Electrical - Global Electronics

*TECHNOLOGY TUESDAY* 

Today we would like to use our Technology Tuesday to tell you more about some electrical components the Electrical Department designed and that were made in collaboration with our partner Global Electronics. Global Electronics is a company that is very socially involved, which is one of the reasons for them to become our partner. Another reason is their close collaboration with the Delft University of Technology in general. They are also a company that is supporting a new generation of engineers, for example by means of advice with regard to the manufacturability of electronical components used in high-tech projects. Furthermore, all their products are made in Holland, which characterizes Global Electronics. In the video below you see a nice overview of their complete production process.

Global Electronics is a valuable sponsor for Project MARCH, supporting the Electrical department in design and assembly of our main electrical components. The first of them is the PDB (shown in the first image), or Power Distribution Board, which manages power distribution in a smart way to ensure safe usage of the MARCH II. It can closely monitor information such as battery charge, power consumption and temperature. It also includes a booting system that we call Layered Booting, which makes sure that all control electronics are fully operational before enabling any motors to turn. This, along with an emergency stop, ensures that Ruben can safely operate the MARCH II.

The second device that Global Electronics has manufactured for Project MARCH is the GES (shown in the second image), or General EtherCAT Slave, which is a versatile system that can receive and process sensor data before sending it to the central computer of the exoskeleton. It processes data such as motor temperature, exoskeleton positioning (using an IMU) and pilot input. The GES is used in multiple locations of the MARCH II, including the legs and back of the exoskeleton.

We would like to thank Global Electronics in this way for all their support this year!

Frame

*TECHNOLOGY TUESDAY*

Today, we will talk about some parts that have been created by the frame department. They worked very hard in the past days and we can tell you that all the components are finished and that the ‘bones’ have already been assembled in the exoskeleton. We would like to tell you more about the fixtures today. 

The fixtures are the connections between the pilot and exoskeleton and hold the pilot in position in the exoskeleton. It is important that the fixtures fit perfectly to the skin and do not damage the skin. Somebody with a spinal cord injury cannot tell if the fixtures are too tight or squeeze somewhere. If the fixtures would do this and the pilot gets wounded, that wound would take a very long time to heal due to the decreased blood circulation of people that need to sit all day.

Some of the fixtures carry a lot of weight and others have the function to guide Ruben's legs while he is moving. The fixtures under the knee will carry the heaviest weight and must therefore be very strong and rigid. It is also important that you can open the fixture so that Ruben can go in and out the exoskeleton properly. The first image shows this aluminum fixture that we produced in-house. By pulling out the pen (indicated with red) and releasing the two screws, this fixture can flip open. The two screws are a safety measure to assure that the fixtures cannot open spontaneously during walking.

The fixtures that carry less weight are not made of aluminum but fabric. These are custom-made with the sewing machine. We also added padding so that these fittings are softer and fit the skin well. Thanks to these custom-made fixtures, we are well prepared to start the training program with Ruben.

Software & Control

*TECHNOLOGY TUESDAY*


Last time the Software & Control Department presented and explained their concept for the gait pattern generator during Technology Tuesday. In the meantime they finished this application and in the movie below you can see a demo of this application. In this way you are able to see how the application works and how they will use it to bring the exoskeleton to life!

Electrical

*TECHNOLOGY TUESDAY*
Today it’s time again for an update from the Electrical Department. This time they will tell you more about the wiring of the exoskeleton. These wires are very important for communicating all signals to the right components of the exoskeleton in the right way.

Did you know that the new exoskeleton of Project MARCH has over 200 cables measuring a total length of over 38 meters. It may sound like a lot, but it’s peanuts compared to the blood vessels and nerves that these cables resemble in our exoskeleton. A human has around 250.000 kilometers of “wiring”!

Cabling in the MARCH exoskeleton is a science in itself. A lot of parts need to be connected, but there is also a lot of parts moving around the joints. This makes the wiring in the exoskeleton tricky. On the one hand, you do not want the wires to break when you bend your leg and the cable becomes too short. On the other hand, a lot of slack in cables might get caught behind the obstacles that we want to overcome!

Special automated tooling helps us find the optimal length for each wire. Just long enough to bend, just short enough to stay out of harm’s way. The optimal cable tree is what we have built over the last couple of weeks. The picture that you find with this post shows most of the wiring of our cable tree.

Frame

*TECHNOLOGY TUESDAY*

Today it’s another Technology Tuesday of team frame! They also made a lot of progress and the complete frame is being produced as we speak. We expect to receive all milled parts, such as the hip structure and the bones, very soon. After this, the real work can finally start: the assembly of the whole exoskeleton!

During the assembly of the frame it is of course very important that all separate parts are connected to each other in a good way, so that the optimal stiffness and with that the safety of the exoskeleton is being guaranteed. Therefore, we make use of special connectors that fit each other perfectly and that are being connected by means of screws. In the first image one connector of the hip structure is shown, which will form the connection with the upper leg. The whole hip structure is shown in the second image. In order to connect these parts, the screw thread will go through the holes that are visible in the image, which will fit the holes of the connector of the upper leg perfectly. For these holes, we make use of inserts (helicoils). These are the small round components of the third image, on which also a part of a connector can be seen. The reason we do this is to make sure the screw thread of the screws we use to connect the connecting pieces will not break down in the aluminium, which is used for the frame. Screws of steal are namely harder and stiffer than the aluminium hole into which the screw goes. If you will put a lot of force to this bolt (this happens when Ruben is walking in the exoskeleton for example), the screw thread will slowly become defective. These helicoils make sure the steal of the bolt will pull on the steal of the helicoil instead of the aluminium. In this way, the screw thread will be loaded less and it is able to divide the forces better.

Besides, we make use of Nordlock locking rings for all connections. These makes sure the bolts cannot get loose by relaxation of the material or by just some vibration. These rings are designed in such a way that there is more force needed to unscrew them than when you screw them on.

In this way, we are able to produce a very strong and stiff frame, which is of course very important to let Ruben walk safely in the exoskeleton once it is finished!

Mechanical (ankle)

*TECHNOLOGY TUESDAY*

Today it’s the first Technology Tuesday of team ankle! After finishing the design of the knee and hip joints of the exoskeleton, it was time to start focusing on the last part of the exoskeleton: the ankles. In order to do so, a new department was established again, consisting of team members of the HMI department and the joint department. 

In a very short time they completed all steps of the design process and a design for the ankles was created. All these steps are shown in the first picture. First, they started with a brainstorm, from which several promising concepts followed. Some of them were elaborated in more detail. After that, prototyping was started, during which even a deck of cards has been used! By doing this prototyping they were able to get a good picture of the chosen model, which was elaborated in more detail and was programmed subsequently. This resulted in the CAD Design. The final design consists of a rigid ankle with an insole, which is produced especially for Ruben. They also chose a swappable connector, which is shown in the second picture. This connector forms the connection between the ankle and the lower leg. It is, as the name already suggests, swappable and this makes it possible to try out different positions. This connector was programmed first, after which it was produced by means of the CNC machine. The programmed production process can be seen in the movie. 

At this moment, the other parts of the ankle are also in production, such as the foot sole and we expect to receive them soon. This makes it possible for us to start with the first tests with our ankle and the ReWalk of Ruben in the near future already by connecting the ankle to the ReWalk.

Mechanical (joint)

*TECHNOLOGY TUESDAY*

Today it’s time for a new update with regard to team joint! In the meantime, the first iteration of our homemade joint came in and we started with the testing of this joint. But how do we operate during this testing phase? 

First of all, the dry assembly takes place. This means that all separate parts of the joint are being assembled, during which no grease is used yet in the bearing and the harmonic drive. This first dry assembly is important in order to precisely adjust the encoders (angle sensors), and with that the angle the joint will make. 

After this, it’s time for the first simple tests with regard to position control. This is required to verify the encoders are functioning properly. This first test is shown in the first movie, in which is can be seen very clearly that the joint turns to two different positions. 

Subsequently, it’s time for the wet assembly. For this the whole joint is first being stripped down again and a lot of grease is rubbed in, before the joint is assembled again. This can be seen in the second movie (the time-lapse). This grease improves the lifetime and the efficiency of the joint drastically. 

After that it’s time for the real deal: the testing of the moment of force the joint can deliver, and with that the force it can provide. For this we make use of dumbbells and the set-up shown in the first photo. In this way, we are able to attach different weights to this set-up and with that we can measure the exact moment of force the joint can deliver. Besides, we can use these dumbbells also to keep ourselves fit during waiting of course, as you can see in the last photo! 

Software & Control

*TECHNOLOGY TUESDAY*

Today it’s the Technology Tuesday of the Software & Control Department again. They made a lot of progress in the meantime and they would like to tell you more about this in this Technology Tuesday!

Last time we talked about the different commands we can send to the motor, this week we will show where these commands come from. 

They are generated in the gait generator. This is a kind of app, which we can use separately from the exoskeleton to design different gait patterns. He is able to save the generated joint angles, that can be uploaded to the exoskeleton subsequently, so that it can execute these angles. 

The gait generator starts with the graphic user interface (GUI), in which the user (the one that programs the gait pattern) can choose which parameters he would like to use to design the desired gait pattern. He or she can for example choose the angle the knee will make or the x-position of the foot. In this way, different separate points can be chosen, which the gait pattern has to follow; in this way you can say, for example, that when the step is completed for 80% the knee should make an angle of 60 degrees. These points are what we call the key-events. 

These key-events go into the spline generator after that. This spline generator will interpolate between all chosen separate point, so that a continue gait pattern is generated; these are the so-called splines. These splines will go to the kinematics block afterwards, together with some specific parameters of our pilot, such as the length of his upper leg and lower leg. In the kinematics block the other two required parameters are being calculated, with the help of the parameters that were chosen beforehand. In our case these two other parameters are the angle the hip should make and the y-position of the foot.

Now the gait pattern is finished and it is saved and judged by the gait checker. Beforehand specific wishes/requirements for the gait pattern are determined, such as the maximum velocity of the joints and the step length, and by means of the gait checker it is checked if the gait pattern meets all these requirements. So, the pattern receives a kind of mark. Subsequently, the generated gait pattern is sent back to the graphic user interface so that the user can see what kind of gait pattern he or she created. This finished the design loop.

All different steps are shown in the image.

S&C TT .png

Human Machine Interaction

*TECHNOLOGY TUESDAY*

Today it's the Technology Tuesday of the Human Interaction department. They are focussing on the interaction between the pilot and the exoskeleton, as the name already shows. Therefore they are responsible for the design of the input device, which makes it possible for Ruben to control the exoskeleton safely

The idea is that the pilot controls the exoskeleton via the handle of the crutch. To keep balance during walking in the exoskeleton, the pilot uses crutches. By placing the input device in the crutch, the pilot is always able to control the exoskeleton in a safe way. On the picture the design of this handle is shown including the input device. On the handle two buttons are place, by which the the exoskeleton can be put into a particular mode. Furthermore, you see a "big hole" in the model, which is meant for the screen. On this screen it can be seen very clearly from which actions the pilot can choose to execute, such as standing up, climbing a stairs or go down. This is important for the pilot to be sure which action he will let the exoskeleton perform. On the first movie you can see the two different buttons by which the pilot can control the exoskeleton. It is designed this way to guarantee extra safety. Furthermore, you can see on the movie all different actions the exoskeleton can execute. In the end, the Software & Control department is responsible for programming this actions, so that the pilot is actually able to execute them with the exoskeleton.

When the pilot executes a particular 'state' a signal will be sent to the master (the central computer of the exoskeleton), which will determine if the pilot is really able to execute the action. This can be seen in the second movie. This is done, since the master has all the information about the the joints, by which the master can determine very precisely if something is possible or not. In case something is wrong with the exoskeleton, you will see an error on the screen of the input device. This is also done because of safety reasons.

Electrical

*TECHNOLOGY TUESDAY*

Today it's time for the Electrical Department, that will tell you more about their home made Power Distribution Board!

One of the projects of the Electrical Department is the Power Distribution Board, or PDB. The PDB has the ability to connect to the battery of the exoskeleton (the big gold-colored on the right and bottom on the first picture) and distribute the power to both the four joint motors (holes at the top) and the electronics (white connector at the bottom), hence we call it the Power Distribution Board. It includes safety features such as an emergency switch, which can be controlled by an external button that connects to the board (black connector on the right). Moreover, the PDB is fitted with multiple sensors that monitor the power system, such as temperature, battery voltage and power usage of the motors. These are useful to check if the exoskeleton is properly functioning and also gives us valuable data during operation. For example, how much power are we using while climbing stairs? All monitoring and control is handled by the “MBed” (the blue rectangular device in the middle of the first picture) which can communicate with the “brain” of the exoskeleton through a communication device that is placed in the gap on the left of the PCB. Finally, there is the grey component in the middle-right, which converts the voltage meant for the motors to a suitable voltage for the electronics. This enables us to use one battery instead of one for the motor and one for the electronics.

A nice sideview can be seen in the second picture.

Mechanical (joint)

*TECHNOLOGY TUESDAY*

Today is for the joint department. They are responsible for the design of the joints of the exoskeleton. A compact joint design is one of the main focus points of this year.

The base of our joint design was a very compact gearbox (Harmonic Drive) to allow high transmission in a small volume. We also custom-picked all the other components: a small yet powerful (drone) motor, very strong angular bearings, oil seals to protect our parts from grease and precise encoders that can measure the angle of the joint for our Software & Control boys. On the first photo a schematic overview of the joint design is depicted with all these components.

To fit all these components in our joint we designed our own housings to complete the actuator. This comes with a lot of difficulties for our engineers, as all of the different part have their own requirements on size and tolerances. To accomplish this a lot of construction drawings are made, which are being optimized continuously. On the second picture some of the drawings can be seen.

At this moment the first joint is in production, so we expect to be assembling our first joint any time now, after which we will start testing our design.

Mechanical TT 1.png

Frame

*TECHNOLOGY TUESDAY*

Today is all about Team Frame. They are responsible for the design of the entire frame of the exoskeleton, consisting mainly of the bones and the fixtures. The fixtures are the points of interconnection between exoskeleton and the body and ensure that the pilot is fixed in a good and safe way while walking in the exoskeleton.

The past weeks they mainly worked with CATIA, a software program that is used to design mechanical objects. In this program they made the bones and they put the fixtures in the right positions, after which they will now start checking what impact these positions have on the entire exoskeleton. By doing this they want to find out if the fixtures are in the right place by loading them into the assembly. Together with the joint an iteration will follow on the shape of the bones and soon the wiring and all other further detailed engineering will take place. The bones will most likely be made of aluminium. Some designs that are made in CATIA are shown in the pictures below.

Software & Control

*TECHNOLOGY TUESDAY*

We have something new! From now on every Tuesday one of our technical departments will give a brief explanation about the parts of the exoskeleton they are working on and with that they will explain the technology behind it in more detail! Today we start with Software & Control.

The Software & Control Department of MARCH has worked with the test setup that is shown in the video below for the last few months. This setup contains the exact same electronics as the final joint of the MARCH II. In this way we can test our software already far before the production of the joint is ready!

To this setup commandos can be sent like "turn the motor to angle a" or "turn the motor with speed b". Later on the gait of the exoskeleton will be brought to life in this way. We can also let the motor sing by running it on frequencies that fit the notes of a particular song as can be seen in the following video!