ANTHROPOMORPHIC ROBOT RECAP

Hello everyone, it’s been a while since we update our advance with the robotic arm, we did it this afternoon, but this is a resume of our story.

As you know, we been through a lot of problems and failures, fortunately, the practice make us smarter and we found a solution for each problem that we had. Also, we realized that the details matters.

Next, we present to you the final robot before and after all the modifications. That way, you can notice the big steps of desing and interface modelling improvement.

MECHANICS TRANSFORMATION

The mechanical components were the most modified part in our robot, as you saw along the previous posts, these parts had a huge changes. In the following pictures we show the previous and not so bad ideas that we had to make the structure of the robot.

Those pictures show our first ideas creating our robot, we were so exited about that… until we realized that the robot doesn´t reached the 20 x 20 x 20 cm cube. However we encouraged this problem and changed the structure for the final presentation, to illustrate this the next pictures show the results.

That transformation was awesome!

ELECTRICAL TRANSFORMATION

This is going to be short, the first servomotors that we had, were tiny and not so powerfull to lift the 200 g load. We decided to change them, for this reasons:

Because the servos were weak.
Because we need it.

The following pictures shows the before and after of the servomotor component:

Just imagine, the first servomotor were so weak that with only the weight of the arm fell, and with the second one we become capable to lift 200 g.

INTERFACE TRANSFORMATION

To control the robot, we create a graphical interface, and like the previous transformation this teach pendant also went along a notorious transformation.

The following picture shows what the interface looked like:

And the final interface become to the next one:

What a change… isn’t it?

Finally, we’d like to show some pictures of our robot in the final presentation.

We hope you enjoyed following us through all this construction, and find some motivation if you want to build a robot.

Success doesn´t just find you,you have to go out and get it.

Final Project: Implementation of an Anthropomorphic Robot

INTRODUCTION

This robotics project were developed for academic reasons, the anthropomophic arm is one of the basements for the history of robotics, and this type of robot is the one which is the most similar to the human body. The fingers,the arms, the feets, in general the hole human body can be represented with rotational joints. The complexity for the construction will depends in how is detailed and the precition for the movements that the robot will realize.

In the following sections, the development for the robot wil be explained in detail, with the sections, will be easy to understand how the robot works and how the robot were constructed along the semester.

STRUCTURE

1	Base for the robot arm
2	First link for the robot (shoulder)
3	Last 2 servomotors (rotational joints for links 4 and 5)
4	Second link for the robot (arm)
5	Third link for the robot (wrist)
6	End effector (in this case is a hook)
7	Roller ball transfer
8	First servomotor (first rotational joint in the base of the robot)
9	Heavy basement for the robot

3R DEMONSTRATIONS

Direct and Inverse Geometric Model

The first picture, shows how the Direct and Inverse geometric model works in the graphical interface, that example is for a [45°,45°,45°]’, example, as you can see in the DGM section, the answers given by the program, are the positions in x,y and z respectively. Those coordinates are used to make the prove with the inverse geometric model in the section which is called IGM, the results obtained in that section relates to the given configuration in radians for the [45°,45°,45°]’ angles. The cells that are on green correspond to the possible solutions that the robot could achieve. And the red ones are the solutions which does not achieve.

The second one, shows another example with a configuration on the DGM with [60°,70°,90°]’, and at least one configuration given by the IGM corresponds to the given configuration in the IGM in radians.

ACCURACY AND PRECITION

The values for the precision were measured in each joint for the angles given in the teach pendant and the real angles. All measures were expected to be in 45°.

JOINT 1	JOINT 2	JOINT 3
48°	40°	45°
47°	40°	48°
50°	43°	47°
46°	38°	46°
48°	40°	45°
47°	39°	48°
50°	40°	47°

For reasons of time we only take 7 measures for each joint and making the calculations we obtain the results shown in table

	JOINT 1	JOINT 2	JOINT 3
PRECISION	3±0°	5±0°	1.57±0.16°

REACHABLE CONFIGURATIONS

Next, we moved the robotic arm manually reaching all the apex in that cube, we fixed with tape, the cube to a notebook to make sure it does not move.

Implementation of an Anthropomorphic Robot

For this part, will talk about the points fixed for the previous mechanical design, this changes on the structure are product of the unreachable points on the workspace, also some of these changes due to the weight of the last two links.

Figure 1 Robot base with 3 caster wheels to support the structure

To give more stability and support to the base 3 caster wheels where as shown in figure.

As shown in figure 2 the links 2 and 3 are going to be only one piece instead of a prismatic form.

The robot is already ensembled with the servo motors, the orientation of them is being checked.

ELECTRICAL TOOLS

180 DEGREES SERVOMOTOR

This servo has metal gears for added strength and durability. The rotational space for this robot is approximately 180 degrees, this servo allows the programming work. One advantage is that it will fit in small places, so the esthetic part for the RRR robot, does not be affected so much. The specifications are the following:

Weight: 13.4 g
Dimension: 22.5x12x35.5 mm aprox
Stall torque: 1.8 kgf*cm (4.8 V) and 2.2 kgf*cm(6 V)
Operating speed: 0.1 s/60 degree (4.8 V), and 0.08 s/60 degree (6 V)
Operating voltage: 4.8 V – 6 V
Dead band width: 5 microseconds

The complete installation for the robot is shown in figure 9 which consists on the mechanical part and the electrical components together in one structure, as mentioned, the esthetical part is still in progress, depending on future works.

This electrical design is not the final progress, there is some parts that are currently fixing.

GRAPHICAL INTERFACE: END EFFECTORS VELOCITY

To know the values, the section for the q vector up left of the graphical interface, is used to solve the Jacobian matrix for the actual configuration. There are some points to fix, like the values which are zero, but there are not represented as zero as expected.

Solution for the same configuration, coded.

Final Cartesian robot test

In order to end with this blog, we would like to share with you the last test we made with our PPP Cartesian Robot.

The task given to the robot was to pick a wine cork and place it in a container, emulating an industrial process

The Robot is ready for action

You can see the video in this link : https://youtu.be/5k8OdtcD58Y

Joint Movement

We are controlling our motors using Arduino UNO since it is kind of easy to link Arduino and Matlab. This way using our interface, which was made using Matlab, the motors will be able to move from the interface through Arduino. We have videos showing the first rotational joint moving, as well as the prismatic joint going up and down. However, since we can’t upload videos here, we converted it into a gif.

As you can se from the previous gif, our rotational link is functional and it can hold the weight that the prismatic joint brings to the robot. Next we can see our prismatic joint going up and down.

Our stepper motor, even though it is functional and can manage to move the last servo holding the robot’s end effector’s link; moves a little bit slow. Please keep in mind that the threaded rod by every revolution it makes, it moves the servomotor’s base just 8 mm.

Cartesian Robot Tests

Once the robot structure is completed, we move on to the straight line movements that can be made within the workspace.

The trajectory of the robot is given by the graphical interface, where it is possible to store the desired positions. As part of the first tests, the trajectories were given one by one to achieve the drawing of a triangle on a sheet of paper.

You can see the video in the next Link: https://youtu.be/9lyMGFMVsP4

6 DOF Robot simulation

HMI Video

In this post, we would like to share the last version of our Human-Machine-Interface, and the simulation of some straight line trajectories inside the robot’s workspace.

So far we are able to store 5 positions inside a workspace, represented as a cube with dimensions of 20x20x20 units.

We have simulated trajectories for our 6DOF version, we remark how the prismatic joints change its movements in order to reach certain position, we are looking now the action of the rotating joints added.

Update on Motors

Back when we started proposing our motors, we determined we needed 2 servomotors for our rotational joints. For the prismatic joint we would use a stepper motor. In the following pictures we show our final chosen motors.

Our stepper motor is a Nema 17 with a worm drive which holds a threaded rod that helps the prismatic joint go up and down. We have a base which moves together with our threaded rod and has the last servomotor on a planar base.

The first servomotor is at the base of all our robot. It was important to make sure that the motor itself doesn’t lift all the weight; so it has a special structure (aka the “Box”) with a “lazy susan” on top to hold all the mechanism we used for the prismatic section of the robot. While the last servo has our final link directly connected to it; and this will be the link in charge of holding the weight load.

We had to make some redesigns in our mechanical design but the concept is still the same. Here is our robot built with all 3 motors in place:

RPP – Mechanical Desing & DGM analisys

In this update we registred our mechanical desing for RPP robot.

The first step was create the desing of the structure in SolidWorks to make the mechanical pieces.

We had some troubles in the first desing, one of those was about the dimensions in MDF pieces, the box that unites the two prismatic joints was wrong, that’s why we had to remake the dising . This work is shown in figure 1.