1. Deepak Chandran (A20336465)
Praveen S R (A20325931)
MMAE 445 : FINAL PROJECT REPORT
HYDRAULIC ARM SUPPORTER
BACKGROUND:
Field and Necessity of Invention:
The present invention is in the field of physiotherapy. More particularly, the present invention is in the
technical field of arm supporting devices. Paralysis is the inability of muscle or group of muscles to move on
their own. Often, signals from the brain don’t often get transmitted to the muscles after a stroke. With a
paretic arm, most patients find it difficult to perform some tasks like lifting his/her arm up which was
previously easy for the patient. The invention is designed to motivate the patient by giving support to a
person’s arm until he/she recovers, thereby helping regain senses in their arm.
Patients would require attendants to assist them to perform their regular activities. It would be challenging
for the person to perform these tasks themselves because either they lack the strength or they get
demotivated by presuming the task would be daunting. Some of the tasks may include lifting a coffee mug, or
spoon for their daily meal, pick and place any objects from a table, painting etc. We understand this
requirement for these patients and focus on providing a hydraulic force to aid the arm in lifting the objects
which could be manually controlled by the patients.
The concept and the design of this device was created keeping in mind the patients affected due to stroke. But
by not limiting the benefits it offers, it can be used by any patient or anyone who has difficulty in producing a
motion to his/her arm and needs some kind of support. Though the idea was thought keeping in mind
patients suffering from stoke, under proper guidance and understanding its applications it can be used by any
person who finds it useful.
Description of the Prior Art:
While the prior art shows a number of arrangements for supporting a person's arm during medical treatment
such as the contoured arm board disclosed in Hazelwood et al. U.S. Pat. No. 3,295,518 (1968) which shows an
adjustable leg rest which may be used to support a person's arm or leg during healing and U.S. Pat. No.
4265232 A (1981) which shows ram type arm contour device to support the patients arm, no manual device
has been found which specifically pioneers motion of arm supporter controlled with hydraulic telescopic
actuators that can be mounted on a table or a wheel chair with special arrangements.
In view of the originality of our invention, we strongly argue that our product is more advantageous over
existing manual arm supporters in physiotherapy centers/ hospitals. We use hydraulic pressure instead of
mechanical linkages which self-sustaining in any position of the arm supporter. Our arm supporter
additionally motivates the patient by eliminating the dependency of attendants. As a result, the rehabilitation
process enhances.
The device primarily provides some exercise to stimulate their senses back into their paralyzed arm by
motivating patients to do their regular activities like lifting a spoon, a pen, painting etc. until they recover
completely. This portable, light-weight hydraulic arm supporter provides stroke victims to prop his arm at an
inclined position to prevent the accumulation of fluids in the hand and wrist area. Arm support surface has a
concave contour to comfortably receive a person's arm and includes elastic straps for holding the arm
securely in position. Everyday use of this device provides therapy by expanding and contracting the
forearm muscles, strengthening wrist joints and regulation of blood flow into the paretic arm
2. DESCRIPTION OF INVENTION:
Features of the Device:
The main components of the device are actuator- Fig (1), arm supporter- Fig (2), wrist pad- Fig (5),
piston and syringe arrangement Fig -(4 and 3), Inter connecting pipe Fig (7), base clamp-Fig (6), L
pin- Fig (8), tube connector- Fig (9). Nuts and bolts are standard items which are not depicted in the
exploded view.
The device is anchored in a special wooden table used specifically for this device with the help of nut
and bolt arrangement from the actuator.
The actuator Fig (1) is connected to arm supporter Fig (2) with the help of l-pin Fig(8)
The front end of the arm supporter Fig (2) consists of a threaded rod projecting downwards which
can be clamped to the wrist pad Fig (5) using nut as shown in Fig (9). This arrangement is
incorporated to accommodate the varying arm length of different patients.
The rear end of the arm supporter Fig (2) is connected to a base clamp Fig (6) to arrest the motion
and acts as a pivot for attaining crank motion of Fig (2).
The bottom most part of Fig (1) is connected to Fig (4 and 3) using Fig (7).
The arm supporter Fig (2) has provision for clamps to which elastic straps are connected.
All parts have rounded edges to ensure safety to the operating personnel.
Operation of the device:
The Patient (or any person using the device) rests his arm on arm supporter Fig (2) and his arm is
strapped using an elastic strap to hold it in its position.
The patient use his other arm which is not paralyzed to push the syringe Fig (3) which injects a
hydraulic fluid inside the actuator Fig (1) with the help of inter connecting pipe Fig (7). The
maximum height that actuator Fig (1) can attain is 5.5 inches and minimum height it rests is 3
inches.
This will cause the actuator Fig (1) which has telescopic cylinders inside to raise above its normal
position (3 inches) and which in turn pushes the Fig (2). Since the Fig (2) is clamped at the end using
base clamp Fig (6), arm supporter Fig (2) will raise at an angle. The maximum angle through which it
can be raised is 45 degrees.
To increase the contact surface of actuator Fig (1) in its elevated position and Fig (2), Fig (8) is used.
Fig (8) improves the contact by making it a surface contact instead of a point contact.
The length of the arm supporter Fig (2) and wrist pad Fig (5) can be varied depending upon the arm
length of the patient. The minimum length that the can be incorporated is 9.5 inches and the
maximum length is 13 inches.
The minimum length is obtained by fixing the threaded rod projecting from the arm supporter to the
farthest hole of the wrist pad. The maximum length is obtained by fixing the threaded rod projecting
from the arm supporter to the nearest hole of the wrist pad Fig (5).
The arm supporter can be stopped at any elevation by cutting the supply of fluid to actuator Fig (1)
with the help of syringe Fig (3).
The device can also be placed at any arbitrary angle with respect to the table, so that the arm can be
elevated to suit specific applications.
3. DRAWINGS &DESCRIPTION:
Actuator Mechanism Calculation [Fig (1)]:
Fig 1.1 Fig 1.2 Fig 1.3
The hydraulic actuator is the most ‘critical component’ of the mechanism. Basically, it’s a single acting
telescopic actuator with 3 hydraulic cylinders stacked upon each other and move one inside the other. The
base can be clamped on the top of the table by nut and bolt arrangement. Initially, it rests as shown in Fig
(1.1). Once, the pressure is applied on the handle of Fig (4) the hydraulic pressure is transported to Fig (1)
through an incompressible fluid passing through Fig (7). This vertically pushes up the extending cylinders
inside Fig (1) which in turn pushes Fig (2) through Fig (8) as depicted in Fig (1.2). Fig (1.3) enlightens the
cross-sectional view of cylinder movement which is guided and sealed along the circumference. There are
rubber seals between the mating surfaces of 2 cylinders to prevent leakage of hydraulic fluid through edges.
The basis of sizing the actuator is as follows:
Diameter of Fig (4) = 1 inch.
Load applied by pushing force on the second arm = 50 N (reference from US center of health and safety).
Load applied on Fig (1) = 80 N (Std. human arm weight acting while sitting on a chair and performing
exercises).
Diameter of smallest cylinder in Fig (1) = 1.22 inch. (By Pascal’s law i.e, F1/A1 = F2/A2)
The successive diameters of the extending cylinders are evaluated based on minimum thickness of the
actuator to withstand the pressure, minimum clearance for casting the actuator, seal thickness. Same was
arrived to be 1.69 inch and 2.17 inch.
Since, the maximum pressure occurs at the top most cylinder in Fig (1). The major chance of failure is through
the ‘hoop stress’ generated due to the pressure. The cylinder wall thickness is obtained by computing
whether the provided thickness is sufficient for withstanding the hoop stress.
Diameter (d) = 1.22 inch
Hoop stress (σ) = Yield Stress (σy)/ Factor of safety
Factor of safety = 4 [General design criteria for project]
σy = 50 MPa ( Aluminum Grade 6061)
4. σ = (P * d) / (2 * t) = (0.1 MPa * 1.22) / (2 * t) = 12.5
t = 0.004 inch. Hence, we have provided uniform standard thickness of 2.5 mm (0.1 inch) for the actuator.
DESCRIPTION OF DRAWINGS:
1. Drawing A represents an exploded view of wireframe assembly model along with the different labels
each part represents.
2. Drawing B depicts the various degrees of motions the device can attain.
3. Drawing C represents the back side view to show the height of arm resting position from the top of
table.
4. Drawing D represents plan view of the device to show the minimum arm length at the lowermost
position of arm support. Also, the interconnections are made visible in hidden.
5. Drawing E represents right side view of the device to show the maximum arm length at the
lowermost position of arm support
6. Drawing F represents perspective views of the device of maximum and minimum arm lengths at is at
elevated position (450 from the horizontal).
7. Drawing G represents isometric view of solid model.
CLAIMS:
We claim:
1. A portable, table top arm supporter tailored to motivate stroke victims (in particular) or any users to
do their regular activities with the hand buckled to it through elastic straps. This also comprises a
wrist pad which is adjustable to suit different customers having different arm lengths.
2. The arm supporter of claim 1 is powered by:
Hydraulically powered single acting telescopic actuator which is self-locking and provides wide
range of positions by holding the arm supporter at various positions through a pin.
3. The actuator of claim 2 is triggered by:
A syringe and piston arrangement that injects pressurized fluid into the actuator through
flexible/rigid interconnecting tubing. The syringe and piston are custom made for this device.
4. The arm supporter of claim 1 is hinged by:
Base clamps on either side that is locked by nuts at ends to generate to and fro motion.
Drawing (A)
Figure
Part
represented
Fig 1 Actuator
Fig 2 Arm Supporter
Fig 3 Syringe
Fig 4 Piston
Fig 5 Wrist Pad
Fig 6 Base Clamp
Fig 7
Interconnecting
tube
Fig 8 ‘L’ Pin
Fig 9 Tube connector
