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An introduction to actuators and their role in the field of robotics.
Two common features found in robotics projects include the ability to navigate and avoid obstacles, and to interact with or manipulate objects. To implement this functionality, robotics developers rely on actuators, which are components that turn electronic commands into real-world movements.
Of course, it should be no surprise that there are many different types of actuator hardware options for different applications. In this article we&#;ll review the different types of actuators commonly used in robotics, discuss some of the basic considerations for choosing them, and explore how to interface with them.
There are five general types of actuators used in robotics projects:
Robots can be built for a variety of purposes, functions, and operating environments, so there are a lot of aspects to consider when choosing actuators such as:
Purpose and intended functionality
The type of actuator required for a given application will depend on the robot&#;s purpose and intended functionality. For example, a DC motor will likely be used in conjunction with a drivetrain to allow for mobility, while a servo is often used to provide articulation such as that found in a robotic arm.
Physical requirements and constraints
Once the type of actuator has been decided upon, developers should look at the physical requirements and constraints. The first aspect to look for is the physical size and weight of the actuator itself to see if it will fit where it is needed, and if the combined weight of the actuator and mechanism on which it&#;s mounted is appropriate. For example, placing a heavy actuator on a small, weak robotic arm may cause the arm to fail under its own weight.
Mounting space and options
Similarly, developers must determine the mounting space available on or in the robot, and the mounting options provided by the actuator itself. Some actuators include separate mounting hardware allowing you to mount the unit in different orientations, while others come with integrated mounting points, requiring them to be installed into a specific position and orientation. Developers may also need to adapt the actuator to the mechanism that it&#;s controlling (e.g., control linkage). For example, a servo may include different types of servo horns that attach to the actuator&#;s output shaft, to provide different options for mounting control linkage.
Digital interfaces
Another aspect to look at are the digital interfaces available on both the actuator and the microcontroller responsible for controlling it. For example, servos generally have three wires including ground, power, and a control signal. Depending on the power requirements of the actuator, you may be able to power it directly from the microcontroller, while in other cases, power may need to be supplied from elsewhere (e.g., the microcontrollers are often limited to around 5VDC). The power consumption is often dictated by the amount of torque provided by the actuator and the amount of load it handles while in operation. So be sure to gather the specifications on the actuator&#;s power requirements, as this will affect how long the robot&#;s batteries will last.
Strength and Power
Depending on their intended usage, developers should ensure that a given actuator is strong enough to get the job done. For example, a DC motor must be selected such that it provides enough power to the drivetrain to move the robot and the robot&#;s load in the operating environment. If the environment is difficult to navigate (e.g., muddy terrain that causes slippage in the drive train), and/or the robot&#;s load becomes overly heavy, these worst-case scenarios need to be considered up front during actuator selection.
Communication protocol
Finally, the communication protocol must also be considered. Many actuators support communications using pulse width modulation (PMW) while some may support serial communications.
Hobby Versus Robot Grade Servos
There are two general grades of servos: hobby grade and robot grade. This distinction exists primarily because the radio control (RC) hobby industry has had decades to develop small, consumer/hobby-oriented servos (e.g., for RC cars), while the robotics industry is still relatively new.
Hobby-grade servos are relatively low cost and usually handle lower payloads than their robot-grade counterparts. They tend to have a limited rotational range and often only support communications via PWM.
Robot-grade servos offer a number of benefits over hobby-grade. Physically, they often provide more torque and include multiple mounting options. From an electronics standpoint, they can often be daisy chained and may be individually addressable through serial packet communications (e.g., via UART). In addition, they often provide two-way communication to send telemetry data back to the microcontroller such as temperature readings, and load monitoring, and provide the ability to vary torque.
Another nice option to look for on some units is a sophisticated microcontroller to which tasks and logic can be offloaded, freeing up your main control board for more general tasks. In some cases, the more sophisticated microcontrollers also support firmware upgrades.
Controlling it All
There are a number of platforms out there on which you can build your robots and control your actuators. One notable platform is the Qualcomm® Robotics RB3 Platform, and corresponding Qualcomm Robotics RB3 development kit, which is based on the Qualcomm® Snapdragon&#; Mobile Platform for developing intelligent and power-efficient robotics, such as that demonstrated in our seeing and hearing robotic arm project.
Figure 1: Qualcomm Robotics RB3 Development Kit
Developers can interface this kit with their actuators using the board&#;s expansion connectors. For example, the expansion connector&#;s GPIO pins can be used to send PWM signals to an actuator, while the UART pins can be used for serial communications with actuators that support serial packets. In addition, the board supports numerous other connection types (e.g., SPI, I2C, etc.) for interfacing with other systems.
As you can see, there are a number of important decisions to be made when choosing actuators for your robotics projects. Making the correct choices will create a robot that lives a long and useful life.
Author&#;s Bio
Rajan Mistry is a Sr. Applications Engineer at Qualcomm Technologies, Inc. with the Qualcomm Developer Network team. His role is to help grow the developer community and work on the next generation of solutions that utilize our technologies.
There are various types of robot joints. It&#;s helpful to learn about these different joints so you can better understand the workings of the robots you are using.
Each joint type will affect the range of motion and capabilities of your robot.
Goto ARCSEC DRIVE to know more.
The challenge for newer robot users is that there are different ways to categorize robot joints. This can make them confusing.
A basic understanding of the types of joints can really help you get the most from your robots. In this article, we explore the various ways you can look at robot joint types.
Like many people, you might just look at a robot and see it as a single machine. The robot operates as a single unit. However, you can also &#;zoom in&#; on the robot and look at its component parts.
All industrial robots are basically just a chain or collections of &#;joints.&#; Robot joints are mechanisms that create motion in one or more of the robot&#;s axes. Together, the robot&#;s joints create the desired motions of a robot&#;s limbs.
It&#;s helpful to know about robot joint types so you can understand which robots will be most suitable for your needs.
There are 3 basic ways you can categorize robot joints:
Each of these offers a useful perspective as to what makes a particular robot joint work. We&#;ll look at each of them in turn below.
The first way to categorize robot joints is by their actuation type. An actuator refers to any mechanical or electromechanical device that creates motion. The actuator generates a force using a particular type of energy.
Here are the 3 basic types of robot actuators:
An electric actuator converts electrical energy into motion with an electric motor. This creates a torque that moves the robot joint.
Electric actuators are probably the most common actuator type in robotics. They are fast, precise, and very portable. Although they are not as powerful as the other 2 types of actuator, they offer a good cost-to-strength ratio.
A pneumatic actuator creates force through the application of compressed air. As many manufacturing facilities already have pneumatic lines installed, this can be a handy option and is often used for robot tools.
Benefits of pneumatics include its fast speed and simplicity. However, it offers limited power compared to hydraulics and requires a lot more extra hardware (pumps and pipes) compared to electric systems.
A hydraulic actuator uses pressurized liquid to create motion. They offer more strength than the alternatives, which is why hydraulics are often used for heavy-duty applications.
Hydraulic robots are often the strongest with a high range of mobility. However, they are expensive, require high maintenance, and can be very messy if the liquid leaks.
Another way to look at robot joints is to classify them by how they move. This is determined by their kinematic design. Each joint will have one or more degrees of freedom which are arranged differently depending on the joint type.
Here are the 3 most common joint types by kinematic design:
A linear or prismatic joint can move in a translational or sliding movement along a single axis.
It is probably the simplest type of joint to imagine and is the easiest to control. Actuating the joint makes it longer or shorter.
A revolute or rotational joint moves around a point about one degree of freedom. You can think of a revolute joint as being like the elbow joint in your arm &#; it can bend only in one direction.
Most industrial robots comprise a series of revolute or rotational joints. As a result, there are well-established control strategies for revolute joints.
A spherical joint can move in multiple degrees of freedom around a single point. You can think of a spherical joint as being like the top shoulder joint of your arm &#; it can move in multiple directions but around the same point.
Spherical joint control can get quite complex. Sometimes, it&#;s easier to describe the spherical joint as being 3 revolute joints with an axis that intersects at a common point.
The last way to look at robot joints is often the most useful for industrial robotics. Here, we look at the robot joint by its function or role in an industrial manipulator.
The 3 functions of an industrial manipulator joint are:
The shoulder joint sits at the base of a robotic manipulator.
It is often the biggest joint and determines how much the robot can turn around. It has the most significant effect on the size of the robot&#;s workspace.
The elbow joint sits in the middle of the robotic manipulator.
It has the most impact on the robot&#;s lifting strength and sets a large proportion of the robot&#;s range of motion. If the elbow joint is restricted, the robot&#;s workspace will also be restricted.
The wrist joint sits at the end of the robotic manipulator.
It has the most effect on the position of the robot&#;s end effector. Often, wrist joints can spin a full 360 degrees. It is also subjected to more vibrations caused by the environment than other joints.
Now that you know the basics of robot joints, you can understand a little more about how robots are designed.
However, unless you are building your own robots, you probably don&#;t need to know much more. It&#;s most useful when you know the type of robot that you will use and how you can apply them to your particular application.
With the right robot programming tool, the software handles most of the complexity.
What questions do you still have about robot joints? Tell us in the comments below or join the discussion on LinkedIn, Twitter, Facebook, Instagram, or in the RoboDK Forum.. Also, check out our extensive video collection and subscribe to the RoboDK YouTube Channel
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