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3 different humanoid robot head designs to generate facial expressions

The robots are not created equal and humans have different perceptions over the humanoid robot heads. These intelligent human-like machines are expected to play an active role in our daily lives in the near future and we need to communicate with these. Since more than 60% of human communication is based on facial expressions and gestures, the same distinct emotions common to humans play a very important role in human-robot interaction.

The primary goal of this article is to show you what features of a humanoid head contribute most to the people’s perceptions of its humanness. To find an answer, I analyze 22 humanoid robots with different robotic heads. What I found is that the number of facial expressions differs between the types of robots and the facial expression influence the perception of humans over the human-like robots.

From the multitude of humanoid robots to choose from, I select three types:

  • humanoid robots with an interactive robot heads based on LEDs and speakers;
  • humanoid robots with kinematic heads;
  • humanoid robots with animatronic heads and flexible skin;

These three types of robotic heads should generate emotions and interact with humans in a more natural way. Let’s say that something better than a human and its pet.

While the most primitive robot head can generate basic emotions like happy, angry, surprised, sad, disgusted, fearful, the most advanced robot head can express at least 21 distinct emotions. Almost the same as a human head.

Humanoid robot head 21 emotions

Humanoid robot head 21 emotions

Interactive robot heads

Studies have shown that using LED’s and a speaker to show expressions can have effects on the human-robot communication. The heads of humanoid robots explored in this category come equipped with a full – color range RGB LEDs in the eyes and forehead, and believe it or not, these are nine of the most popular humanoid robots available today in the world.

Interactive robot heads

Interactive robot heads with LEDs and speakers

Despite its simplicity, the LEDs are capable of displaying a wide range of colors and are very cost-effective. In addition, the robot heads have embedded cameras, microphones and speakers in order to interpret the human speaking and body language.

A robot head equipped with LEDs, cameras, microphones and speakers has advantages and disadvantages in approaching the emotions.

Without mechanical parts, the robot head is lighter and provide enough space to add additional components. Also, the components used to build a functional head are cheap and can be easily embedded into the head.

A sophisticated alternative to the robot head with LEDs and speaker is in the mix for a while and uses artificial skin and dozens of actuators to display emotions. But not everyone is comfortable when has around a robot with skin and a realistic face.

In conclusion, a long time from now the robots will come in many shapes, but most important is that a good part of this big cake of social robots will be simple and incorporate only a part of human traits.

The simplicity of these robots without moving parts brings a number of disadvantages to the users. One big disadvantage is the interpretation of the facial expression. When you interact with a robot, you need to understand the pattern of colors and the intensity of the color displayed in the eyes. In other words, you need to read a whole book with instructions before the first conversation with an anthropomorphic robot that shows its emotions via LEDs and a speaker.

In this dimension of robots with social and emotional skills enters the DARwIn-OP, HOAP-3, Pepper, Nao, UXA-90, Roboy, Robi and ASIMO. All these intelligent machines have attached heads with RGB LEDs into the eyes, and in special cases into the forehead. These LEDs are programmable and display the color according to the robot status, or better said its feelings are transformed in different lights.

Kinematic heads

Our faces are in continuous transformation when we communicate with each other. We put every time the facial expressions as a mask to send our message and gesticulate with our hands to illustrate a point. Robots can do all these expressions, but in a primitive way.

The animatronic heads are engineered to provide a communication way closer to people’s communication mode. It’s something more natural than LEDs and with large possibilities.

With these robotic heads, we enter into the area of complexity. An area of animatronic heads able to provide rich information to humans using movable parts. When the robot turns its head and moves the eyes, jaw, eyelids, and eyebrows, something magical happens and lead to an increased engagement with the humans.

Compared with a simple head with LEDs and a speaker, the kinematic heads are built with a variety of moving parts. Some heads from this category are designed to move only the eyes while others are able to move the eyes and mouth.

In the first category of human-like robots enters the Romeo, iCub, and Simon. These three robots are equipped with pan-tilt mechanisms for the eyes and eyelids.

Romeo, iCub, and Simon

Romeo, iCub, and Simon. Three humanoid robot heads based on kinematic features

We jump forward to another area with robotic heads that looks like the rebellious Sonny humanoid robot from the movie I, Robot. In this category enters RoboThespian, MERTZ, KOBIAN-RII, InMoov, Robotics Squared, and Fritz.

All these robots featured heads with moving eyes, jaw, eyelids, eyebrows, and neck.

Kinematic heads

RoboThespian, MERTZ, KOBIAN-RII, InMoov, Robotics Squared, and Fritz. Six of the most advanced kinematic heads

These heads are capable of displaying a variety of expressions and generate synthetic speech. Synchronizing these two expressions of emotions, the robot can mimic the human movements and gives you the feeling of pity or sense of compassion.

Digging deep into specifications, we find a complex world of actuators and components that works together and move in perfect synchrony. For example, the KOBIAN-RII head is featured with 27 degrees of freedom to perform facial expressions. All the mechanisms are placed in the head, a head no more than a Japanese female.

Animatronic heads and flexible skin

A good-looking robot is hard to find, but as soon as they get realistic, they start to creep us out. Yes, these animatronics heads with its realistic skin that pushes the limits of human appearance.

After many years of researches, the roboticists realized that these realistic heads make people uncomfortable. More than that, these faces focus on emotions and mimic the human face and its movements.

Android heads

Android heads

The animatronic head is so real that can mimic all the 21 expressions of a human face. It’s the best and accurate system to match the robot facial expression to the words spoken.

One of its disadvantages is related to the manufacturing process that requires special tools and materials. These heads are so realistic that has teeth, ears, and animatronic eyes.

The Alice, Albert HUBO, Roman and Actroid are four of the most realistic robots with artificial skin and animatronics heads. For example, the Albert HUBO head is featured with 31 degrees of freedom only for head motions, which means that no more than 35 DC motors are embedded in the head to imitate various human-like motions.

The artificial skin is manufactured from a structured elastic polymer called Frubber. This material requires less force and energy to generate a variety of facial expressions.

Resources:
Development of an Interactive Humanoid Robot “Robovie”, Wakayama University
Happily Surprised! People Use More Facial Expressions Than Thought, Live Science
Museum Guide Robot with Effective Head Gestures, Saitama University

  • Posted in: Robots

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5 comments » Write a comment

  1. Hey there,

    The information on this page is very useful, good job!
    I have some questions about this topic. First of all, do you have any scientific paper / survey published in scientific conference or journal? This topic is very important for engineers / designers / roboticists.

    – do you know if there is a study behind the commercial robot head regarding design of the eyes and expressions (e.g. based on humans emotions and psychological studies such as FACS – Facial Action Coding System)?
    – In figure 1 you present 21 expressions/emotions, how did you categorize them, I mean, how did you get there? Is this categorization based on statements of the designers/creators of Albert Hubo / NAO robot?

    thank you,
    Cheers.

  2. Hi!
    I intend to make a robot head to serve in the cafe with the main task is to greet and take photos for clients. You think I should make a Animatronic robot or a Kinematic robot that better suited to my robot?
    Thanks!

  3. Interesting review. You should add lamp avatars (retroprojection of time-varying textures on a transparent 3D shape, e.g. Furhat). Note that the face of our iCub robot NINA is covered by a textile cover instead of the usual stretchable silicone layer. In order to display facial expressions, that counts is the number of underlying degrees of freedom (dofs) for the face, i.e. the actroid has no so many dofs as Kobian…

  4. That is very helpful, all of this. I’m trying to design a realistic video game that includes animatronics and this helps me with design of the heads, believe it or not. part of it was, if I tried to get inspiration online, I got Five Nights at Freddy’s, and the last thing I need is to get inspired by some overrated game. No offense, FNAF fans.

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