Rotary torque-to-axial force energy conversion apparatus

Details Rotary torque-to-axial force energy conversion apparatus Rotary torque-to-axial force energy conversion apparatus

1999-08-24

2001-02-20

Snow, Bruce (Department: 3738)

Prosthesis (i.e., artificial body members), parts thereof, or ai

Corporeal artificial heart, heart assist , control...

Having flexible diaphragm or chamber

C623S003110

Reexamination Certificate

active

06190409

ABSTRACT:

TECHNICAL FIELD
The present invention relates in general to an energy conversion apparatus employing a magnetic coupling for converting rotary torque to axial force or axial force to rotary torque. A significant application of the energy conversion mechanism is in the field of artificial hearts wherein the mechanism can be employed in an actuator for a ventricle assist device (VAD) or for pumping blood from one or two ventricles of a total artificial heart (TAH).
BACKGROUND ART
Implantable blood pumps or artificial hearts have been the subject of significant work for several decades. Although much progress has been made, no approach has demonstrated the high reliability needed for an actuator. Generally, most existing approaches employ conversion of the motion of a rotary electric motor into the linear motion of a pusher plate to squeeze blood from rubber-type ventricles. Some employ a hydraulic piston to squeeze the ventricles with fluid, while some push on the ventricles directly using no hydraulics. Such rotary-to-linear conversion mechanisms, including lead screws, gear pumps and a host of other designs, are all prone to primary component wear and breakdown. Thus, most, if not all, existing actuator approaches have undesirable reliability concerns associated therewith. In fact, existing actuator approaches comprise a major stumbling block in attaining a highly reliable, light weight prosthesis.
One type of artificial heart is depicted in
FIGS. 1
,
2
a
&
2
b
. This total artificial heart (TAH)
10
, provided by the Cleveland Clinic, includes blood inflow ports and valves
12
and blood outflow ports and valves
14
. As best shown in
FIGS. 2
a
&
2
b
, the TAH
10
includes two blood pumps, a right blood pump or ventricle
20
and a left blood pump or ventricle
22
within a housing
18
. Each blood pump
20
&
22
includes a reciprocable diaphragm
21
&
23
, respectively, which is mechanically coupled to a corresponding pusher plate
21
′ &
23
′ powered by an interventricular energy converter or actuator
26
. Actuator
26
, which pilots a guide pin
25
affixed to pusher plate
21
′ and a guide pin
27
affixed to pusher plate
23
′, produces an axial reciprocating motion which, during eject mode, drives one pusher plate
21
′ or
23
′ towards the TAH
10
housing
18
.
The heart is controlled by responding to venous pressure, because more flow is required as pressure increases. The follower is not directly coupled to either pusher plate. Thus, while blood from one blood pump is being ejected, the other is free to fill, with the rate of filling depending on venous return pressure. During fill, each guide pin is free to slide within the actuator, so diaphragm fill cycle motion is determined by venous pressure, rather than the actuator rate. Control logic senses the velocity or position of the diaphragm, and maintains an actuator speed sufficient to avoid fill cycle contact between pusher plate and actuator, without running so fast that efficiency or operation of the opposite pump is impacted. A ventricular assist device operates similarly, except that only one pump is involved.
The TAH
10
can be equivalently operated by a number of different, existing interventricular actuators. For example, most existing electromechanical actuators could be employed. The Cleveland Clinic—type TAH conventionally employs an electrohydraulic energy conversion apparatus. This apparatus comprises a brushless DC motor which turns a gear pump that provides hydraulic flow at about 100 psi. Internal valving controls flow to a double-ended hydraulic actuator. To ensure that the system is hermetically sealed, the actuator piston is actually a stack of magnets riding in the cylinder, with a follower magnet outside the cylinder to match piston motion. The follower magnets are attached to a translating element that presses against a pusher plate that deflects the rubber diaphragm. For further information on this actuator, reference: Massiello et al., “The Cleveland Clinic—Nimbus Total Artificial Heart,” Journal of Thoracic and Cardiovascular Surgery, Vol. 108, No. 3, pp. 412-419 (1994); and Harasaki et al., “Progress in Cleveland Clinic—Nimbus Total Artificial Heart Development,” ASAIO Journal, M494-M498 (1994).
Although existing energy conversion approaches have been successful to varying extents, the art would be advanced by a next-generation actuator for permanently implantable pulsatile ventricle assist devices and/or total artificial hearts which eliminates mechanical contact and wear between the principal rotary-to-linear motion conversion elements. The present invention provides this advancement.
DISCLOSURE OF INVENTION
Briefly summarized, the invention comprises in a first aspect a rotary torque-to-axial force energy conversion apparatus which includes a rotatable member and a translatable member. A magnetic coupling is provided between the rotatable member and the translatable member for converting rotary torque of the rotatable member to an axial force on the translatable member. The magnetic coupling may comprise permanent magnets including a first permanent magnet comprising part of the rotatable member and a second permanent magnet comprising part of the translatable member.
In one embodiment, the first permanent magnet comprises interleaved, helical magnet sections of alternating polarities, as does the second permanent magnet. These helical structures have the same pitch. The translatable member resides at least partially within the rotatable member, and the apparatus includes a mechanism for preventing rotation of the translatable member such that rotary torque of the first permanent magnet is converted to axial movement of the second permanent magnet, and hence the translatable member. The apparatus for imparting rotary torque to the rotatable member can comprise a permanent magnet rotary motor which imparts oscillating motion to the rotatable member, thereby producing an oscillating rotary torque at the first permanent magnet that in turn produces reciprocating axial movement in the second permanent magnet, and hence the translatable member.
In a further aspect, the invention comprises an axial force-to-rotary torque energy conversion apparatus. This apparatus also includes a translatable member and a rotatable member. A magnetic coupling is provided between the translatable member and the rotatable member for converting an axial force on the translatable member into a rotary torque on the rotatable member. The magnetic coupling can comprise a first permanent magnet associated with the translatable member and a second permanent magnet associated with the rotatable member. Each permanent magnet may be structured as interleaved, helical magnet sections of alternating polarities.
In another aspect, the invention comprises an actuator apparatus for a ventricle assist device (VAD) or a total artificial heart (TAH). The actuator apparatus includes a rotatable member and a translatable member. Drive means are provided for imparting rotary torque to the rotatable member, and a magnetic coupling converts rotary torque on the rotatable member to an axial force on the translatable member; the axial force on the translatable member being employed as a driver for the VAD or TAH. The magnetic coupling resides between the rotatable member and the translatable member.
In still another aspect, the invention consists of a total artificial heart (TAH) comprising a housing having a first ventricle and a second ventricle. A first diaphragm is coupled to the first ventricle for pumping blood therefrom when actuated towards the housing, while a second diaphragm is coupled to the second ventricle for similarly pumping blood therefrom when actuated towards the housing. The TAH also includes an actuator for actuating at least one diaphragm of the first diaphragm and the second diaphragm. The actuator includes a rotatable member and a translatable member, as well as drive means for imparting rotary torque to the rotatable member. A magnetic coupling is associated

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