US3740173A

US3740173A - Peristaltic pump

Info

Publication number: US3740173A
Application number: US00181052A
Authority: US
Inventors: S Natelson
Original assignee: Rohe Scientific Corp
Current assignee: Rohe Scientific Corp
Priority date: 1971-09-16
Filing date: 1971-09-16
Publication date: 1973-06-19
Anticipated expiration: 1990-06-19
Also published as: DE2245356A1; GB1383858A; CH544222A; IT967502B; NL7212071A; JPS4947914A; BE788703A; FR2154080A5

Abstract

A peristaltic pump wherein a roller drum is made to engage a curved press plate, the roller drum acting on tubing passing between the drum rollers and the press plate, the press plate has at least two longitudinal ridges normal to the drum rollers to prevent said drum rollers from pressing the tubing beyond its elastic limit. A guide and resilient means are applied to the press plate allowing the press plate freedom of movement and permitting the press plate to adjust to the configuration of the tubing. A flexible belt which is spring loaded covers the drum rollers to produce a smooth peristaltic motion on the tubing.

Description

11 1 3,740,173 1451 June 19,1973

United States Patent 1191 Natelson PERISTALTIC PUMP Prima ExaminerCarlton R. Cro 1e 75 1 1; s uelNtel nCh ,111. Y 1 men or am a so wage Assistant ExaminerRichard E. Gluck Attorney-George B. Oujevolk [73] Assignee: Rohe Scientific Corporation, Santa Ana, Calif.

Sept. 16', 1971 [21] Appl. No.: 181,052

[22] Filed:

ABSTRACT 52 us. (:1. 417/475, 417/477 A perstaltc pump whe'em a drum made 51 Int. Cl.

gage a curved press plate, the roller drum acting on new girl: 43/08 g' 2 tubing passing between the drum rollers and the press plate, the press plate has at least two longitudinal ridges normal to the drum rollers to prevent said drum rollers from pressing the tubing beyond its elastic limit. A

References Cited UNITED STATES PATENTS guide and resilient means are applied to the press plate allowing the press plate freedom of movement and per- 3,l01,l674 mitting the press plate to adjust to the configuration of 3,353,491 2,641,516

Weiskopf et 417/477 X Bastian the tubing. A flexible belt which is spring loaded covers 6/1953 Bakane 12/1954 the drum rollers to produce a smooth peristaltic motion on the tubing.

FOREIGN PATENTS OR APPLICATIONS Vensen 6 Claims, 9 Drawing Figures 10/1970 Germany 417/474 Patented June 19, 1973 3,740,173

'2 Sheets-Sheet 1' JMW INVENTOR.

Patented June 19, 1973 quuuuuuu (l 7 Sheets-Shoat 2 INVENTOR.

Pat ented Jqne 19. 1973 7 Sheets-Sheet 5 INVENTOR.

Patented June 19, 1973 3,740,173

'7 Sheets-Shut 4 Fig'4 Patented June 19, 1973 3,740,1 73

'7 Sheets-Sheet 5 Patented June 19, 1973 I 3,740,173

'7 Sheets-Shem 7 1 PERISTALTIC PUMP BACKGROUND or THE INVENTION BRIEF REVIEW OF THE PRIOR ART The peristaltic pump has been in use for over 300 years. Some of these pumps have been described by the present inventor in U.S. Pat. Nos. 3,305,097; 3,450,624; 3,495,541; 3,331,665 and 3,489,525. The advent of automatic systems of chemical analysis set up the requirement that peristaltic pumps be developed so as to pump fluids in a continuous manner at constant speeds forlong periods of time. While many versions of this purnp were developed, only one, where the rollers rnove across a flat bed, has been successful with regard to constant volume. These pumps are expensive and difficult to make because of the requirement that the roller milking the tubing move on a horizontal plane. It is rnore economical to build the rollers as part of a wheel, like a squirrel cage. A motor can then drive this wheel with the mounted rollers at constant speed.

Numerous pumps have appeared using this principle (see Natelson U.S. Pat. No. 3,489,525, FIG. 1). None hare actually been successful except for use as a pump where constant delivery of volume was not a requirement. Volumes are irregular and volumes keep changing with time. In order to maintain constant volumes in a rotary peristaltic pump certain requirements are neccssaryl. The tubes must not be subject to excessive pressure. if the elastic limit is reached they will not return to their original shape when the pressure is released.

2. The pressure must be adequate to seal the tube as the roller passes over the tube to maintain forward mo-. tion. I

3. It is almost impossible for rollers to be disposed in a perfect circle. The surface on which the tube rests, and over which the roller rolls must also be a perfect circle. In addition, the surface and the rollers need to be aligned so that the tubing is not caused to be distorted sideways. Some mechanism needs to be supplied to satisfy these requirements.

4. The pressure on the tubing needs to be constant at all times and not vary during the running of the rollers over the tubing. The operator must automatically be able to set to the same pressure as in the previous run if results are to be duplicated.

The present invention solves these problems in a simple fashion, so that an inexpensive pump can be built at a low cost which will operate on as many tubes, simultaneously, as desired (e.g. 3O tubes) keeping a constant flow continuously, over extended periods of time I SUMMARY OF THE lNVENTlON Briefly stated the present invention contemplates an improvement in a peristaltic pump wherein a roller drum is made to engage a curved press plate, said roller drum acting on tubing passing between the drum rollers and the press plate. The improvement contemplated herein is that the press plate has at least two longitudinal ridges normal to the drum rollers to prevent said drum rollers from pressing the tubing beyond its elastic Iirnit. A guide and resilient means are applied to the press plate allowing the press plate freedom of movement in all possible directions, thus permitting the press plate to adjust to the configuration of the tubing.

The invention, as well as other objects and advantages thereof will become apparent from the following detailed description when taken together with the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 presents an overall perspective view of one version of the assembled pump;

FIG. 2 shows a view of the pump from the side opposite to FIG. 1 with the cover removed so that the rollers can be seen in place on the rotor shaft; the tubing is also in place, held in plastic plates with grooves;

FIG. 3 depicts the rotor with the rollers disposed in a circular mode so that they revolve with the rotor shaft and can also rotate on their axles as they move across the tubing;

FIG. 4 illustrates the pump press plate from the top;

FIG. 5 is a view of the press plate from the bottom;

FIG. 6 shows the plastic supports and the mechanism for mounting the supports on the pump housing;

FIG. 6a shows a perspective view of one of the crosspieces used herein when turned upside down; and

FIG. 6b is a cross-sectional of the tubing in the press plate of the pump being squeezed by a roller;

FIG. 7 shows how a spring loaded flexible belting is disposed over the rollers to even out the pressure to the tubes being milked.

Looking first at FIG. 1, there is shown in the drawing the pump 10, which includes a frame or housing shown as a rectangular box 12. The pump 10 will act on plastic tubing 14 which is held in plastic tubing support 16. Plastic tubing support 16 consists of rectangular plastic pieces which extend along both ends of the top of box 12. Tubing support 16 has horizontal grooves 18 the tubing 14 passing along these grooves. Thus, the plastic tubing 14 extends across the top of box 12 and passes out of the tubing support. Plastic or rubber stops 20 hold the tubing in place. Disposed over the plastic tube support 16 is a metal crosspiece 22. This metal crosspiece goes over the ends of the box and its size corresponds to that of the plastic support. Again, over the metal crosspieces 22 are metal supports 24. These metal supports extend parallelto the sides of the box and extend between the two metal crosspieces. To hold the plastic tube support 16, the metal crosspieces 22 and the metal supports 24 are threaded rods26 at the four corners of the box. The plastic tube support, metal crosspieces and metal supports have apertures 26a corresponding to the location of these threaded rods. These components are held fast by wing nuts 28. Over the center of the box is a center crosspiece 30 held by a metal rod 32 withv a flat top 34. Seen on the outside of the housing box 12 is a drive shaft 36 with a sprocket 38 for motor drive. This drive shaft is connected into the box by a bearing assembly 40.

In FIG. 2 the cover of box 12 is removed and one of the sides with the input shaft 36 is rendered transparent. Also, the plastic tube support 16 is shown with grooves 18 to hold the plastic tubing. In the center of box 12 there is a drum 44 mounted on drive shaft 36. Around the periphery of drum 44 are a plurality of rollers 46 disposed parallel to the cylindrical axis of the drum. The tubing 14 is curved over the rollers and the action of the rollers 46 on the tubing 14 defines a pressing zone. Drum 44 is best seen in FIG. 3, and consists of two end plates 48 holding rollers 46, with the main shaft 36 passing axially through the drum, the end plates are rigidly attached to the shaft. At both ends of the main shaft 36 are bearing assemblies 40. These bearing assemblies are for roller bearings 50. But, beside the conventional outer and inner races, there is a flexible rubber center 52. This rubber or resilient center is very important for reasons which will be apparent shortly. The drive sprocket 38 is in turn driven by a chain 54, and a motor 56 driving a sprocket 58.

Disposed over the tubes, as shown in FIGS. 4 and 5, is a press plate 60. This press plate 60 is a section of a cylinder and will hold the tubes against the rollers. Over the press plate 60 is the metal support 24 held by crosspieces 22. At the center is center crosspiece 30 shown transparent to explain the construction. Passing through the press plate are vertical metal rods 32 with a flat head 34. Under the center crosspiece 30 on these rods, between the metal support 24 and the press plate 60 are springs 62. Rods 32 pass through both the center crosspiece 30 and the metal support 24 through apertures 64. These apertures 64 are quite wide allowing considerable lateral movement of the rods 32. Looking at the press plate from the underside, as shown in FIG. 5, there is a ridge 66 about 3/64 inch along the sides and across the center of the press plate extending downwards. This ridge is parallel to the direction in which the tubing .will pass.

The placing of the tubing in the pump will be apparent from FIGS. 6 and 6a. The tubing 14 is stretched across the box'and the plastic tube supports 16 are placed over the tubing. These tube supports 16 have slots or grooves 18, best seen in FIG. 6a.

FIG. 7 illustrates an attachment which serves to decrease the wear on the tubing carrying the specimen and allows a smoother action of the pump. 70 is a 3/64 inch thick sheet of high speed belting. The rough side faces the rollers and the smooth side is on top. This belting wraps around the rotor and is supported on the base of the pump housing by springs 71. As the drum 44 turns, the rollers 46 are made to rotate on their axes by contact with belting 70. When the pump is assembled as shown in FIG. 1, the tubing will be compressed between the belting and floating head. As the drum rotates the rollers traverse to the underside of the belting, lifting it and thus progressively applying pressure to the tubes causing a smooth peristaltic action. In this version the wear is taken mostly by the durable high speed belting, thus increasing the life of the tubes.

The fundamental concept behind the present invention is that the press plate 60 will float over the tubing. After lengthy studies of the causes of pumping difficulties with peristaltic pumps, it was found that the press plate must constantly adjust to the tubing and must therefore float over the tubing. For this reason, apertures 26a for the'end crosspieces, and aperture 64 for rod 32 at the center crosspiece, are quite wide allowing for considerable forward, backward, and lateral movement of the press plate. Furthermore, the ball bearing assembly 40 has a rubber resilient center 52, which also allows considerable movement of the drum when pressing the press plate against the tubing. To enhance the floating effect the press plate over the tubing is spring loaded by springs 62 and floats freely so that it can adjust, in three dimensions to the vagaries of the squirrel cage wheel. Two or even four powerful springs apply adequate pressure to close the tubes as the rollers move across them. This requires about 7 pounds per tube, or a total of 84 pounds. The press plate over the tubes is recessed exactly 3/64 of an inch so that the tubes can be compressed with this thickness as a limit. This prevents the pressure on the tubes beyond their elastic limit and assures a long life of constant delivery from these tubes. The wall thickness of the tubing used is 3/64 inch so that the two walls together make 6/64 inch. The design of the cover and the instrument in general is simple so that its total cost is very inexpensive,and this includes a 30 r.p.m. motor with a brake, capable of delivering pounds per square inch pressure. This is shown in FIG. 6 b, showing the press plate 60 with the ridge 66 and the tubing 14 in cross-section; The roller cannot compress the tubing past the3/64 inch ridge.

OPERATION OF THE PUMP In order to operate the pump, the tubing is placed in the slots of two plastic supports and stretched so that the supports can be slipped over the threaded rods as seen in FIG. 6. The pump now appears as in FIG. 2, with the plastic tubing stretched over the rollers. The press plate is now secured in place by slipping the apertures at the comers of the supports of the press plate, over the threaded rod and tightening the press plate and support in place by means of the wing nuts. The instrument now appears as in FIG. 1.

The wing nuts are now tightened fully so that the two crosspieces, at the end of the press plate support, meet the plastic tube support which acts as a stop. This compresses the springs. The position taken each time and the tension on the springs is the same since the topsupport is always necessarily tightened to the same point where crosspiece and plastic tubing support meet flush, thus acting as a stop.

The speed of the rotor is determined by the r.p.m. of the motor and the ratio of the teeth on the sprocket of the rotor and the motor. Speed may be changed by changing the motor speed or the teeth ratio of the sprockets. This can be seen in FIG. 3. It will also be noted in FIG. 3 that the rotor shaft is disposed on a ball bearing support so that it rotates smoothly but is also supported on the semi-hard rubber center support so that it has some give to it when pressure is applied to the rotor.

When the motor is turned on, the press plate is seen to rock gently as it takes up irregularities of the rotor, it also swivels laterally. Thus, the rotor floats while being spring loaded, correcting for the lack of alignment and circularity of the rotor. The tubing needs to be at right angles to both the rotor and the press plate. Any error in the location of the press plate relative to the rotor in this regard is automatically corrected as the press plate takes the position of least resistance. The tubes are pressed gently but never mashed because of the protection the ridges (3/64 inch) provide. Thus the plastic tubes are compressed but not pressed to the point beyond their elastic limit.

In running a plastic pump, the first few minutes is taken up in stretching the tubing to a point of balance.

During this period the rate of flow increases as the tubing is compressed and resistance to the motor decreases, the motor running faster as the load decreases. After this point of balance is reached the pump described will pump for many hours at constant speed.

For simplicity of demonstration, the press plate is shown tightened down with wing nuts. In actual practice the support of the press plate is fitted on the end with clamps similar to those which close a valise or travel trunk. The press plate support is then placed on the pump, and the four rods mounted on the housing are slipped through the holes at the end as a guide. The clamps are then tightened down on catches on the housing as one closes a valise or travel trunk for a quick connect or disconnect, if one should so desire.

Thus, this invention solves a problem which has been under study for many years, namely, how to make a rotary peristaltic pump for a plurality of tubes which will maintain constant flow in each tube. It does this by the application of two new ideas.

1. It provides a recess in a cylinder press plate to prevent the tubes from being over compressed. The roller actually rides on ridges.

2. It allows the press plate to float, under constant pressure in any of the three dimensions. It can move up, down or sway from side to side during the running of the pump, maintaining constant pressure on the tubes at all times. At all times the press plate assumes the position of least resistance.

As a further aid for this purpose, the rotor rides on ball bearing supported in stiff, but flexible rubber. This permits the rotor to also move slightly in any direction so as to aid in assuming a position of least friction with the press plate and aid the press plate in taking the proper position with respect to the rollers.

It is to be observed therefore that the present invention provides for a peristaltic pump for delivering measured and constant amounts of liquid per unit of time from a plurality of containers through a plurality of flexible tubes which are stretched between two supports. This is accomplished by means of rollers circularly disposed around a circular drum rotor, the flexible tubes being disposed over, in contact, and at right angle to the rollers which are mounted so that they may rotate due to the friction as they slide across the flexible tubes. The rotor is supported on an axle which is in turn supported by two bearings with flexible central support, e.g., rubber, so that it can revolve smoothly on the shaft. The drum rotor being made to revolve at constant speed by means of a motor drive. A press plate in the shape of a portion of a hollow cylinder is made to press on the flexible tubes and thus on the rollers by springs held in place by a rigid support in such a manner that the press plate may have the capability of some movement in any direction. The press plate is countersunk on the concave side to provide ridges of somewhat lesser height than the combined thickness of opposite walls of the flexible tubing so that the flexible tubing will be closed by the rollers but never compressed beyond its elastic limit. Thus, when the rotor rotates, the rollers pass over the flexible tubing successively, to drive the liquid in the flexible tubes in the same direction as the motion of the rotor, the press plate assuming different positions so as to conform to variations in the height and position of said rollers, resulting in an even and constant flow of liquid in each of the flexible tubes.

The use of a rotary design of the peristaltic pump permits (as showin in FIG. 7) the application to a thin flexible material over the rollers. The rollers now move within this flexible covering, which we will now call belting for convenience. When the pump is assembled, the tubing carrying the liquid being pumped is now disposed between the beltingand the press plate. As the pump revolves it presses on the belting which in turn presses on the tubing causing the liquid to flow. The scuffing of the rollers over the tubing is eliminated and the belting takes up this wear. The tendency of the peristaltic pump to stretch the tubes in the forward direction is also minimized for the same reason. This increases the life of the tubing markedly. A belting suitable for this purpose is conventional high speed belting, 3/64 inch thickness, which is smooth on the side contacting the tubing and rougher on the rotor side. Thus, the rollers are induced to rotate by the belting, which takes the wear, and not the tubing. For this reason the tubing is not stretched forward to a great extent which also increases its life span.

I claim:

1. A peristaltic pump, comprising in combination:

a. a housing including spaced apart tube supports for holding tubing between said supports;

' b. a drum rotor member with a central drive shaft to drive said drum rotor member disposed between said tube supports, the drive shaft being disposed normal to tubing extending between said tube supports, with rollers disposed around the periphery of said drum rotor member parallel to said drive shaft so as to engage tubing extending between said tube supports, also bearing assemblies including a flexible inner center disposed in said housing to support said drive shaft for rotation;

c. a floating arcuate press plate, said press plate forming a section of a cylinder whose axis somewhat coincides with said drum axis, the concave side of said press plate being disposed over said drum rotor member and generally conforming to the curvature of said drum rotor member, said press plate serving to hold tubing against said rollers, said press plate having at least two arcuate longitudinal ridges parallel to tubing extending between said tube supports, said ridges preventing the tubing from being pressed beyond its elastic limits; and,

(1. extended support means disposed over said press plate and connected to said housing, said press plate connected to said support means by loose connecting means allowing said press plate considerable movement up and down and from side to side over a wide space, whereby when the drum rotor member rotates, the rollers pass over the flexible tubing successively to drive liquid in the flexible tubing in the same direction as the motion of the rotor, the press plate assuming different positions so as to conform to variations in the height and position of said rollers, the press plate floating while being spring loaded, correctingfor lack of alignment and circularity of the drum rotor member.

2. A pump as claimed in claim 1, said ridges being substantially along the press plate edges.

3. A pump as claimed in claim 1 wherein said loose connecting means comprises at least one large opening in said support means, at least one thin connecting rod extending from said press plate side other than said concave side through said opening for substantial up and down and side to side movement therein, and, said resilient means being between said press plate other side and said extended support means.

4. A peristaltic pump as claimed in claim 1, including a frame, a flexible sheet of material covering said drum rollers so disposed as to be between said drum rollers and tubing acted upon by said drum rollers, and resilient means fastened to said frame holding said sheet over said drum rollers.

5. A peristaltic pump, comprising in combination:

b. a drum rotor member with a central drive shaft to drive said drum rotor member disposed between said tube supports, the drive shaft being disposed normal to tubing extending between said tube supports, with rollers disposed around the periphery of said drum rotor member parallel to said drive shaft so as to engage tubing extending between said tube supports, also bearing assemblies including a flexible inner center disposed in said housing to support said drive shaft for rotation;

c. a floating arcuate press plate, said press plate forming a section of a cylinder whose axis somewhat coincides with said drum axis, the concave side of said press plate being disposed over said drum rotor member and generally conforming to the curvature of said drum rotor member, said press plate serving to hold tubing against said rollers; and,

d. extended support means disposed over said press plate and connected to said housing, said press plate connected to said support means by loose connecting means allowing said press plate considerable movement up and down and from side to side over a wide space, whereby when the drum rotor member rotates, the rollers pass over the flexible tubing successively to drive liquid in the flexible tubing in the same direction as the motion of the rotor, the press plate assuming different positions so as to conform to variations in the height and position of said rollers, the press plate floating while being spring loaded, correcting for lack of alignment and circularity of the drum rotor memher.

6. A peristaltic pump, comprising in combination:

b. a drum rotor member with a central drive shaft to drive said drum rotor member disposed between said tube supports, the drive shaft being disposed normal to tubing extending between said tube supports, with rollers disposed around the periphery of said drum rotor member parallel to said drive shaft so as to engage tubing extending between said tube supports, also bearing assemblies disposed in said housing to support said drive shaft for rotation;

d. extended support means disposed over said press plate and connected to said housing, said press plate connected to said support means by loose connecting means allowing said press plate considerable movement up and down and from side to side over a wide space, whereby when the drum rotor member rotates, the rollers pass over the flexible tubing successively to drive liquid in the flexible tubing in the same direction as the motion of the rotor, the press plate assuming different positions so as to conform to variations in the height and position of said rollers, the press plate floating while being spring loaded, correcting for lack of alignment and circularity of the drum rotor member.

Claims

1. A peristaltic pump, comprising in combination: a. a housing including spaced apart tube supports for holding tubing between said supports; b. a drum rotor member with a central drive shaft to drive said drum rotor member disposed between said tube supports, the drive shaft being disposed normal to tubing extending between said tube supports, with rollers disposed around the periphery of said dRum rotor member parallel to said drive shaft so as to engage tubing extending between said tube supports, also bearing assemblies including a flexible inner center disposed in said housing to support said drive shaft for rotation; c. a floating arcuate press plate, said press plate forming a section of a cylinder whose axis somewhat coincides with said drum axis, the concave side of said press plate being disposed over said drum rotor member and generally conforming to the curvature of said drum rotor member, said press plate serving to hold tubing against said rollers, said press plate having at least two arcuate longitudinal ridges parallel to tubing extending between said tube supports, said ridges preventing the tubing from being pressed beyond its elastic limits; and, d. extended support means disposed over said press plate and connected to said housing, said press plate connected to said support means by loose connecting means allowing said press plate considerable movement up and down and from side to side over a wide space, whereby when the drum rotor member rotates, the rollers pass over the flexible tubing successively to drive liquid in the flexible tubing in the same direction as the motion of the rotor, the press plate assuming different positions so as to conform to variations in the height and position of said rollers, the press plate floating while being spring loaded, correcting for lack of alignment and circularity of the drum rotor member.

5. A peristaltic pump, comprising in combination: a. a housing including spaced apart tube supports for holding tubing between said supports; b. a drum rotor member with a central drive shaft to drive said drum rotor member disposed between said tube supports, the drive shaft being disposed normal to tubing extending between said tube supports, with rollers disposed around the periphery of said drum rotor member parallel to said drive shaft so as to engage tubing extending between said tube supports, also bearing assemblies including a flexible inner center disposed in said housing to support said drive shaft for rotation; c. a floating arcuate press plate, said press plate forming a section of a cylinder whose axis somewhat coincides with said drum axis, the concave side of said press plate being disposed over said drum rotor member and generally conforming to the curvature of said drum rotor member, said press plate serving to hold tubing against said rollers; and, d. extended support means disposed over said press plate and connected to said housing, said press plate connected to said support means by loose connecting means allowing said press plate considerable movement up and down and from side to side over a wide space, whereby when the drum rotor member rotates, the rollers pass over the flexible tubing successively to drive liquid in the flexible tubing in the same direction as the motion of the rotor, the press plate assuming different positions so as to conform to variations in the height and position of said rollers, the press plate floating while being spring loaded, correcting for lack of alignment and circularity of the drum rotor member.

6. A peristaltic pump, comprising in combination: a. a housing including spaced apart tube supports for holding tubing between said supports; b. a drum rotor member with a central drive shaft to drive said drum rotor member disposed between said tube supports, the drive shaft being disposed normal to tubing extending between said tube supports, with rollers disposed around the periphery of said drum rotor member parallel to said drive shaft so as to engage tubing extending between said tube supports, also bearing assemblies disposed in said housing to support said drive shaft for rotation; c. a floating arcuate press plate, said press plate forming a section of a cylinder whose axis somewhat coincides with said drum axis, the concave side of said press plate being disposed over said drum rotor member and generally conforming to the curvature of said drum rotor member, said press plate serving to hold tubing against said rollers; and, d. extended support means disposed over said press plate and connected to said housing, said press plate connected to said support means by loose connecting means allowing said press plate considerable movement up and down and from side to side over a wide space, whereby when the drum rotor member rotates, the rollers pass over the flexible tubing successively to drive liquid in the flexible tubing in the same direction as the motion of the rotor, the press plate assuming different positions so as to conform to variations in the height and position of said rollers, the press plate floating while being spring loaded, correcting for lack of alignment and circularity of the drum rotor member.