Particle Mechanical Constraint
(Particle Jamming)

What is Particle Mechanical Constraint?

Particle mechanical constraint (PMC) is a light-weight mechanical element that can vary the stiffness by changing the inside air pressure. The structure is very simple. PMC is a bag containing beads (e.g. Styrofoam beads) so that it can be freely elongated, compressed, bent, twisted, or otherwise deformed into any shape. Evacuation of the inside air makes the PMC rigid so that it maintains the shape in the same way that vacuum sealing for coffee beans makes the package rigid. The PMC has recently been called a jamming technology by other researchers. It is suitable for a wearable human interface because it is light-weight and soft.

Structure

PMC can be developed in any shape. However, a gimmick is required to maintain the stiffness in any shape. Figure 1 depicts a structure of a cylinder-type PMC. Styrofoam beads are enveloped in a vinyl chloride tube. The PMC is airtight, and the inside air moves only through an air hole at one end. The area inside the tube is divided into several compartments by breathable cloth discs so that the beads are distributed uniformly regardless of how the PMC is reshaped. In case the beads are distributed unevenly, a deep wrinkle occurs and loses the stiffness (see Figure 2). Resin rings fixed on cloth disks also contribute to prevent deep wrinkles.


Figure 1. Structure of a cylinder-type PMC


Figure 2. Loss of stiffnesss due to a deep wrinkle

Mechanical properties

PMC can be developed in any shape. However, a gimmick is required to maintain the stiffness in any shape. Figure 1 depicts a structure of a cylinder-type PMC. Styrofoam beads are enveloped in a vinyl chloride tube. The PMC is airtight, and the inside air moves only through an air hole at one end. The area inside the tube is divided into several compartments by breathable cloth discs so that the beads are distributed uniformly regardless of how the PMC is reshaped. In case the beads are distributed unevenly, a deep wrinkle occurs and loses the stiffness (see Figure 2). Resin rings fixed on cloth disks also contribute to prevent deep wrinkles.


Figure 3. Stiffness of a cylinder-type PMC [1]

A vacuum control system

Figure 4 shows a vacuum control system with an electric vacuum pump and two electro-pneumatic proportional valves that each controls a cross-sectional area for the air flow. The vacuum pump evacuates the air inside the PMC through valve A. Opening valve B allows air from the atmosphere into the PMC. The air pressure inside the PMC can be controlled by the ratio of the two cross-sectional areas. This system can control the air pressure faster than an electric vacuum regulator on the market. When a quick response is not needed, the air pressure can also be controlled simply by a hand vacuum pump.


Figure 4. A vacuum control system [1]

Wearable force display

Figure 5 depicts a wearable force display. One end of a cylinder-type PMC is fixed to the under-arm of the operator, and the other end was attached to a glove. The operator can feel the force sensation through the glove, such as the sensation of moving the hand in water with viscosity and the sensation of touching a wall.


Figure 5. A wearable force display


Figure 6. A virtual boxing

Upper-arm functional orthosis

The orthosis depicted in Figure 7 can fix the elbow and shoulder movements by the two PMCs. When it is used for training, the training load can be controlled by changing the stiffness of the PMCs.


Figure 7. Upper-arm functional orthosis

About this study

This study was funded by JSPS research for the future program (96P00804) and Industrial Technology Research Grant Program.

Examples (movies)

Upper-arm orthosis
Hand orthosis
Plate-type PMC
Cylinder-type PMC
Water bag with PMC
Water bag with PMC, like a dough
Active PMC. Bellows inside the PMC work as an pneumatic actuator.
A cast developped by an articulation-type mechanical constraint [2]
Hammmer and put a load on the cast
An articulation-type mechanical constraint

References

  • [1]Takashi Mitsuda, Sachiko Kuge, Masato Wakabayashi, Sadao Kawamura, Wearable force display using a Particle Mechanical Constraint, Presence, Vol.11, No.6, pp.569-577, 2002.
    doi:10.1162/105474602321050703
    pdf (This article was published by MIT Press Journal.)
  • [2]Takashi Mitsuda, Norichika Matsuo, Shape Stabilizer Using an Articulation-type Passive Element, Japan Fluid Power System Society Int. Symp. on Fluid Power, pp.723-727, 2005Nov.(Tsukuba).
    doi:10.5739/isfp.2005.722