third aspect of the present invention, 50 in the peristaltic pump of the first or the second aspect, an adjusting member is provided for enabling an adjustment of the urging force produced by the urging member which backs up the movable member against the elastic reaction force produced by the tube. Thus, the 55 level of force absorbed by a displacement of the pressing finger together with the movable member in the direction opposite to the collapsing force can easily be adjusted in accordance with a change in conditions or factors such as the elasticity of the tube, size of the tube, 60 and so forth.
(B) To these ends, according to a fourth aspect of the present invention, there is provided a peristaltic pump comprising: a plurality of eccentric cams; a cam shaft carrying the cams and capable of driving the cams, a 65 plurality of fingers adapted to be driven by the cams so as to press and collapse a tube; a platen arranged to oppose the group of fingers and capable of holding the
tube between itself and the fingers; and a tube holder disposed between the fingers and the tube and/or between the platen and the tube and having tube holding means which is provided on the surface of the tube holder contactable with the tube and capable of holding the tube in a predetermined position.
According to a fifth aspect of the present invention, there is provided a peristaltic pump of the fourth aspect, wherein the tube holder includes a sheet-type elastic member having a recess-type tube holding means formed in the surface thereof contactable with the tube.
According to a sixth aspect of the present invention, there is provided a peristaltic pump of the fifth aspect, wherein the tube holder includes at least a pair of tube clamping poritons projecting into the recess.
According to a seventh aspect of the present invention, there is provided a peristaltic pump of the sixth aspect, further comprising clamping fingers capable of pressing the clamping portions so as to enable the clamping portions to clamp the tube.
According to an eighth aspect of the present invention, there is provided a peristaltic pump of the fourth, fifth, sixth, or seventh aspect, further comprising: a housing accommodating the cams, a cam shaft and the fingers and supporting a tube holder such that the tube holder is located at a position where it opposes the tube to be mounted; and a door supported on the housing for movement between open and close positions and carrying the platen such that the platen opposes the tube.
According to a ninth aspect of the present invention, there is provided a peristaltic pump of the fourth, fifth, sixth, seventh, or eight aspect, wherein the surface of the tube holder to be contacted by the tube is made of a silicon rubber having a large coefficient of friction, while the surface of the tube holder to be contacted by the fingers is made of a fiuororesin having a small coefficient of friction.
According to a fourth aspect of the invention, consecutive longitudinal sections of the elastic tube on the platen are successively collapsed as the successive fingers of the finger group are activated, namely, the position on the elastic tube where the collapsing force is exerted is progressively moved in the longitudinal direction of the tube, so that the liquid in the tube is displaced, whereas the portion of the tube relieved from the collapsing fore is allows to resume its original force by its elasticity so as to expand the liquid passage therein to suck a new portion of the liquid, whereby a pumping action is performed.
In this fourth aspect, as well as in a fifth aspect, of the present invention, a tube is properly placed without any winding, by means of tube holding means on the tube holder, such that successive tube sections of the design length are placed in the pressing regions of the successive fingers, whereby the tube is correctly pressed by the successive pressing fingers at the successive sections so as to provide a high precision of control of the flow rate.
According to a sixth aspect of the present invention, the tube held by the tube holding means in the pump of the fifth aspect is clamped by a pair of clamp portions which are disposed at predetermined longitudinal position of the recess-type holding means, so that the successive sections of the tube can be properly located within the regions of the successive pressing fingers.
According to a seventh aspect of the present invention, the clamping portions of the tube holder in the sixth aspect of the invention are pressed by clamping
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