AU2021101677A4

AU2021101677A4 - A device and method for controlling magnetically levitated heart assist device

Info

Publication number: AU2021101677A4
Application number: AU2021101677A
Authority: AU
Inventors: Souvik Ganguli; Anurag Sohane; Swati Sondhi
Original assignee: Individual
Current assignee: Individual
Priority date: 2021-03-31
Filing date: 2021-03-31
Publication date: 2021-07-01
Anticipated expiration: 2029-03-31

Abstract

The present disclosure relates to a device and a method for controlling a magnetically levitated heart assist device.The device includesthe development of a lower-order prototype model for converting a higher-order unstable system into a stable one using a random weight based pole shifting method;wherein the stable system is reduced in a lower-order model using slime mould technique;wherein time and frequency domain parameters of the lower-order model is preserved in line with the original system model;wherein integral of square error (ISE) as an error function is selected to measure unknown lower-order model parameters using a pseudo-random binary sequence as an unbiased input signal. A fractional-order PID controller operated using Arduino UNO serves asa controlling unit for controlling the operation of the unstable system used as a heart assist device. 16 100 Lower-order prototypemodel102 FOPIDcontroller104 Figure1 200 converting a higher-order unstable systeminto a stable one using a rardorn weight-based pole s hifting method 202 reducing the stablesystem using slime mouldtechnique to generate a lower-order model preserving time andfrequency domain parameters of the lower-order model in line with theorigiral system model 208 choosingintegral ofsquare error (ISE) as an error funtion to measure unknown lower-order model parametersusr a pseudo-random binarysequence as an unblasedinput signal Figure 2

Description

Lower-order prototypemodel102 FOPIDcontroller104

Figure1

200

converting a higher-order unstable systeminto a stable one using a rardorn weight-based pole s hifting method 202

reducing the stablesystem using slime mouldtechnique to generate a lower-order model

preserving time andfrequency domain parameters of the lower-order model inline with theorigiral system model

208 choosingintegral ofsquare error (ISE) as an error funtion to measure unknown lower-order model parametersusr a pseudo-random binarysequence as an unblasedinput signal

Figure 2

ADEVICE AND METHOD FOR CONTROLLING MAGNETICALLY LEVITATED HEART ASSIST DEVICE FIELD OF THE INVENTION

The present disclosure relates to a device and a method for controlling a magnetically levitated heart assist device.

BACKGROUND OF THE INVENTION

Congestive heart failure continues to be a leading cause of morbidity and mortality around the world, and heart transplantation, the only approved treatment for serious cases of the condition, is unable to keep up with the high demand. Left ventricular assist devices (LVADs) are an emerging treatment for thousands of patients suffering from end-stage heart disease. These "artificial hearts" are implanted and work with the natural heart to pump blood. The second-generation pumps were the rotary pumps that use the blood as a lubricant in fluid film bearings. The third generation of pumps in commercial research laboratories was developed using feedback-controlled magnetic levitated pump impellers.

Magnetic levitation eliminates mechanical wear and shear damage to the blood (red blood cells, platelets, and leucocytes). Motivated by these magnetic levitation benefits, the first magnetic levitation pump was introduced in an animal test at the University of Pittsburgh in 1998. The technology was facilitated by feedback control, advancements in magnetic materials and the systematic optimization of the controlled plant. However, the small size, short time constants, non-linearity, instability, and quasi-periodic disturbances of the natural heart pose a major challenge to control engineers. As a result, a complete experimental apparatus was developed to study the levitation system in these artificial hearts for power consumption and control. The experimental Maglev plant had one active degree of freedom (DOF)-an axial direction with complete magnetic levitation. It was compact and presented an excellent laboratory base for maglev and artificial heart experiments. The use of linear voice coil actuators for axial displacement and not purely passive radial levitation was a unique aspect of the design. The apparatus had a faster time constant similar to Maglev's LVADs in commercial development. However, it's modelling such a system results in an unstable system which is difficult and often challenging to control. Thus, we have taken up the model reduction of an existing unstable system that has a real-life application in the field of biomedical engineering, especially in artificial heart pumps. This unstable system represents the model of the magnetically levitated apparatus in the left ventricular heart assist device (LVAD).

The common procedure adopted for the reduction of unstable plant models is to separate the stable and unstable parts. The stable part is reduced without disturbing the unstable part. The unstable part is then added to the reduced model to constitute the final plant model. This approach fails if there are only unstable poles in the system because the unstable system cannot be reduced solely. Some researchers have opted for the pole shifting method as a means to develop new reduction techniques. Few researchers have explored an arbitrary shift to achieve stability in a system to reduce it further. Others have taken up the idea to obtain the mean of the real part of the poles as a means to encourage pole shifting strategy. Since harmonic mean was found to be the least among harmonic, geometric and arithmetic means, hence it is quite obvious to be the popular choice. Ganguli et al. opted for a slight deviation from the above introducing the concept of weighted harmonic mean to achieve the reduction process. But the choice of the weights was arbitrary.

In one solution, a miniature pulsatile implantable ventricular assist device and method for controlling a ventricular assist device is disclosed. A pumping system to assist the ventricle in either or both of the heart. In one embodiment, a separate device is provided for each ventricle. In another embodiment, one device provides both left and right pumping. The pumping system is small, efficient, atraumatic and fully implantable. The ventricular assist device comprises an actuator plate between a pair of serially connected pumping chambers that operate in a two-stroke mode, particularly a power stroke and a transfer stroke. Ventricular assist devices regulate pump pressure by means of current through an electromagnet. In the pumping system, the spring provides a "spring force" on the actuator plate that faces the high-pressure pump chamber. The biasing force allows the spring to store and supply energy from the electromagnetic drive system to make better use of the pump components and reduce the size of the pump and reduce power consumption.

In another solution, a magnetically levitated and driven blood pump is disclosed. A device for pumping blood, includes a housing having a distal end adapted to be coupled to a catheter , a proximal end having an outlet , and a tubular body extending between the distal and proximal ends along an axis. A rotor is rotatably disposed within the housing . A first magnetic bearing is operative to levitate the rotor along the axis within the housing . A second magnetic bearing controls the rotational frequency of the rotor . A third magnetic bearing controls a radial position of the rotor .

Yet in another solution, an organ assist system and method is disclosed. An organ assist system having a closed fluid system having a ring-shaped prosthetic contactively surrounding at least a portion of a body part, including bladders adapted for selectable dilation and contraction in response to varying fluid pressure therewithin, a fluid pump, and apparatus for pressurizing the bladders; and a control unit for controlling operation of at least the fluid pump; pressure sensors within the fluid system; a power source, and shut off valves. The pressurization apparatus includes pressure cells arranged in an array, each pressure cell having a shut-off valve at its inlet, and a shut-off valve at its outlet, the shut-off valves being controlled by the control unit such that the pressurization apparatus is operable to provide a range of pressurizations to the bladders of the prosthetic for applying a controlled variable pressurizing effect to the body part thereby.

To overcome the aforementioned drawbacks, there exists a need to develop a device and method for controlling magnetically levitated heart assist device. SUMMARY OF THE INVENTION

The present disclosureseeks to providea device and a method for controlling magnetically levitated heart assist device for improvising settling time and rise time.

In an embodiment, a device for controlling magnetically levitated heart assist deviceis disclosed. The device comprises:

a fractional-order PID (FOPID) controller to control the unstable system dynamics of a magnetically levitated heart assist device wherein higher-order unstable system into a stable one using a random weight-based pole shifting method wherein the higher-order stable system is reduced in a lower-order model using slime mould technique; wherein time and frequency domain parameters of the lower-order model is preserved in line with the original system model; wherein integral of square error (ISE) as an error function is selected to measure unknown lower-order model parameters using a pseudo-random binary sequence as an unbiased input signal; and a FOPID controller-based controlling unit for controlling the operation of the unstable plant model.

In an embodiment, the device for the lower-order model is developed with the combination of operational amplifiers, resistors and capacitors.

In an embodiment,steps for controlling the operation of the FOPID controller comprises:

generating pulse width modulation for plant input upon connecting digital pin of the controlling unit; receiving analog signal input from the output of the plant through an analog pin; and wherein analog pin behaves as the reference input from the potentiometer. In an embodiment, the output of the plant is an input for the analog pin. In an embodiment, unknown parameters of the controller are optimized with the help of the slime mould technique.

In another embodiment, a method for controlling magnetically levitated heart assist deviceis disclosed. The method comprises:

converting a higher-order unstable system into a stable one using a random weight-based pole shifting method; reducing the stable system using slime mould technique to generate a lower-order model; preserving time and frequency domain parameters of the lower order model in line with the original system model; and choosing integral of square error (ISE) as an error function to measure unknown lower-order model parameters using a pseudo-random binary sequence as an unbiased input signal.

In an embodiment, the reduction process employs the optimization technique to assign certain constraints to accommodate the stability, minimum phase and dc gain features.

In an embodiment, random weights are used to achieve the pole shifting by imposing two constraints, wherein the two constraints are a) the sum of the weights must be less than unity and b) the weighted geometric mean must be less than or equal to the original geometric mean. In an embodiment, the time and frequency domain parameters of the reduction method is preserved in line with the original system model. An objective of the present disclosure is to improvise settling time and rise time. Another object of the present disclosure is tostabilize the unstable plant model. Yet another object of the present invention is to deliver anexpeditious and cost-effective method for controlling magnetically levitated heart assist device.

To further clarify the advantages and features of the present disclosure, a more particular description of the invention will be rendered by reference to specific embodiments thereof, which is illustrated in the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope. The invention will be described and explained with additional specificity and detail with the accompanying drawings. BRIEF DESCRIPTION OF FIGURES

These and other features, aspects, and advantages of the present disclosure will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:

Figure lillustrates a block diagram of a device for controlling magnetically levitated heart assist deviceis disclosed in accordance with an embodiment of the present disclosure; and

Figure 2illustrates a flow chart of a method for controlling magnetically levitated heart assist deviceis disclosed in accordance with an embodiment of the present disclosure.

Further, skilled artisans will appreciate that elements in the drawings are illustrated for simplicity and may not have been necessarily been drawn to scale. For example, the flow charts illustrate the method in terms of the most prominent steps involved to help to improve understanding of aspects of the present disclosure. Furthermore, in terms of the construction of the device, one or more components of the device may have been represented in the drawings by conventional symbols, and the drawings may show only those specific details that are pertinent to understanding the embodiments of the present disclosure so as not to obscure the drawings with details that will be readily apparent to those of ordinary skill in the art having benefit of the description herein.

DETAILED DESCRIPTION

To promote an understanding of the principles of the invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated system, and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates.

It will be understood by those skilled in the art that the foregoing general description and the following detailed description are exemplary and explanatory of the invention and are not intended to be restrictive thereof.

Reference throughout this specification to "an aspect", "another aspect" or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present disclosure. Thus, appearances of the phrase "in an embodiment", "in another embodiment" and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment.

The terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process or method that comprises a list of steps does not include only those steps but may include other steps not expressly listed or inherent to such process or method. Similarly, one or more devices or sub-systems or elements or structures or components proceeded by "comprises...a" does not, without more constraints, preclude the existence of other devices or other sub-systems or other elements or other structures or other components or additional devices or additional sub-systems or additional elements or additional structures or additional components.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The system, methods, and examples provided herein are illustrative only and not intended to be limiting.

Embodiments of the present disclosure will be described below in detail with reference to the accompanying drawings.

Referring to Figure 1, a block diagram of a device for controlling magnetically levitated heart assist deviceis illustrated in accordance with an embodiment of the present disclosure.The device 102 includes the process for converting a higher-order unstable system into a stable one using a random weight-based pole shifting method. The control unit 104 is fractional-order PID (FOPID) controllerwhich consists of a sum of fractional operators along with controller gains.

In an embodiment, the FOPID controller 104 then controls the lower-order unstable system using an optimization technique such as slime mould technique. The slime mouldtechnique is a population-based optimization technique that is proposed based on the oscillation style of slime mould in nature. The slime mouldtechnique has an inimitable mathematical model that simulates positive and negative feedbacks of the propagation wave of slime mould. It has a dynamic structure with a stable balance between global and local search drifts.

In an embodiment, in the model 102 the time and frequency domain parameters of the lower-order model are preserved in line with the original system.

In an embodiment, the prototype model 102 thereafter selects integral of square error (ISE) as an error function to measure unknown lower-order model parameters using a pseudo-random binary sequence as an unbiased input signal. The pseudorandom binary sequence is a binary sequence that, while generated with a deterministic algorithm, is difficult to predict and exhibits statistical behaviour similar to a truly random sequence.

In an embodiment, the FOPID controlling unit/controller 104 is connected with the lower-order model 102 for controlling the unstable dynamics of the plant. The controlling unit 104 used in the device is Arduino UNO.The FOPID controller 104 can also be realized by the Raspberry-pi, NodeMCU and the like as per the requirement of the device.

In an embodiment, steps for controlling the operation of the FOPID controller 104 includes generating pulse width modulation for plant input upon connecting digital pin of the control unit. Then receiving analog signal input from the output of the plant through an analog pin. Analog pin behaves as the reference input from the potentiometer.

In an embodiment, the output of the plant is an input for the analog pin. In an embodiment, unknown parameters of the controller 104 are optimized with the help of the slime mould technique.

Figure 2 illustrates a flow chart of a method for controlling magnetically levitated heart assist deviceis disclosed in accordance with an embodiment of the present disclosure. At step 202, the method 200 includes converting a higher-order unstable system into a stable one using a random weight-based pole shifting method.

At step 204, the method 200 includes reducing the stable system using the slime mould technique to generate a lower-order model.Reduced-order models are simplifications of high-fidelity complex models.

At step 206, the method 200 includes preserving time and frequency domain parameters of the lower-order model in line with the original system model.

At step 208, the method 200 includes choosing the integral of square error (ISE) as an error function to measure unknown lower-order model parameters using a pseudo-random binary sequence as an unbiased input signal. Thes ystem model performance is measured by integrating the square of the system error over a fixed interval of time. This performance measure and its generalizations are frequently used in linear optimal control and estimation theory for measuring circuit experimental structures optimum value.

In an embodiment, random weights are used to achieve the pole shifting by imposing two constraints, wherein the two constraints are a) the sum of the weights must be less than unity and b) the weighted geometric mean must be less than or equal to the original geometric mean.

In an embodiment, the time and frequency domain parameters of the reduction method is preserved in line with the original system model.The FOPID controlling unit/ controller 104 has very good responses, particularly in terms of settling time and rise time. Thus the performance of the FOPID controller 104 is found to be quite satisfactory.

The drawings and the forgoing description give examples of embodiments. Those skilled in the art will appreciate that one or more of the described elements may well be combined into a single functional element. Alternatively, certain elements may be split into multiple functional elements. Elements from one embodiment may be added to another embodiment. For example, orders of processes described herein may be changed and are not limited to the manner described herein. Moreover, the actions of any flow diagram need not be implemented in the order shown; nor do all of the acts necessarily need to be performed. Also, those acts that are not dependent on other acts may be performed in parallel with the other acts. The scope of embodiments is by no means limited by these specific examples. Numerous variations, whether explicitly given in the specification or not, such as differences in structure, dimension, and use of material, are possible. The scope of embodiments is at least as broad as given by the following claims.

Benefits, other advantages, and solutions to problems have been described above with regard to specific embodiments. However, the benefits, advantages, solutions to problems and any component(s) that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as a critical, required, or essential feature or component of any or all the claims.

Claims

WE CLAIM

1. A method for controlling magnetically levitated heart assist device is disclosed. The method comprises of higher-order unstable system dynamics for a magnetically levitated heart assist device which is converted into a stable one using a random weight based pole shifting method; reducing the stable system using slime mould technique to generate a lower-order model; preserving time and frequency domain parameters of the lower-order model in line with the original system model; and choosing integral of square error (ISE) as an error function to measure unknown lower-order model parameters using a pseudo-random binary sequence as an unbiased input signal.

2. The method as claimed in claim 1, wherein the reduction process employs the optimization technique to assign certain constraints to accommodate the stability, minimum phase and dc gain features.

3. The method as claimed in claim 2, wherein random weights are used to achieve the pole shifting by imposing two constraints, wherein the two constraints are a) the sum of the weights must be less than unity and b) the weighted geometric mean must be less than or equal to the original geometric mean.

4. The method as claimed in claim 1, wherein the time and frequency domain parameters of the reduction method is preserved in line with the original system model.

5. A device for controlling magnetically levitated heart assist device, the device comprises: ageneral model reduction approachfor converting a higher order unstable system into a stable one using a random weight based pole shifting method; wherein the stable system is reduced in a lower-order model using slime mould technique; wherein time and frequency domain parameters of the lower order model is preserved in line with the original system model; wherein integral of square error (ISE) as an error function is selected to measure unknown lower-order model parameters using a pseudo-random binary sequence as an unbiased input signal; and a controlling unit for regulating the operation of the FOPID controller.

6. The device as claimed in claim 5, wherein the device for the lower-order model is developed with the combination of operational amplifiers, resistors and capacitors.

7. The device as claimed in claim 5, wherein steps for controlling the operation of the FOPID controller comprises:

generating pulse width modulation for plant input upon connecting digital pin of the controlling unit; receiving analog signal input from the output of the plant through an analog pin ; and wherein analog pin behaves as the reference input from the potentiometer.

8. The device as claimed in claim 7, wherein the output of the plant is an input for the analog pin.

9. The device as claimed in claim 5, wherein unknown parameters of the controller are optimized with the help of slime mould technique.