Pop Up! : A Novel Technology of Shape Display of 3D Objects
Masashi Nakatani*1

Hiroyuki Kajimoto*2

Dairokou Sekighuchi*3

Naoki Kawakami*4

Susumu Tachi*5

The University of Tokyo
1 Introduction
Pop Up! is a novel visual + tactile display for presenting
touchable 3D shapes using a pin-rod matrix to convey visual
depth information. Due to its dense arrangement and long range ofmovement, it can display large-scale, dense objects such as humanfaces, geographical features and architectural structures. Theeffect is similar to a children’s "Pop up book," where a flat surface
transforms into a 3D form. Each pixel is composed of a simple
component shown in figure 1. The pin-rod is driven up applying
voltage to the actuator, and the pin-rod is driven down by coolingthe actuator with an air fan through a slit in each plastic pipe. Inaddition, the driving method is scalable so that displays of any
size can be constructed in the same way.
For the SIGGRAPH 2004 exhibition, we developed a shapedisplay composed of 1024 pin-rods with a 4mm pin interval. Eachpin-rod has a maximum stroke of 30mm, and the height can becontrolled within a 1mm accuracy.

2 Technical Details
To realize a shape display composed of many pin-rods forsophisticated applications, there are three requirements. The firstrequirement is speed. The pin-rod must move as fast as possible if
we want to display dynamical shapes such as facial expression.
The second requirement is density in order to present fine detail.
For example, the pin-rod interval must be at most 4 mm to display
a human face; otherwise, the displayed face could not express
subtle personal characteristics. We have tested this issue throughboth computer simulation and with a static pin-rod matrix (seeMPEG movie). The third requirement is the number of pin-rods.
As the pin-rod interval must be at most 4 mm, we need at least a
32 by 32 matrix of pin-rods to display our face, which means thatat least 1024 pin-rods must be actuated independently. From anengineering point of view, to achieve this number, each pin-rod
must be as simple and cost-efficient as possible.
To meet these challenges, we developed the following two coretechnical innovations. The first is the use of Coil-type ShapeMemory Alloy (C-SMA). Ordinary SMA is very small and thin,and it can produce a very strong force. Therefore, SMA has been
said to be a potential realization of artificial muscle. However,ordinary SMA does not have a long stroke, and the movement isquite slow, especially when it extends back its original length,
which is the main reason why it is generally avoided as anactuator. To improve its response rate, we chose to use C-SMA.
The diameter of the C-SMA is only 0.85mm, yet it can lift at least
40gf. The coil can be extended to twice its original length, andshrunk to its original length by heating. The coil-form enables
much faster cooling than previous SMAs, because of its large
surface area. Thanks to its thinness, speed, and simplicity, it is an
ideal actuator for our display.

The second innovation is the controlling actuator method andalgorithm. To actuate multiple actuators at the same time is thegreatest technical challenge for our display. For example, if weuse servomotors, the same number of control signals and pin-rods
is necessary to drive each actuator independently. As our goal isto drive displays with 32 by 32 pin-rods or more, this method isimpractical. Instead, we applied a “matrix drive” method, which iscommonly used in LCD display drivers. However, a simple
matrix drive method by itself is insufficient for this system inspeed performance. Therefore, we solve the optimization problemof time-scheduling, to determine how much time should be
assigned to each pin-rod. Pop Up! is designed to display 3Dobjects with a custom optimized controlling algorithm weinvented, which enables the display of shapes faster than a nonoptimized matrix drive method.

3 Future Works
One goal of our project is the realization of the "Face Phone" (seeMPEG movie and Figure 2). Such a device would display
dynamic rangefinder data obtained from a human face.
Conventional videoconference technology can convey vocal andvisual information, but this “Face Phone” can also convey a senseof existence, which helps our daily communication with others.
The ultimate goal is for Pop Up! to become a substitute orsupplement to the traditional LCD or CRT display, to enhance its
quality and modality as a 3D interface.

Figure 1: The configuration on single pixel.

*1e-mail: nakatani@star.t.u-tokyo.ac.jp
e-mail: kaji@star.t.u-tokyo.ac.jp*3e-mail: dairoku@star.t.u-tokyo.ac.jp*4e-mail: kawakami@star.t.u-tokyo.ac.jp*5e-mail: tachi@star.t.u-tokyo.ac.jp*2

Figure 2 : The concept of “Face Phone.”