Modular Soft Robots (MSRs)

Suggested Readings

[2020, Review] Modular Soft Robotics: Modular Units, Connection Mechanisms, and Applications (pdf)

[2007] Modular Self-Reconfigurable Robot Systems. Challenges and Opportunities for the Future

[2020, Thesis] A New Paradigm in Reconfigurable Robotics

[2012, Review] A Modular Approach to Soft Robots (Onal, Rus)

Nonlinear Modeling and Docking Tests of a Soft Modular Robot

Vacuum‐Powered Soft Pneumatic Twisting Actuators to Empower New Capabilities for Soft Robots

Modular assembly of soft deployable structures and robots

[Vacuubes] A Vacuum-Based Bonding Mechanism for Modular Robotics

Additional:

https://www.wikiwand.com/en/Self-reconfiguring_modular_robot#

Overview of Modular Soft Robots

Pros

+ Versatility 

+ Robustness  - modular upgrades & repairs

+ Low cost for manufacturing & maintenance

+ Adaptability to changing task & environments

+ Ease of repair by changing only damaged modules

+ Ease of transport & storage (e.g Space Launches)

+ Scalable

+ A small set of modules can enable infinite morphologies

Cons

- Complex and time-consuming to design

- Higher cost than application-specific soft robots

- Still in their infancy

- Couplings are most critical

- Couplings require custom design

- Choice of couplings still very limited.

- More complex to control than app-specific SRs

- Performance tradeoffs compared to nonmodular

Ful list of Pros & Cons of modular designs in the Modularity Resource Guide.

Capabilities 

- Adaptation to new Tasks and Environments

- Self Assembly

- Self Repair

- Reconfigurability

- Reusability of modules

- Fit into confined spaces

- High packing density when disassembled

Applications

- Medical, Surgical, Implantable 

- Home assistance (a modular chain manipulator)

- Physical representation of virtual objects

- Temporary housing structures beyond earth

- Terrain exploration

- Search and Rescue

- Minimally invasive surgery

- Safe human-robot interaction

Levels of Configurability

Configurable [48-67]

The parts are designed for a specific configuration or application

[msr] modular gripper.png

Modular Gripper

paper

Deep-sea Arm.png

Deep-sea Arm

video, pdf

beehive continuum manipulator.jpeg

Cintinuum Manipulator
pdf

[msr] Jellifish Robot.png

Jellyfish Robot

paper

[msr] implantable.png

Implantable Soft Robotics

pdf

[msr] modular sleeve.gif
[msr] surgical manipulator.png

Surgical Manipulator

paper1 paper2

[msr] Soft Robotic Snake.png

Modular Snake

pdf

[msr] 2D manipulator.png
[msr] wormbot.png

Voice Coil WormBot

video, pdf

Reconfigurable [47,68-87]

Capable of repeated structural or functional transformations.

Consist of homogeneous or heterogeneous units

vacuum.png

Vacuum Twist

paper paper Video

[msr] CMMWorm.png

CMMWorm

paper Video1, Video2PDF

[msr] V-SPA.png

V-SPA
PDF, PDF, Video

[msr] SoBL.png

Soft Robotic Blocks

paper video

[msr] morphIO.png

MorphIO

video pdf

[msr] Reconfigurable.png

Dockable Robot

paper

[msr] Modular Approch.png

Modular Approach

paper pdf

[msr] DeployBot.gif

DeployBot

paper paper video, video

[msr] inflatibits.png

Inflatibits

pdf video

[msr] soft lego.png

Soft LEGO

paper video

[msr] Click-e-Bricks.png

Click-e-Bricks

paper video

[msr] Elastomeric Tiles.png

Elastomeric Tiles

paper video

[msr] starfish.png

Starfish SMA Actuated

paper

[msr] Arthrobots.jpeg

Arthrobots

paper video

placeholder.png

ttt

paper video

ttt

paper video

Self-Reconfigurable [88,89]

Capable to achieving various morphologies automatically.

[Modular Soft Robotics] Omnidirectional

Caterpillar

video, paper

[msr] SoftCubes.png
placeholder.png
placeholder.png

SoftCubes

paper paper video

Architecture Types

Reconfigurable robots are classified into three types by the geometric arrangements of their units, Some are hybrids. 

Mobile Architecture

The individual modules are mobile and can attach individually

+ Modules can be physically disconnected but operate

as a single unit together.

+ Enables applications like self assembly and swarms.

- Modules are complex and expensive

Lattice Architecture

Modules are arranged and connected in some regular, 2D or 3D pattern, such as a simple cubic or hexagonal grid

+ Control & Motion can be executed in parallel

+ Easily scaled

- Movies can only be at discrete locations on the lattice

Chain Architecture

The modules connect to each other as a chain topology. The underlying structure is serial.

+ Folding is possible

+ Versatile in locomotion patterns

+ Connectable in 2D or 3D patterns

- Computationally demanding

- Difficult to control

Coupling Mechanisms & Interconnects

The connection mechanism between modules is the most critical part for modular systems with physically-connected modules. They determines factors such as range of motion, capabilities, efficiency, and overall size of a modular robot. A variety of connection types are possible between modules, each with its oen pros and cons, and there is not one best solution. 

  • Desirable Properties

    • Small Size

    • High Mechanical Strength under all loading scenarios

    • Information Transmission Capability

    • Power Transmission Capability

    • Reversibility & Repeatability

    • Ease & Speed of connection / disconnection

    • Self-Alignment

    • Very low or no power consumption

    • Orientation invariance & Genderlessness

    • Unilateral instead of bilateral actuation

    • Compliant rather than rigid

    • Low cost

Mechanical

Pros

+ Most common with high diversity

+ High reliability

+ Alignment precision

+ Self-alignment possible

+ High connection strength

Cons

- Typically large and bulky

- Difficult to detach

Rigid

+ 3D Printable

+ Parts readily available

- Severely reduced compliance & adaptability

- Increase the mechanical / structural complexity

[connector] Modular Robotic Wrist.png

Gendered

paper

[connector] Legris + 3D print.png

Legris Push-In Fitting

video, pdf

[connector] snap-lock.png

Snap Lock

pdf

[connector] v-spa.png

Electrical & Pneumatic

pdf, pdf, video

[connector] screws & spacers.png

Screws & Spacers

pdf

Soft

+ Maintain compliance of the soft robot

- Can't withstand high pressures or forces

- Virtually no examples in the literature

- Fully custom made

[connector] soft bystable.png

Bystable

video

Magnetic

Pros

​+ Easy attachment

+ Easy manual detashment

+ Self aligning

+ Conductive

+ Genderless & Orientation Invariant

Cons

- Reduce compliance of robot

Permanent Magnets

+ No power required

+ Very compact

+ Attachment to/of other metal parts possible

+ Easily combined with other actuators (Motors, SMA)

+ Suitable for submerged applications

- Disconnect requires extra actuation

- Misalignment or disconnection under load

[connector] Magnet with hole.png

Magnet with hole

paper

[connector] magnet.png

DeployBot

paper video, video

[connector] Soft Modular Robotic Cubes.p
[connector] Caterpillar.png

Reconfigurable Caterpillar

paper, video

[connector] magnet.png

Multiple Magnets

paper

placeholder.png

Placeholder

placeholder.png

Placeholder

placeholder.png

Placeholder

Electromagnets

+ Auto Connect & Disconnect possible

- Continuous power consumption during hold

- Sufficient space required

Electropermanent Magnet

+ Low power; used only for state change

+ Maintain state without power

- Expensive

- Custom fabrication required

Adhesive

Pros

+ Minimum spacing requirements

+ High connection strength

+ Low complexity

+ Genderless & orientation invariant

Cons

- slow connection & disconnection

- accurate alignment needed

Self-soldering

+ Low melt point at 62°C for Field's Alloy

+ Easily manufacturable by PCB fabricators

+ Small & Lightweight (2g, 3mm thick)

+ Programmable / Reversable

+ Conductive

- Not compliant, but can be made with flex PCBs

- Unsuitable for underwater applications

- Slow - 10s heating; 30s cooling

- Prone to corrosion

- Low durability (100+ cycles before failure)

Self-Soldering connector.png

Self-Soldering

Active Freeze (via peltier devices)

+ Low melt point at 62°C for Field's Alloy

+ Easily manufacturable by PCB fabricators

+ Small & Lightweight (2g, 3mm thick)

+ Programmable / Reversable

+ Conductive

- Not compliant, but can be made with flex PCBs

- Unsuitable for underwater applications

- Slow - 10s heating; 30s cooling

- Prone to corrosion

- Low durability (100+ cycles before failure)

Hot-melt Adhesives / hot glue (HMAs)  [135]

+ Connection & Disconnection possible

+ Nonsticky, viscoelastic solid at 25◦C

+ Heating/Cooling can be done locally or globally

- Slow

- Heating Mechanism required

- HMA Applica

- Cooling through natural heat dissipation, but active cooling is possible.

  • At room temperature (Tr around 25◦C), the material is an viscoelastic solid with no adhesiveness, thus unable to form new bonds. But existing connections are maintained with high bonding strength.

  • At softening-point temperatures Ts, the material starts to become visco-plastic and adhesive. The bond is drastically weakened, and maintain an established connection becomes difficult.

  • At melting point temperature Tm (generally 150◦C), the  the material transforms into a low-viscosity fluid.

NOTE: Ts and Tm vary depending on the ingredients of HMAs, and they are generally temperature ranges.

Electrostatic Adhesion [136]

+ Connection & Disconnection possible

- High voltage required

Glue / Silicone / Tape

+ Leakproof

+ No additional structures needed

+ Easy to apply

+ Dovetail joints can increase bonding area

[83]

- Difficult or impossible to disconnect

- Compliance is maintained

- Bonding strength proportional to bonded area

[connector] glued.png

Silicone Adhesion

pdf

[msr] 2D manipulator.png
[connector] Dovetail Joints.png

Dovetail Joints

pdf

[connector] Arthrobots.png

Arthrobots

pdf

Pneumatic (Vacuum)

Pros

+ Easy connection and disconnection

+ Automatic alignment possible

+ High connection strength

+ Low complexity

+ Can use the robot's pneumatic driver

Cons

- accurate alignment needed for good connection

- some designs prone to misalignment 

- extra pump may be required

- nonconductive

Vacuubes.png

Vacuubes

vacuum.png

Artificial Twisting Muscles

paper paper Video