Ankilozan spondilit hastaları için hareketli yatak tasarımı
Mechanical bed design for ankylosing spondylitis patients
Yazar: HAMZA TOKLU
Danışman: DR. ÖĞR. ÜYESİ VEDAT TEMİZ
İstanbul Teknik Üniversitesi / Lisansüstü Eğitim Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Konstrüksiyon Bilim Dalı
Derece: Yüksek Lisans, 2021
Konu: Makine Mühendisliği = Mechanical Engineering ; Romatoloji = Rheumatology
Dizin: Spondilit-ankilozan = Spondylitis-ankylosing

Özet:
Ankilozan spondilit (AS) genellikle eksenel iskeleti etkileyen karakteristik yangılı bel ve sırt ağrılarına sebep olan kronik, ilerleyici, iltihaplı bir romatizma hastalığıdır. AS hastalığının ortaya çıkmasında genetiğin etkisi rol oynamaktadır ve genellikle yirmili ve otuzlu yaşlarda ortaya çıkar. Prevalansı %0.1 ile %1.4 arasında bölgeden bölgeye değişiklik göstermektedir. Hastalığın karakteristik özelliği dinlenmeyle artan egzersizle hafifleyen yangılı ağrılardır. Bu durum sabah uyanıldığında ağrılara ve tutukluklara sebep olur. AS yangılı ağrıların yanı sıra eksenel iskelette hareket kısıtına yol açan radyolojik değişikliklere sebep olur. AS'in ilerleyen evrelerinde hastanın omurları birleşerek "bambu kamışı omurga" denilen yapıyı alabilir. Tedavi yöntemleri ilk kademede nonsteroid antiinflamatuar ilaçlarken ilerleyen evrelerde kortikosteroidler, hastalığı modifiye eden anti romatizmal ilaçlar, anti tümör nekroz faktör-alfa gibi tedaviler uygulanabilir. Ankilozan spondilit tedavisinde fizyoterapi oldukça önemli bir yer tutar. Ağrıların egzersizle azalan karakteristikte olması sebebiyle hastaların fiziksel olarak aktif bir yaşam sürmesi önemlidir.
Hastalığın gece boyunca ağrılara sebep olması ve uyku kalitesini düşürmesi gece hastayı uyandırmadan hareket ettirecek bir yatağın ağrılara ve uyku kalitesine etkisini merak ettirmektedir. Yapılan bu çalışmada konstrüktif geliştirme sürecinden geçirilerek ankilozan spondilit hastaları için hareketli bir yatak tasarımı yapılmıştır. Ürün fikrinin ortaya çıkmasından sonra istekler listesi oluşturulmuş, bu isteklerden ödev tanımı kesinleştirilmiştir. Sezgisel çözüm arama yöntemlerinden "Galeri Metodu" seçilmiş ve uygulanmıştır. Toplanan çözümlerin sayısının azaltılması için "Biner Tablo" yöntemi kullanılmış ve kalan çözümler için bir fayda değer analizi yapılmıştır. Karar kılınan çözüm standart tek kişilik bir yatağın enine bölümlenmesi ve her bir bölmesinin bağımsız olarak yukarı aşağı hareket kabiliyetine sahip olmasıdır. Yatak parametrelerinin belirlenmesinde antropometrik ölçümlerden ve ankilozan spondilit hastaları için önerilen egzersiz hareketlerinden yararlanılmış ve yatak enine yedi parçaya bölünmüştür. Hastaya verilmesi istenen temel hareket lomber ekstansiyon olarak belirlenmiştir. Ankilozan spondilit hastalarının eklem hareket açıklıkları incelenmiş ve yatak bölmelerinin hareket miktarları belirlenmiştir. Hareket mekanizması olarak çeşitli alternatifler değerlendirilmiş ve kam-makara mekanizmasında karar kılınmıştır. Kamlar ve milin hesapları gerçekleştirilmiş, tahrik ve hız-moment dönüşümü için redüktör ve motor seçilmiştir. Verilmek istenen hareketin hastanın ağır uyku evresinde olması için uyku evreleri incelenmiştir. Ana fonksiyon taşıyıcı elemanı tasarlandıktan sonra yardımcı elemanların tasarımına geçilmiştir. Hazır baza iskeleti yatak iskeleti olarak kullanılmış ve mekanizma bu iskeletin içine yerleştirilmiştir. Bölmelere ayrılmış ahşap levhalar kılavuzlarla iskelete tespit edilmiştir. Yatak süngeri olarak verilen harekete uyum sağlayabilecek lazer kesim bir sünger kullanılmış ve yatak tasarımı tamamlanmıştır.

Abstract:
Ankylosing spondylitis (AS) is a progressive, chronic, inflammatory rheumatologic disease that mainly affects the sacroiliac joints and the axial skeleton. AS is a prototype of a disease group called spondyloarthropathy. Etiology of ankylosing spondylitis is not fully understood but genetics play a major role in spondyloarthropathy. HLA-B27 gene is associated with ankylosing spondylitis. Diagnosis of AS is made with Modified New York Criteria.
AS disease onset generally occurs in the second or third decade of life. Prevalence of ankylosing spondylitis is %0.1 and %1.4 and varies between regions. AS is also seen approximately two to three times more in men than women. Disease pattern is also different for men and women. In men, disease affects mainly the spine and pelvis but in women, involvements in hips, pelvis and knees are seen more often. Disease activity is measured with the Bath Indices such as the BASDAI, BASFI and BASMI. There are other indices to measure different outcomes of the disease.
In early phases, disease affects sacroiliac joints while in later stages it may also affect the axial skeleton. AS causes chronic inflammatory pain and stiffness. Pain in the hips and lower back that accompanies morning stiffness is one of the earliest symptoms of AS. The characteristic of the inflammatory pain of AS is that it reduces with activity and returns with inactivity. Pain is generally more severe at night. Also, AS causes radiological changes in the spine where the range of motion is limited as the disease progresses. Furthermore, the bones in the spine might fuse together in advanced stages of the disease and become bamboo-shaped. These symptoms cause difficulties for the patient, reduces the quality of sleep and the quality of life. Fatigue and anxiety are seen more among AS patients.
Treatment of AS is recommended as a combination of both pharmacological treatments and physiotherapy. Several options for pharmacological drugs exist for treating AS such as nonsteroidal antiinflammatory drugs, corticosteroids and DMARDs, and anti-TNF-a treatments. Also, physiotherapy plays an important role in treating AS. The purpose of physiotherapy is to limit the advancement of the disease and maintain the range of motion and also alleviating inflammatory pains.
The characteristic back pain that reduces with activity and returns with inactivity causes morning stiffness and pain in patients. This results in poor sleep and reduced functionality. Possible effects of a mechanically moving bed during sleep on the quality of sleep, morning stiffness and pain in ankylosing spondylitis patients is not known. The aim of this study is to design such a bed through a systematic approach of engineering design.
With the idea of the product available, a requirements list was made by identifying the needs of the patients and examining external limitations. The requirements list was then abstracted to identify the essential problem and then the task is defined.
Since this is a new design, a conventional search for a solution such as information gathering, analysis of natural systems, analysis of existing technical systems, etc. was unsuitable and therefore not used. Intuitive solution finding methods were examined. A search for a conceptual design was made using the "Gallery Method". Gallery Method is an idea generation technique in a group, developed by Hellfritz. A total of fifteen ideas were collected with two separate instances of employing the method. These ideas can be roughly grouped into dividing the bed into a grid and controlling the individual parts to move the patient, an inflatable and deflatable sections on the bed, dividing the bed into mechanically moved sections each independent from each other, an external arm that can move the patient, a mechanism under the bed that can massage and move the patient and conveyor like mechanism that can individually move separate parts of the body. These solution variants were first narrowed down using a binary method with using not disturbing sleep, wide range of motion, low noise levels, cost and weight criterias. The remaining five ideas were subjected to a cost-benefit analysis. Not disturbing sleep, wide range of motion, safety and lightness & cheapness were used as weighed evaluation criterias. The solution with the best overall value was dividing the bed into several transverse sections and controlling each individual section to move the patient.
For determining the number of individual segments, anthropological measurements of adults were inspected. The recommended exercises for ankylosing spondylitis patients were also taken into consideration. As a result, a recommended exercise and a feasible candidate for a movement called "lumbar extension" were selected. This resulted in dividing the bed into seven segments, the center one of which lines up with the waist. Upper segments were lined up with the torso and the head. The range of motion of lumbar extension in ankylosing spondylitis patients determined the ranges of motion of the segments. This intended movement is called "trunk lateral bending" when lying sideways and "lumbar flexion" when lying prone both of which the range of motion is greater than lumbar extension.
In a study that estimated anthropometric measurements of Turkish adults, a mean of 97 kilograms with a standard deviation of 12 kilograms was given for weight measurement. Mean plus one sigma that was rounded up to 110 kilograms were therefore used for design weight. 1,25 factor of safety was used during calculations. For calculating the loads acting on the individual bed segments, weight percentages of body segments were inspected. This showed heavier loads acting on the torso and the hip segment of the bed.
Several options were reviewed before selecting the drive mechanism of the bed. Linear actuators are a direct candidate for providing linear motion. They are however costly and require a controller to control the speed. Slider-crank mechanisms turn rotational motion into linear motion however the design of a crankshaft is complex and costly. Scissor lifts were another mechanism that can be adapted into lifting a bed segment however each bed segment requiring a relatively heavy lift mechanism, inability to have periodic movement without reversing the direction of rotation, low efficiency of power screws makes this solution inadequate. Screw jacks were another candidate for a drive solution however screw jacks are generally designed for much larger loads and therefore unsuitable. Rack-pinion mechanisms are generally used for driving linear motion however inability to have periodic motion without reversing the direction of rotation and the difficulty of protecting the gear from external dust and dirt, keeping the gears oiled makes this solution unsuitable. Cam mechanisms are generally used for turning rotational motion into linear follower motion. There are many types of cams for different purposes. For this task, the relatively small movement of the bed segments, the ability to have periodic movements of the segments without reversing the direction of motion, low friction losses and low cost makes this mechanism suitable.
For the cam profile optimization, a software package is used. Cam shape is the main property of the cam. Different movement options of bed segments resulted in different cam segments that are optimized. Basic diameter was optimized by selecting different diameters for the same inputs, cam width, roller diameter, roller width, motion functions, strength calculations were optimized as well. For the cam material, steel was too heavy and engineering polymer cast polyamide was used instead. For rotational speed 1 to 6 rpm's were considered.
Shaft design was made using a software package. Different number of bearings and diameters were considered with stresses and deflections in mind.
For the gearbox, worm gears were selected since only the worm gear offers such large reduction ratios in a small package. The gearbox is selected from a company called "Yılmaz Redüktör" and is coupled with a brushless DC motor that can run on a regular power outlet with an AC-DC power supply converter.
The bed frame that consists of square profiles welded together was selected from a manufacturer and since the material allows welding the required alterations to the frame to fit the mechanism inside could be made. Guiding of the up and down motion of the bed segments was made with linear bearings on the side of the bed frame.
The time control of the motor can be made using the controller of the DC motor and the motion can be applied to the bed only when the patient is approximately in the deep sleep phase to reduce the chance of waking up.
With the new design of a mechanical bed for ankylosing spondylitis patients, it is hoped to see an improvement in the morning pains and stiffness and the quality of sleep.