This is the second article on building my robotic first robotic arm project. I did create this project with the sole purpose of understanding the technological concept and theories behind building advanced robotic arms. In the second part of this article series, we are going to discuss about basic robotic concepts behind the process.
Building a robotic arm is a very cool idea. But understanding the fundamental theory behind is more complex.
Servos:
First we need to understand the what the servos are. In theory, the servo robotics or servos are the kind of robotic units that use an actuator called Servo motors to control their movements to a achieve a precise control over their movements.
Servo Motors:
A robotic arm has major functional points called ‘Joints’. To make these points functional, we are using a actuator known as ‘Servo motors’. so, they can be identified as the primary movers of a robotic system. Traditional Servo motors have brushes and they made a lot of noise during process. But with the emerge of brushless motors in recent years, they can be faster and can achieve more noise control. In these modules magnets are in the rotor, coil in the stator or around it, electronic circuits features the magnetic fields and the rotor motion is sensed by hall effect sensor.
Application of servo motors in Robotics:
- Intermittent operations
- Continues duty operations: When we drive a certain load in a particular speed or variable speed during a period of time, we need to take into consideration the load torque, speed and if electronic circuit is able to supply the required current and voltage.
Servo motor speed:
At first, we need to calculate speed of load, reduction ratio value by gearbox and the horse power or KW of the motor drive capacity.
Servo motor gearbox:
Every motor drive operates at a specific load, and typically, the motor runs at elevated speeds, such as 3000 rpm or higher. To manage this speed, we must select an appropriately sized gearbox since it affects the speed of the carried load. If the speed fluctuates rather than remaining constant over time, we need to determine a solution for this issue.
selecting a servo motor based on the task:
We must verify if the motor is capable of delivering a specific torque and speed as per the manufacturer’s user manual catalog, check if the electronic amplifier can handle the necessary current, and confirm that we have sufficient voltage to support the load. It’s essential to ensure that a motor does not overheat during its operational period. Predicting a motor’s performance in advance is straightforward because manufacturers supply various formulas and graphs that assist us in selecting an appropriate motor drive.
Controlling inertia:
There are two inertias to consider when it comes to controlling inertia.
- Motor inertia
- load inertia
In the previous equation;
- G = transmission ratio
- l = Load
Coordinative robotic systems:
Today, vast-majority of industrial robotic systems are being made with following feature configurations:
- polar configuaration
- Cylindrical configuration
- Cartesian coordinate configurable
- joint-arm configuration
Most of the modern robotic arms belong to the 4th configuration of coordinative robotic systems.
Joint-Arm Configuration
previous figure is a primary example for joint-arm robotic systems. The concept of joint-arm is actually coming from the movement structure of human arms. In a human arm, there are two motion part; upper arm and under arm. upper arm is connected to the body by a joint and upper arm is connected to under arm by another joint. Both arm parts can make angular motions around these joints. Just like that, the a simple robotic arm can perform angular movement around their joints. so, they consist of two straight components which can Correspond to the human forearm and upper arm, mounted on a vertical pedestal.
Precision movement parameters:
Precision of a robotic movements can be dependent on 3 features.
- Spatial resolution: This is the smallest increment of movement into which the robot can divide its work volume. Spatial resolution depends on two factors: the system’s control resolution and the robot’s mechanical inaccuracies.
- Accuracy: This refers to a robot’s ability to position its wrist end at a desired target point within the work volume. The accuracy of a robot can be denned in terms of spatial resolution because the ability to achieve a given target point depends on how closely the robot can define the control increments for each of its joint motions.
- Repeatability: This is concerned with the robot’s ability to position its wrist or an end effector attached to its wrist at a point in space is known as repeatability.
There are two distinct elements concerning the robot’s precision. Accuracy pertains to the robot’s ability to be set to reach a specific target location. The programmed location will likely vary from the intended target due to constraints in control resolution. Repeatability refers to the robot’s capability to return to the designated point when instructed to do so.
The previous figure shows a basic example of precision movement of robots based on Accuracy and repeatability.
Joint-Arm Robots:
A joint arm robot, often referred to as an anthropomorphic robot, operates in a manner similar to a human arm. It is made up of two linear segments that resemble the human forearm and upper arm. These two segments are attached to a rotating base, creating a work envelope with a spherical form. This type of robot is highly dexterous due to all joints being revolute joints. It features three rotating axes.
Previously mentioned concepts can be used to design a robotic arm from the scratch. In the next article, we are going to talk about a detailed description on kinematics; a complex theory in modern physics.