# AugLimb: Compact Robotic Limbs for Human Augmentation

Zeyu Ding1 Shogo Yoshida1 Toby Chong2
Tsukasa Fukusato2 Takuma Torii1 Haoran Xie1 Japan Advanced Institute of
Science and Technology1
The University of Tokyo2Japan<EMAIL_ADDRESS>
###### Abstract.

This work proposes a compact robotic limb, AugLimb111project homepage:
https://bit.ly/3mLYcgd, that can augment our body functions and support the
daily activities. AugLimb adopts the double-layer scissor unit for the
extendable mechanism which can achieve 2.5 times longer than the forearm
length. The proposed device can be mounted on the user’s upper arm, and
transform into compact state without obstruction to wearers. The proposed
device is lightweight with low burden exerted on the wearer. We developed the
prototype of AugLimb to demonstrate the proposed mechanisms. We believe that
the design methodology of AugLimb can facilitate human augmentation research
for practical use.

Figure 1. AugLimb robotic arm can transform from a compact size to an extended
length from step 1 to 6. We confirmed the usage of the developed prototype
mounted on user’s upper arm in both compact (a) and expanded states (b).

##  1\. Introduction

Wearable devices that enforce and augment our body are becoming pervasive
nowadays. To augment human ability using robotic technologies (Sasaki et al.,
2017; Xie et al., 2019), a wearable robotic limb is helpful in supporting the
daily activities as a third arm. In this work, we focus on the physical
augmentation with a compact robotic limb.

Figure 2. The proposed AugLimb device in compact state (a) and the expanded
state (b).

Previous works on robotic limbs are usually heavy and bulky, such as the
supernumerary robotic limb for workers (Bright, 2017). The user may feel
fatigue wearing these devices for long time usage, and the devices may cause
occlusion to user’s activities while not in usage. MetaLimbs proposed a pair
of robotic arms carried on the user’s back (Sasaki et al., 2017). However,
this device may require large volume. xLimb adopted the storable and
extendable mechanisms that reduce the burden exerted on the user (Ding et al.,
2021). In this work, we improve the controllability of robotic limb to larger
degrees of freedom (DOFs) and the extendable mechanism with a double-layer
scissor unit for stable and various system control.

In this work, we propose a compact robotic limb, AugLimb, that can transform
from a compact state to expanded state with quite long achievable range by
applying the extendable mechanism as shown in Figure 1. The main features of
AugLimb are compact storage and extendable function. AugLimb is compact in
idle status (Figure 1(a)) without interfere with the wearer’s daily
activities, and reach a far distance much longer than human arm (Figure 1(b)).

##  2\. Design and Implementation

### Device Design

Figure 2 shows the proposed robotic limb of AugLimb in compact and expanded
states. AugLimb has 7 DOFs and 1 extension unit. The whole joints include
shoulder, elbow, wrist, and gripper parts. The shoulder and wrist parts have
both rotational and twisting joints, shoulder-t and shoulder-r, wrist-t and
wrist-r, respectively. The gripper part includes an unit of extendable
mechanism with the extension joint, gripper and gripper-r joint for rotating
the gripper. The supplementary video shows more details of the device design
of AugLimb and its joint functions.

### Hardware Implementation

As shown in Figure 2(b), we used 5 servomotors and 4 direct current (DC) gear
motors in our hardware design. In our prototype design, we adopted GX3370BLS
motor for shoulder-r, DS3235SG motor for the shoulder-t, S53-20 motors for the
elbow and wrist-r, SG92R motor for the gripper, a DC encoder gear motor (6V
10-1000rpm) with reduction gearbox (reduction ration 1:130) for the wrist-t,
and GA12-N20 DC motors for the extension joints. Note that we used two DC
motors for the extension joints to increase the torque force. For reduce the
redundancy of robotic control, we did not implement the gripper-r joint in
current prototype. We used Prusa I3 MK3S 3D printer to fabricate the arm base,
shoulder, elbow, gripper and extension unit with PLA filament material.
Without the control unit, the net weight of our implemented device is 640g. We
used Arduino mega as control unit with 7 volts supply power.

### Extendable Mechanism

We adopt the double-layer scissor unit for the extendable mechanism to expand
the achievable range of the gripper joint. With the proposed mechanism, the
unit can be expanded to 250 mm, 3.6 times of the non-extension state (70 mm).
For the whole robotic limb design, the maximum reachable length from the pivot
of the base motor was 710 mm with the extended mode (630 mm without gripper).
Therefore, AugLimb can achieve 2.5 times than the forearm length of a male
adult (250 mm). Note that the gripper length is not included in measurement.

### Anticipated Applications

Figure 3 shows two examples of the anticipated applications with the proposed
AugLimb device. Due to the advantages of compact size and extension mechanism,
AugLimb could be useful for supporting various daily activities including
walking, cooking, and working environments.

Figure 3. AugLimb can be transformed into compact state while the user walks
through the narrow door (a), and can fetch the object far away in the cooking
scenario (b).

##  3\. Discussion

Automatic control of AugLimb from biological information is one issue to be
solved in near future. This study verified the system design with the
fabricated prototype which was controlled manually by the Wizard of Oz
approach. It is difficult to apply foot movement tracking (Sasaki et al.,
2017) for standing postures which are common in daily activities. The
potential solutions may acquire motion data from the upper-body parts such as
shoulder and wrist. The limited weight that AugLimb can lift can be improved
by increasing the payload through the motors adoption, structure and material
optimizations, such as metal and carbon fiber materials. Please find more
details of the proposed device in the introduction
video222https://youtu.be/WyTDA7tjCjM.

## References

  * (1)
  * Bright (2017) Lawrence Bright. 2017\.  _Supernumerary robotic limbs for human augmentation in overhead assembly tasks_.  Ph.D. Dissertation. Massachusetts Institute of Technology.  https://dspace.mit.edu/handle/1721.1/111770
  * Ding et al. (2021) Zeyu Ding, Shogo Yoshida, Takuma Torii, and Haoran Xie. 2021\.  XLimb: Wearable Robot Arm with Storable and Extendable Mechanisms. In _Proceedings of the 12th Augmented Human International Conference_ _(AH’21)_. ACM, New York, USA, 8:1–8:4.  https://doi.org/10.1145/3460881.3460936
  * Sasaki et al. (2017) Tomoya Sasaki, MHD Yamen Saraiji, Charith Lasantha Fernando, Kouta Minamizawa, and Masahiko Inami. 2017\.  MetaLimbs: Multiple Arms Interaction Metamorphism. In _ACM SIGGRAPH 2017 Emerging Technologies_. ACM, New York, USA, 16:1–16:2.  https://doi.org/10.1145/3084822.3084837
  * Xie et al. (2019) Haoran Xie, Kento Mitsuhashi, and Takuma Torii. 2019\.  Augmenting Human With a Tail. In _Proceedings of the 10th Augmented Human International Conference_ _(AH’19)_. ACM, New York, USA, 35:1–35:7.  https://doi.org/10.1145/3311823.3311847