THK's Robot Hand: A Behind-the-Scenes Look at Humanoid Robot Development

Development of Humanoid Robots

Even from a young age, many people have been fascinated by robots and wanted to operate one. Maybe some have even had grand dreams of designing a humanoid robot.

If you break the human form down into its components, it consists of the following features:

Imitating Function, Not Form

The childhood dream of developing humanoid robots will remain only a dream if you take a regular approach. You'll suffer setbacks if you attempt to exactly replicate the human form with machinery. However, there are two approaches to mechanization. One method replaces the human form as it is, and the other method achieves the abstracted functions without regard for form.

As an example, let’s take a look at the development of the robot hand. Over time, humanity evolved hands to perform various actions such as gripping and carrying, and they feature the following:

Do Humanoid Robots Need Five Fingers?

The humanoid robot is modeled after humans. If the end goal is to make a robot look like a human, then it will need five fingers. But if the goal is for the robot to take the place of a human, does it need that same number? If the robot is taking over a task, does it need to have the same kind of hand as a person? Human hands have over 20 degrees of freedom, so it would be extremely difficult just to build in enough actuators to control that movement at the same size of a hand. There are even more joints, so in addition to all of those mechanisms, you also need more motors, actuators, sensors, and wiring.

Aiming for the Smallest Structure Possible

One Motor

In trying to achieve the smallest structure possible, the challenge lies in how much you're able to simplify the human hand's functions of gripping, grasping, and pinching. To that end, it’s preferable to have one motor. Any more than that, and the size will go up. You'll also need more power and may run into problems with heat generation. That's why we aim to use one motor when trying to achieve the smallest structure possible.

Three Fingers

What is the fewest number of fingers you can have? If you consider only the act of grasping, just two fingers would be enough to do the job. However, workpieces come in many shapes, and they need to be grasped securely when being moved. To continue grasping various shapes securely, you need to have at least one additional finger. That's why there has to be three fingers even in the smallest structure.

Three Fingers per Motor

Even if there are three fingers, if those fingers are of a fixed shape like a three-jaw chuck, they cannot match their grip to the workpiece. That’s why a link mechanism is required to perform an articulated wrapping motion like human fingers. In addition, because there’s only one motor, the included link mechanism needs to cause the finger joints to bend during the stroke when power from the single motor actuates the three fingers. In order to achieve this complicated yet simple structure that converts one motor's rotation into linear motion and distributes that stroke through a link mechanism, the motor is also mounted using the trunnion structure that bears part of the link mechanism.

Adopting a SEED Actuator

Even if you are able to make the robot hand as small as possible, it means nothing if the control box is big. The SEED actuators developed by THK can be operated with SEED Driver, which is a compact modular motor driver that is only 20 mm square, so even the control system can be built into the hand unit.

Simple Controls

Ordinarily, the ability to grip and pinch various shapes would require complex controls. With SEED actuators, these functions can be achieved with a simple ON/OFF system.

The Birth of the General-Purpose Gripper TRX

This is how we arrived at the General-Purpose Gripper TRX, which is a highly compact universal gripper with one motor, three fingers with a link mechanism, and an integrated controller. Thanks to control provided by the SEED Driver, it only requires a power supply to run, with no need for a separate driver.