Is it technologically possible to build such a device?
Today the known technology is good enough to let us building such a walker. First I will explain the parts that I will use to build such a device. Then I will talk some about the calculations. Finally the topic will be the benefits of this device to a costumer.
As it is mentioned earlier the device would have tree main functions. They are Walking – Shaping – Sensoring. You can find the components that I will use for each function below. The components are under the title that they are most critically needed for.
If we look at the medical necessities of to make such a walker we see that we must use 12 actuators to reach our goal; acting like a human. Those actuators will be used 6 on each leg. Two on ankle (to lift the foot and to move the foot lateral), one on knee (to bend the knee) and tree on hip (to move the leg back – forth, to move the leg side to side and to turn the leg for changing walking direction).
Contrary to human the lover actuators must be stronger. Because every actuators are responsible for not only the lover attached parts but also the higher attached ones. That means the actuator on the ankle must also lift the whole body and for that it should be the strongest one.
The calculations shows us for a 40 cm step of a 1.80 meter 80 kg men the foot lifting actuator must have a torque of 560 Nm. Although the common actuators are very heavy at that torque the actuator that we will use there will be 8 kg and have the torque of 800 Nm. That motor is a special edition of Harmonic Drive AG Servo Actuator FHA-C / 32-C 320-H
This is the heaviest actuator and the most of the other actuators are much lighter. The sum of all actuators is a little less than 40 kg.
For more and detailed information please visit www.harmonicdrive.net.
The material we will use for the device should be light and strong enough
for efficiency. Although titanium like materials are strong, light and
perfect to use in rims of eye glasses to use it in a robotic device will be
too pricey. On the other hand to use a Magnesium Alloy would be much
reasonable. Compared to most other metals magnesium alloys are known with
their lightness, strong ness, resistance to high heat, easy manufacturing
capabilities and resistance to corrode. Today it is used in many different
product like automobiles laptops, nuclear centrals and robot
prototypes.
Shapingde material zorlanıyor
For more and detailed information please visit
http://www.azom.com/details.asp?ArticleID=355
A paralyzed human can not only move his legs, but also can not feel them. That also means he can not feel any danger either. The walker should be user-friendly enough to understand the actions that he wants to make immediately and should protect the patient while doing those.
We divided the sensors to three different categories according to usage area.
Force sensors: There will be several force sensor attached to body of the device. The ones beneath the foot are for calculating the ZMP while walking or standing. The ones that are at the back of the walker are for calculating the pressure while the patient is sitting or lying on bed.
Cameras and ultrasonic sensors: There will be some cameras and ultrasonic sensors which will sense the room that the patient is in. Those sensors are not only to prevent crumbling and falling by stopping the walker, but also to sense the distance of stairs, table or the object that the patient is directed and can calculate the measurement of the ideal step. This way a patient goes to near of a table very easily.
Temperature sensors: There will be two heat sensors on outside of each leg, so the system will protect the patient from going near a radiator, a burning oven or any kind of heater.
For more and detailed information please visit http://www.baumerelectric.com/en/shop
Our device needs approximately 10kW and 7 kg Li-Ion battery will be enough. But there are new generation battery prototypes which have promising energy efficiency and weight-power ratio better than current batteries.
For more information:
http://www.batteryuniversity.com/parttwo.htm
CALCULATIONS
There will be four datasheets. Those are the data’s that we use to make the calculations.
1) The Patient
| Height | 170 cm |
| Weight | 70 kg |
| The Approximate Height of Centre of Mass | 100 cm |
2) The Walker
| The Hip Actuators for Back and Forth | 2 x 1 = 02kg |
| The Hip Actuators for Turning | 2 x 1 = 02kg |
| The Hip Actuators for Lateral Movement | 2 x 1 = 02kg |
| The Knee Actuators | 2 x 6 = 12kg |
| The Ankle Actuators for Lateral Movement | 2 x 1 = 02kg |
| The Ankle Actuators for Back and Forth | 2 x 8 = 16kg |
| Total Mass of 12 Actuators | 36kg |
| Servo Drivers | 12 x 250gr = 3kg |
| Approximate Weight of All Sensors | 1kg |
| Battery | 8kg |
| Pumps | 2 x 2 = 4kg |
| Cards and Electronic Components | 1kg |
| Approximate Weight of Metal Body Components | 10kg |
| Counter Weight | 20kg |
| Total Mass of Walker with Actuators and the Counter Weight | 83kg |
| The Approximate Height of Centre of Mass Without the Counter Weight | 40 cm |
3) The Body Without the Counter Weight
| Height | 170 cm |
| Weight | 133 kg |
| The Approximate Height of Centre of Mass | 70 cm |
4) The Total Body
| Height | 170 cm |
| Weight | 153 kg |
| The Approximate Height of Centre of Mass | 60 cm |
| The Maximum Step Distance | 40 cm |
| The Maximum Stair Height | 20 cm |
| The Lateral Change of COM Respect to Counter Weight | 6,5 cm |
Benefits
The calculations below are not the exact calculations; they are written only for to explain the general working principle of the system.
Imagine there is a man named Tom who is paralyzed for over 10 years. He can use his arms and upper body but he can neither move nor feel his legs. Because it has been over 10 years his joints at his lover body are calcified. He is 170cm and 70kg.
Tom is our potential costumer. After we start to sell our walker he will
buy the product and let’s analyze the moves that he can make and its
benefits to Tom.
After Tom wearied the product he can make lots of moves. Let’s start with
lifting one foot.
Imagine Tom is standing on two feet. He decided to lift right foot and ordered the walker to lift it. In the beginning the COM is laterally in the middle of the body and at 60 cm high. The distance between the right foot and the left is 0,5 cm. After he ordered to lift one foot the pumps starts immediately to transferring the fluid. In less then two second the transfer of the counter weight fluid is over. Now the COM is 3cm inside of Tom’s left foot. In those two seconds the hip, knee and the ankle actuators also start to work and at the end of this two seconds not the whole bottom of the left foot but just the front of it is touching the ground. The acceleration of the left foot is over and from that point he will continue to lift it with constant velocity so the momentum does not affect the system. At the end of third second the lifting process is over. After that the system automatically uses the lateral ankle actuator to move the body and place the COM at the middle of the right foot.
Although to lift one foot has no important benefits by itself after understanding this it, it is easier to explain the plain straight walking. Tom has lifted his right foot and put it to the ground, 15 cm forth. Than he lift the left foot and place it 30 cm forth of the other foot. Because those steps are less problematic for both balancing and moving, now we will analyze Tom’s third step.
Imagine Tom decide to walk further. His left leg is in forth and the right one is at the back. The counter weight fluid is in the right foot. Each foot is 25 cm long. The actuators are not in the centre of the foot; from the attachment point it is 15 cm to front and 10 cm to back.
In the beginning of this step the COM is laterally 3cm inside of the right foot and frontally 2.5 cm inside of it. To make it more clear; without the fluid and with straight knees, COM should be right in the middle point which is 15 cm away from each knee. That point is just the end of right foot and 5 cm away from the left. Because to respect the fluid it is 2,5 cm inside of right one.
When he orders to walk the pumps will start automatically to transfer the fluid. That affect the COM and it slides 5 cm front. The COM is 2.5 cm away from the back of the left foot. The transfer takes less than two seconds. In that time the right ankle actuator and the left knee actuator also starts to work. By the time they stop the left knee is bended and the COM slides inside of the left foot. After that the actuators worked together and place the right foot 60 cm further.
That is how Tom will make one step of 30 cm in less than 4 seconds. With straight walking he can go anywhere he wants. With similar calculations Tom can walk, turn walk backwards and climb stairs. It is too complex to explain the actions like sitting or getting up because for those actions the upper body is passively needed.
The most exiting situation to analyze here is falling. Imagine Tom starts to fall. For a dynamically balanced robot it is the end of the world.
In our system the COM can laterally slide 6.5 cm from one foot to another. The affect of the counterweight is the multiplication of the weight of the counterweight and its COM s distance to the fares floor touching body. As an example Tom lift his right foot and he starts to fall to right. First of all this fall is much slower compare to any other robots fall, it takes more than a second just to louse its verticality for 10 degrees. By that time the two force sensors at the left of the left foot started to sense zero. The only thing that system has to do to stop falling is to place the right foot to the near of the sensor which senses the highest force. After that the distance of the floor touching body is so far that the result of the multiplication is high and the fall automatically gets prevented.
But now think how he will live with a walker. With using this product Tom can walk anywhere inside of his home. With the measurement of sensors and calculations he can go near by an object as example a table to do some work. He can use the bathroom alone. He can go to the bed alone. Shortly Tom can live at home alone
The outside of the home is a little harder than that. First of all although it is a danger to use this product other places than the plane floored ones, there are lots of places with straight floor like buildings, plazas or shopping malls. The shaping function makes Tom to get inside of his vehicle. The only thing that Tom should do is to prevent danger is to go to his garage with an elevator and to walk to his car on specially planed floor.
It is very obvious that there are many benefits of acquiring such a
device for Tom. With our walker Tom and millions of disable people like Tom
will be very pleasant if they can walk and live alone with our device again.
The only problem for those people is that: will the walker cause any medical
problems for them. In the next chapter we will convince you that there is a
great possibility that it will not.