Building a 4-DoF Serial Robotic Arm with Smart Motion Devices

Introduction

Makers/hobbyists and academicians are often willing to build their own serial robotics arm. This is because the robotic arms have a good amount of engineering challenges and learning topics for their internals and how they work. Read our other blog post if you need some information about the different type of robotic manipulators and their building blocks.

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In this article, we will delve a bit more into the serial robotics manipulators and share a simple design on building an affordable and a decent performance robot. Let’s start with the ingredients first:

List of Items Required for Building a Serial Robotic Arm

There are 6 major components that are needed to build a Serial Robot Arm. Here's a the list of these components with some explanation as well:

1. Actuators: The serial robotic arm employs multiple motors for rotating its each or at least major motion related joints. Electrical motors (mostly DC, servo for high-speed or stepper motor for low-cost options), which are coupled with gear mechanisms are used to form the actuators of the robotic arms. There are minority cases where another type of actuation mechanism is used such as pneumatic or elastic materials, but those really are not something one can see in daily life.
2. Sensors: Encoders, loadcells, accelerometers and some digital Input/Output nodes are integrated into the system, offering different ways of feedback for control algorithms. 
3. Linkage and Mounting Parts: To interconnect the actuators to each other and also to make the robotic arm to reach to a distance, some linkage and also mounting parts are needed. The linkage parts can be considered as the exo-skeleton of the robotic arm, whereas the mounting parts may  not be seen easily. 
4. Control Unit/Box: An electronics control unit, mostly placed inside a bow or underneat the robotic arm. These are equipped with a specialized control unit that interfaces with Motors / Motor Drivers, sensors and other input/output devices of the robot.
5. Power Unit/Supply: A suitable and powerful enough power supply is required to power all the actuators, sensors and control unit/box.
6. Software: Robot Arms have 2 different software options. The industrial arms have a locked firmware and gives access to the robot through an API for supervisory control and robotic tasks. The open-source robots such as Acrobot provide direct access to the motor drivers hence gives the user the ability to control each joint individually. The latter option should also include kinematic and trajectory software functions for the robot to operate in a supervisory control manner similar to the industrial robotic arms.

Introduction to 4-DoF Robotic Arms

While 6 or more-DoF arms offer a wide range of motion and versatility, they often come with complexities that are not required for many common tasks. This is where 4-DoF robotic arms come into play, offering a more streamlined, efficient, and cost-effective solution for specific applications. 

Axes and Motion Capabilities

A 4-degree of freedom robotic arm -as its name stands for- has four primary axes that provides manipulator action and capabilities. These axes are as follows:

• Axis for Base Rotation: The base rotation axis allows the arm to swivel 360 degrees in a horizontal plane. This is particularly useful in tasks that require the arm to sort items from multiple directions or assemble parts that come from various angles.
• Axis for Shoulder Movement: The shoulder axis enables the arm to extend or retract linearly. This is crucial for tasks that require the arm to reach into confined spaces, such as retrieving items from shelves or extending over a conveyor belt to pick up objects.
• Axis for Elbow Movement: The elbow axis provides the arm with vertical movement capabilities. This is essential for lifting or lowering objects with precision, making it invaluable in applications like welding, where the arm needs to maintain a specific height for optimal results.
• Axis for Wrist Rotation: The wrist rotation axis allows the arm's end effector to rotate, adding a layer of finesse to tasks that require intricate movements, such as painting intricate designs or performing surgical procedures.

Use Cases and Applications

• Manufacturing: In automotive assembly lines, 4-DoF arms are indispensable for intricate welding tasks. Their precision ensures high-quality joins, eliminating the need for human intervention and thereby reducing the margin for error.
• Healthcare: In the medical field, these arms are revolutionizing minimally invasive surgeries. Their ability to maneuver surgical instruments with pinpoint accuracy significantly reduces the risk of complications, making surgeries safer and more efficient.
• Agriculture: In the realm of modern farming, 4-DoF arms are being employed to harvest delicate crops like tomatoes or strawberries. Their precise movements ensure that the fruit is picked without any damage, optimizing yield and reducing waste.
• Research and Education: Educational institutions and research labs are increasingly adopting these arms to study robotics kinematics and provide hands-on STEM learning experiences.

Advantages Over Other Types

• Cost-Effectiveness: One of the most compelling advantages of 4-DoF arms is their affordability compared to 6-DoF arms, making them a more accessible option for startups and SMEs.
• Ease of Use: The reduced complexity in the control algorithms for 4-DoF arms translates to a shorter learning curve, allowing operators to become proficient more quickly.
• Energy Efficiency: These arms are designed with energy conservation in mind. Fewer motors and joints mean less power consumption, which in turn leads to lower operational costs.

Control of the 4-DoF Robotic Arm with Smart Motion Devices (SMDs)

The Brain Behind the Brawn

Smart Motion Devices (SMDs) play a crucial role in the operation of 4-DoF robotic arms. They offer real-time monitoring and adaptability, adjusting motors control signals in real-time synchronously. Please check our Synchronizing Linear Motors and DC Motors article to learn how multiple SMDs can be interconnected and used for driving multiple and different types of motors synchronously.

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The synchronous motor control is especially valuable in robot arm applications, to achieve trajectory movement patterns, like placing an object in a confined or tight space. Each motor has to be controlled precisely during the course of motion (where the synchronous control comes into play) for the arm to follow a predefined trajectory.

In addition to the synchronous position control, the current level of the motors should also be monitored to see if the robot arm is moving freely or if it has hit any obstacle during its motion. Current limiting and active current monitoring are tremendously important for collaborative robot arm applications. Current monitoring is a built-in feature of the SMDs as well.

Last but not least, the sensor data needs to be read by the controller in a timely and precision manner as well. Robot arm can not see its environment directly hence auxiliary sensors are needed for this task. The sensor add-ons of the SMD family is a very neat feature that not only solves this requirement but also provides an easy and clean cabling all around the robot. Both the motor driver boards and also the sensor nodes are daisy chained, hence a single communication line passes both the motor and the sensor data to the controller. Please check the below diagram to see an outline for the connections:

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Bill of Materials

    Creating a 4-DoF robotic arm is not just about assembling mechanical parts; it's about integrating a variety of components into a cohesive, functional system. 

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Here's a list of materials you'll need, along with their respective roles in the assembly:

Mechanical Components

• Frame: Provides the structural integrity for the arm.
• Gearbox: Facilitates the mechanical advantage needed for lifting heavy objects.
• Bearings: Ensures smooth rotational movements at various joints.

Electrical Components

• Motors: Powers the arm's movements.
• Sensors (Encoders, Gyroscopes, etc.): Provides feedback for precise control.
• Power Supply Unit: Fuels the electrical components.

Control Systems

• Smart Motion Devices (SMDs): The control center for the robotic arm, offering real-time monitoring and adaptive control algorithms.
• Microcontroller: Executes the control algorithms and interfaces with the SMDs.

Software and Firmware

• Control Algorithms: Software logic that dictates the arm's movements.
• User Interface: Software for human-machine interaction.

Optional Add-ons

• Camera Module: For computer vision tasks.
• Grippers or End Effectors: Specialized tools for specific tasks, such as welding or painting.

The introduction of 4-DoF robotic arms represents a significant advancement in fields ranging from manufacturing and healthcare to research and education. The integration of Smart Motion Devices (SMDs) further enhances these systems with features such as real-time sensing, a built-in PID controller, and an easy-to-use graphical user interface. If you are a researcher, educator or industry professional, it is time to embrace this technology.