0LAUK0 2018Q1 Group 2 - Prototype: Difference between revisions

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(changed 'ideal monitor guidelines' link to redirect to appropriate section of our SotA literature study)
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=== Degrees of Freedom ===
=== Degrees of Freedom ===
First of all the Degrees of Freedom (DOF) need to be considered. In total there are six DOF that can be included (3 linear x,y,z; 3 rotational), but each DOF makes the manufacturability of the prototype more difficult. Also, not every DOF is important to achieve the end result, which is a monitor arm that reduces neck and back complaints.
First of all the Degrees of Freedom (DOF) need to be considered. In total there are six DOF that can be included (3 linear x,y,z; 3 rotational), but each DOF makes the manufacturability of the prototype more difficult. Also, not every DOF is important to achieve the end result, which is a monitor arm that reduces neck and back complaints.
Looking at the [[Ideal monitor guidelines]], it was decided that the prototype will receive 3 DOF. The first one is a linear movement in the z-direction, to adjust to the body length of a person. The second one is a rotational movement in the xy-plane, to adjust to the angle at which the user is behind his or her desk. The final DOF is a linear radial movement perpendicular to the rotation in the xy-plane. This adjusts the distance at which the monitor is from the user. We have thought of adding a rotational movement in the yz-plane, but this did not seem necessary whereas the linear z-direction already sufficiently comprehends the height adjustment. The DOF are visualized in Mark I prototype.
Looking at the [http://cstwiki.wtb.tue.nl/index.php?title=0LAUK0_2018Q1_Group_2_-_SotA_Literature_Study#RSI_prevention:_how_to_properly_setup_a_computer_monitor Ideal monitor guidelines], it was decided that the prototype will receive 3 DOF. The first one is a linear movement in the z-direction, to adjust to the body length of a person. The second one is a rotational movement in the xy-plane, to adjust to the angle at which the user is behind his or her desk. The final DOF is a linear radial movement perpendicular to the rotation in the xy-plane. This adjusts the distance at which the monitor is from the user. We have thought of adding a rotational movement in the yz-plane, but this did not seem necessary whereas the linear z-direction already sufficiently comprehends the height adjustment. The DOF are visualized in Mark I prototype.


=== Dynamic Domain ===
=== Dynamic Domain ===
As with the DOF, the dynamic domain of the prototype is depending on the [[Ideal monitor guidelines]]. Taking these guidelines in account, the ideal operational domain (seen from the top view) of the prototype is a semicylinder with a radial distance of approximately 40 cm. This can easily be accomplished by using a 2-link arm with 3 rotational joints that can fully move in the linear y-direction. To move in the linear y-direction we have decided to assume that this can be actuated by the  systems that is already implemented in the Gispen TM duo desk.
As with the DOF, the dynamic domain of the prototype is depending on the [http://cstwiki.wtb.tue.nl/index.php?title=0LAUK0_2018Q1_Group_2_-_SotA_Literature_Study#RSI_prevention:_how_to_properly_setup_a_computer_monitor Ideal monitor guidelines]. Taking these guidelines in account, the ideal operational domain (seen from the top view) of the prototype is a semicylinder with a radial distance of approximately 40 cm. This can easily be accomplished by using a 2-link arm with 3 rotational joints that can fully move in the linear y-direction. To move in the linear y-direction we have decided to assume that this can be actuated by the  systems that is already implemented in the Gispen TM duo desk.


=== Forces ===
=== Forces ===

Revision as of 13:53, 29 October 2018

Introduction

This page explains the design-process behind the prototype made during this project. Suggestions for the final design are also given.

Important components that need to be kept in mind when making the prototype are:

  • Degrees of Freedom
  • Dynamic domain
  • Forces
  • Manufacturability
  • Compatibility
  • Simplicity
  • Movement
    • Kinematics
    • Arduino
    • Sensors
Mark I prototype

Degrees of Freedom

First of all the Degrees of Freedom (DOF) need to be considered. In total there are six DOF that can be included (3 linear x,y,z; 3 rotational), but each DOF makes the manufacturability of the prototype more difficult. Also, not every DOF is important to achieve the end result, which is a monitor arm that reduces neck and back complaints. Looking at the Ideal monitor guidelines, it was decided that the prototype will receive 3 DOF. The first one is a linear movement in the z-direction, to adjust to the body length of a person. The second one is a rotational movement in the xy-plane, to adjust to the angle at which the user is behind his or her desk. The final DOF is a linear radial movement perpendicular to the rotation in the xy-plane. This adjusts the distance at which the monitor is from the user. We have thought of adding a rotational movement in the yz-plane, but this did not seem necessary whereas the linear z-direction already sufficiently comprehends the height adjustment. The DOF are visualized in Mark I prototype.

Dynamic Domain

As with the DOF, the dynamic domain of the prototype is depending on the Ideal monitor guidelines. Taking these guidelines in account, the ideal operational domain (seen from the top view) of the prototype is a semicylinder with a radial distance of approximately 40 cm. This can easily be accomplished by using a 2-link arm with 3 rotational joints that can fully move in the linear y-direction. To move in the linear y-direction we have decided to assume that this can be actuated by the systems that is already implemented in the Gispen TM duo desk.

Forces

To function properly, the prototype should be able to lift the monitor easily from each position without damaging the actuation system. Forces can differ a lot due to change of arm length, and thus higher moments. To make sure this happens, the correct actuation type should be chosen. After also considering hydraulic actuation and servo motors, we have decided to use stepper motors for the prototype. Stepper motors are easy to use and can deliver high torque without gearing. A stepper motor also has a holding torque, which means that the torque will be kept even when no input is given to the motor.

Even though stepper motors are conventional, it is still possible that the full system needs more power to operate. An integrated spring system could be used to subtract the major part of forces needed to move the arm. These spring systems are already implemented in normal monitor arms. It was not possible for us to acquire such an monitor arm, so we decided to build our own. Because of manufacturability we have decided to not make an integrated spring system, but to assume this is implemented in the final design. Because of this, the prototype will be lightweight and carry a dummy monitor instead of a real one.

Mark V prototype

Manufacturability

We have decided to make the prototype using additive manufacturing because this option was available and this would later on result in easy assembly of all components. First all components were designed using the Computer Aided Design (CAD) software Siemens NX.10. During this process different electronic components were already chosen in order to design the monitor arm around it. The parts were printed from black PLA using an Ultimaker 3 in the TU/e innovation space. For the final design it is advised to use machined aluminium to increase the stiffness of the parts and decrease the tolerance.

Compatibility & Simplicity

The compatibility of the monitor arm and it's components is very important. As stated earlier, the monitor arm will be implemented in the Gispen desks and will also be operated from one control center and should cooperate with different types of software. This cooperation is assumed to work for the final design. For the prototype the monitor arm will run on a small computer with it's own software. The prototype is also kept as simple as possible, in orde to reduce the chance of failure, tolerances and the time limit in which a working prototype had to be made.

Movement

When the total design is finished and the prototype is ready to be assembled, the movement can be thought out. The movement is based on three main subjects: the kinematics, electronics and sensors. All subjects are made in parallel and should be combined when they are working separately.

Kinematics

The kinematics describe the coordinatesystem in which the robot arm is able to move. The kinematics are calculated using MATLAB R2017a. This is done with forward and inverse kinematics. The forward kinematics calculates all possible coordinates based on the domain and stepsize in which the stepper motors can move. When an input coordinate is given, the script finds the angles which are closest to this coordinates. The downside of this is that an exact stepsize is needed and that literally all possible combinations are calculated before even using an input. This resulted in matrices with over 8 million arrays, which is not optimal for a small computer.

The inversed kinematics are made the other way around, as it's name implies. The script uses x and y coordinates as input which it converses with trigonometry. A problem with this script is that some the used functions have asymptotes. This results in bad calculations close to certain inputs. To solve this the script is written for different coordinate domains.

File:Kinematics.jpg
Inversed kinematics of 2-link monitor arm

Electronics

Sensors