Laparoskopik cerrahide akıllı eyleyicili ameliyat aletlerinin tutucu kuvvet kontrolü ve doku ile etkileşmi
Grasping force control and tissue interaction of smart actuated surgical tools in laparoscopic surgery
Yazar: MİTHAT CAN ÖZİN
Danışman: DOÇ. DR. İLKER MURAT KOÇ ; DR. ÖĞR. ÜYESİ BİLSAY SÜMER
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Sistem Dinamiği ve Kontrol Bilim Dalı
Derece: Yüksek Lisans, 2018
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Laparoskopik ameliyatların gerçekleşme süresi, çeşitli uçları olan ve uzun bir mile sahip ameliyat aletleri kullanıldığından dolayı açık ameliyatlara göre daha uzundur ve cerrahın el hissiyatında azalma meydana gelmektedir. Ameliyat sırasında cerrahın el hissiyatının azalmasından ve de ameliyat süresince el yorgunluğunun artmasından dolayı dokuya uygulanan fazla bastırma kuvveti ve ameliyat aletinin doku üzerinde kayması doku zedelenmesine sebebiyet vermektedir. Tutucunun dokuya uyguladığı bölgesel basma kuvvetinin direk ölçülebilmesi ve net kuvvettin hesaplanabilmesi doku zedelenmesinin engellenebilmesi için gereklidir. Bu tez çalışmasında şekil hafızalı alaşımlı (ŞHAlı) bir eyleyici ile beraber laparoskopik aletin ucuna yerleştirilen bir dokunsal algılayıcı sayesinde doku-ameliyat aleti etkileşimi incelenmiş olup basma ve kayma sırasındaki doku zedelenmesine neden olan kuvvetler araştırılmıştır. Dokunsal algılayıcı entegrasyonunun tutucu-doku etkileşimine olan etkisi belirlenmiştir. Dokunsal algılayıcıdan ve milden alınan geribildirimle kuvvet kontrolü sağlanarak doku zedelenmesinin minimuma indirilebileceği ve cerrahın el hissiyatının geri kazandırılabileceği gösterilmiştir. 

Laparoskopik ameliyat aletleri tutma, kesme, yakma vb. işlevlere sahiptir ve her işlev için ona uygun bir uç tasarımı mevcuttur. Laparoskopik tutucu uçları dişli ve ya düz olacak şekilde tasarlanmışlardır. Laparoskopik ameliyat aletleri el tutma yeri ve uç kısmı ile bunları birleştiren 30-40 mm uzunluğundaki bir milden oluşmaktadır. El tutma yeri de uç kısım gibi farklı şekillerde olabilmektedir. Geleneksel cihazlarda el tutma yeri ve uç kaldıraç mekanizması ile birbirine bağlıdır ve cerrahın el kuvvetiyle açılıp kapanır. Uzun ameliyatlar cerrahlarda el yorgunluğuna neden olmaktadır. Bu sorunun üstesinden gelebilmek için şekil hafızalı alaşımdan yapılmış bir eyleyici tasarlanmıştır. Bu eyleyici elektrik enerjisiyle tahrik edilmekte ve cerrah tarafından bir düğme ile kontrol edilebilmektedir. Bu sayede cerrahın eli tarafından uygulanması gereken mekanik enerji azaltılmış olup cerrahın el yorgunluğunun da azaltılması hedeflenmiştir. 

Tez çalışmasının sonunda laparoskopik ameliyat için akıllı eyleyiciye ve özel algılayıcıya sahip yenilikçi laparoskopik tutucu tasarlanmıştır. Geleneksel kaldıraç mekanizması kaldırılarak onun yerine nikel-titanyum malzemeden üretilmiş şekil hafızalı tel eyleyici olarak kullanılmıştır. Elektrik enerjisi kullanılarak ısıtılan  ŞHA tel kısalmakta ve tutucu ucun kapanmasını sağlamaktadır. Bu akıllı eyleyicinin kısalıp-uzaması sürücü devresi, tetik sistemi ve ya bilgisayar ile kontrol edilmiştir. Uca göre tasarlanmış olan algılayıcı sayesinde direk olarak kuvvet ölçümü yapılmış ve tutma kuvvetinin kontrolü sağlanmıştır. Bu dokunsal algılayıcı ince film katmanlardan oluşmaktadır ve piezoresistif özelliğe sahiptir. Uygulanan basma kuvvetinin etkisiyle sensörün direnci değişmekte ve kuvvet ölçümü mümkün olabilmektedir. Piezoelektrik ve kapasitif olmak üzere başka tip dokunsal algılayıcılar da mevcuttur. 8x4 algılama hücresine (taxele) sahip Piezoresistif bir dokunsal algılayıcı laparoskopik tutucuya uygun olacak şekilde imal edilmiştir. Bu algılayıcı 32 noktadan tutucu ucun dokuya uyguladığı bölgesel kuvveti ölçebilmektedir. Bu bölgesel kuvvetler haritalandırılmış, net kuvvet ve kuvvet merkezi hesaplanmıştır. Basma kuvveti geribildirim olarak kullanılarak tutma kuvvetinin gerçek zamanlı kontrolü yapılmış ve net tutma kuvvetinin eşik değeri olan 2 N'u aşmaması sağlanmıştır. Labview ortamında yazılmış olan programlarla oransal-integral-türevsel (PID) kontrol uygulanmıştır.

Abstract:
The aim of this study is to design an innovative laparoscopic surgical instrument using a smart actuator owing to shape memory alloy (SMA) and a tactile sensor that measures the magnitude of the tactile force of the touch.


The reason of this study is to solve the two main problems encountered in laparoscopic surgery. These problems are the hand-tiredness and tissue damage caused by excessive force of the surgeon.


Laparoscopic surgeries are more common than open surgeries. In laparoscopic surgery, surgical instruments with various tips and long shaft are used. The opening and closing motion of these instruments are performed by the hand of the surgeon from the hand holding place. Long surgeries cause hand fatigue in surgeons. In order to overcome this problem, an actuator made of shape memory alloy is designed. This actuator is driven by electrical energy and is controlled by a surgeon with a button. In this way, the mechanical energy required to be applied by the hand of the surgeon is reduced. Thus, the hand fatigue of surgeon is minimized.


Laparoscopic surgical instruments include holding, cutting, burning, etc. functions and have an appropriate tip design for each function. The laparoscopic holder tips are designed to be threaded or flat. The laparoscopic surgical instruments consist of a hand grip, a tip, and a 30-40 mm long shaft which connects them. The hand grip can also be in different shapes for the ergonomy. In conventional devices, it is linked to the hand grip and tip lever mechanism and is opened and closed by the hand of the surgeon.


Excessive force applied to the tissue due to the reduced hand feeling of the surgeon during the operation, the increased hand fatigue during the operation, and the shift of the surgical instrument over the tissue causes tissue damage. A tactile sensor and a tactile sensor integrated to the tip of the laparoscopic instrument together with a smart actuator is designed and the tissue-surgical instrument (tip) interaction is examined, the forces that may cause tissue damage during compression and slippage is determined. It is possible to prevent tissue damage by providing force control by feedback from the tactile sensor or from the shaft of the tool.


In this thesis, an innovative laparoscopic tool with smart actuator and custom tactile sensor for laparoscopic surgery is revealed. The traditional lever mechanism is removed and the shape memory alloy wire produced from nickel-titanium material is used as an actuator. The wire which is activated by electric energy, heats up and shortens. Thus, the tip of the tool is closed. This smart actuator is controlled by the computer with a custom amplifier circuit. The aim of this is to reduce the hand fatigue of the surgeon.


The tactile sensor will be placed at the end-effector of the tool which is the tip. This tactile sensor consists of thin film layers and is piezoresistive.  With the effect of applied pressure, the resistance of the sensor changes and force measurement is possible. Other types of tactile sensors are available, including piezoelectric and capacitive. By means of the sensor designed according to tip, force measurement is done directly at tip and control of the pinch force minimized the possible tissue damage.

This thesis includes five section which are, the introduction, the measurement of pinch force by distributed pressure measurement, the investigation of friction force, the design of the smart actuator and force control and the results.

In the first section, a brief introduction of laparoscopic surgery and the tools are given. Available measurement techniques in laparoscopic surgery and quantities that need to be measured are explained. The resultant forces and subforces are introduced. It is followed by the presentation of the smart materials and finally, the reason of the thesis is proposed.

In the second section, the characterization of the compression mechanism in the tool-tissue interaction is achieved by a tactile sensor integrated laparoscopic grasper. The main objective is to investigate and examine the total compressive force and local pressure distribution during a laparoscopic operation under ex-vivo experimental conditions. In this section a flat-tipped holder is used. Thus, the effect of the teeth on the  tip is eliminated. First, the tactile sensor with 32 measuring points (taxel) is designed to fit the tip of the holder. The sensitivity of the tactile sensor and the measurement range are set according to the target force range (0-4 N) of the holder-tissue interaction. The tactile sensor is manufactured using screen printing techniques. Because of the robust and reproducible properties, piezoresistive measurement method is chosen. After the integration of the tactile sensor, polymers such as polydimethylsiloxane (PDMS) and silicone rubber have been used to test and verify the measurement capability of the tactile sensor on viscoelastic materials. Finally, an ex-vivo experiment is conducted on chicken liver and poultry to examine the soft tissue-tool interaction during the closure movement of the laparoscopic holder.

In the third section, the forces during laparoscopic grasping is investigated in a flat-ended laparoscopic grasper in ex-vivo experiments. Push, pull and shaft forces are the forces that must be measured to calculate the friction force between the tip and the tissue. The pulling force while holding an elastic tissue causes the elastic deformation firstly, followed by the friction between the tissue and the tip. Additionally, adhesive effects are seen during opening of the tip of the grasper. The magnitude of the adhesive forces is compared with the pinch and pull forces during an ex-vivo grasp. The section is organized as follows: the methodology of the tests, the adhesive force tests and the friction force tests.

In the forth section, the design smart actuator which replaces shaft of the  laparoscopic grasper is given.  One piece of shape memory alloy wire and the antagonist spring will be used as actuator in order to open and close the tip. The actuator is approximately 35 cm in length and 15 mm in diameter. The actuator is designed will apply a force of up to 20 N. A custom driver circuit is produced to activate the actuator by control signals from a computer. According to the output signal coming from the computer, the circuit board uses metal oxide semiconductor field effect transistors (MOSFETs) and bipolar junction transistors (BJTs) to amplify the signal. It has a power supply of 20 V and 3 A. The current passes over shape memory alloy wire which heats and shortens the wire, is controlled. A proportional-integral-derivative (PID) controller is designed in LabVIEW. In order to increase the opening speed of the tip, it is necessary to cool the wire with air. Air cooling holes is opened on the shaft so that the air can be evacuated. Cooling air is supplied into the shaft at various pressure values, and the effect of cooling on overshoot and settling time during force control is examined. 


In the final section, results of the all sections are discussed. The results of the study are given below respectively to the sections:


The interaction of the laparoscopic grasper with soft materials was investigated by measuring pressure distribution by using a tactile sensor in ex-vivo experimental conditions. The tactile sensor incorporates a flat-tipped laparoscopic grasper that opens and closes angularly. The closure of the tip causes an unbalanced pressure distribution over the specimens. To characterize the mechanics of the soft material between the tip and the tissue, the local pinch forces and the total pinch force and center of pressure position are measured in the different types of samples. As a result, pressure distribution measurement contributes to increase tactile sensation of surgeon in the laparoscopic surgery. In experiments on chicken liver and meat, local forces are  distributed homogeneously over a larger contact area than polymer samples. It is seen that the total force is about 0.7 N. It is shown that controlling the position of the center of pressure, i.e. the total force, and the magnitude of the force, help to prevent tissue trauma during a laparoscopic operation, and improves surgical operations.


The adhesion force and friction coefficient associated with the friction force of the flat-tipped laparoscopic holder were evaluated in terms of prevention of slippage and providing safe grasp in ex-vivo experiments with chicken meat samples. Two experimental setups which are the friction test setup and the laparoscopic grasper test setup, were designed to evaluate the friction and adhesive behavior of the laparoscopic tool with/out tactile sensor. The tactile sensor at the tip gives better results than the load cell  at the shaft for the measurement of the pinch force due to its measurement position. Calculation of the pinch force from the shaft force measurement is less efficient due to the change in the force / pressure center and the requirement of force transfer ratio. The addition of a tactile sensor in the measurement of the coefficient of friction has negligible effect. It is possible to estimate the friction force between the tip and the tissue by using the tactile sensor with experimentally measured friction coefficients. In this study, the measured coefficient of friction (mean) between the tip and tissue in the ex-vivo experiment of chicken meat is 0.3. Laparoscopic grasper equipped with a tactile sensor that provides direct measurement of the pinch force and an estimation of the friction force are suitable for training of novice surgeons. The adhesive forces measured in the adhesion test are less than half of the minimum friction force and less than a quarter of the minimum pinch force. The integration of the tactile sensor increases the adhesive forces by 44\% on average. However, the measurement of the contact area and the stress for the examination of tissue trauma will give better results than the measurement of the magnitudes of the adhesive forces.


A smart actuator is designed to reduce surgeon's hand fatigue. This smart actuator has a shape memory alloy. The designed actuator has active cooling and allows the tip to be fully opened and closed. It is thought that the surgeon can reduce hand fatigue because it works with electrical energy. To reduce tissue damage, the actuator force was controlled by a PID controller, and the effect of the cooling on the actuator performance was examined as the amount of overshoot and the settling time. Effect of the cooling system is determined that overshoot is reduced by 3\% and the settling time is shortened up to approximately 29\%.