DESIGNING A NEW TOY TO FIT OTHER TOY PIECES- A shape-matching toy design based on existing building blocks 1(a) Building blocks

Yuki IGARASHI1 and Hiromasa SUZUKI2The University of Tokyo, Japan / JSPS research fellow
2
The University of Tokyo, Japan(b) Input photograph(c) The user designs a toyusing sketching interface(d) Traced outlines(e) block-shape matching toyFigure 1: Overview of our method
ABSTRACT: Shape-matching toys are popular items for infants, and consist of boxes with manyholes in different shapes along with corresponding blocks of the same shapes. To play with the toy,
an infant finds and inserts a block matching the shape of a particular hole. It is very difficult todesign such toys because the toy body Onew must closely fit the shape of the existing blocks Oexisting.
The designer usually takes the measurements of the blocks Oexisting and draws corresponding featuresizes, then makes a construction diagram for the toy body Onew. We propose a computer-based
method for novices to enable the design of a new toy to fit other toy pieces. The method involves
making a construction diagram for Onew on a photograph of the blocks Oexisting using a computer.
The user first takes a photograph of the blocks on a checkerboard, then designs the form of the new
toy Onew on the photograph using a sketching interface. From the photograph on the checkerboard,
the system automatically fits the designed toy Onew to the actual measurements and exports theresults in vector form. The system supports SVG and DXF formats. Finally, the user cuts the shapes
from a wooden board using a cutting plotter or laser printer.
Keywords: design, user interface, craft………………………………………………………………………………………………………....
1. INTRODUCTION
Shape-matching toys are popular items for
infants, and consist of boxes with many holes
in different shapes along with corresponding
blocks of the same shapes. To play with thetoy, an infant finds and inserts a blockmatching the shape of a particular hole. It isdifficult to design new shape-matching toys
based on existing blocks. We assume that theuser performs such design as shown in Figure

1 (e) based on existing building blocks likethose shown in Figure 1 (a). The constructionof the toy body can be roughly divided into
three steps: gather the parts, lay them out on awooden board and trace them using a pencil,
and saw the wooden board. This manual
method is straightforward, but errors cannot
be rectified and it is also unsuitable for mass
production.
Accordingly, we propose the use of a lasercutter (e.g., Commax Laser System [1]) or a
cutting plotter (e.g., Craft ROBO [2]). Today,
services are available that allow the user tosend a vector dataset to a company and havethe corresponding wooden board returned tothem [3]. This means that the user can obtaina new toy body simply by providing shapedata in vector form. The construction of a toy
using a laser cutter can be roughly divided
into five steps: gather the parts, measure them,
implement design using existing software thatallows the user to input actual measurements(e.g., Adobe Illustrator [4]), output the designin vector form and input the data to the laser
cutter. However, the labor-intensive nature ofthis process means that it is very difficult todesign a new toy body Onew to fit existing
blocks Oexisting. The user usually takes themeasurements of the blocks Oexisting and draws
corresponding feature sizes, then creates aconstruction diagram for the toy body Onew.

The user first prints a checkerboard and takes
a photograph of the existing building blocks
Oexisting on it. The checkerboard consists ofsquares with 10-mm edges.

(a) Input photographTo enable the design of new toys based on
existing pieces and other similar products, wepropose a computer-based method for novices
to enable the design of a new toy body to fit
existing toy blocks. The method involves
creating a construction diagram for Onew on a
photograph of the blocks Oexisting using acomputer (Fig. 1). The user first takes aphotograph of the existing blocks Oexisting on acheckerboard, then designs the form of thenew body Onew on the photograph using asketching interface. From the photograph on
the checkerboard, the system automaticallyfits the designed body Onew to the actual
measurements and exports the results invector form. The system supports SVG andDXF formats. Finally, the user cuts the shapes
from a real wooden board using a cutting
plotter or laser printer.

(b) Outlines traced by the user(e) Edge extraction(c) Traced outlines(f) Marking grids
manually(d) Conversion to DXF(g) Adjustment tofull scale(h) Cutting using laser plotter

Figure 2: Overview of our algorithm
The user draws free-form strokes on the input
photograph to trace the outlines of the blocks
using the sketching interface (Fig. 2 (b)). The
system also provides a number of basic
shapes (line, rectangle and ellipse), andexports the user-input strokes in vector formas shown in Fig. 2 (c). In line mode,

2. SYSTEM OVERVIEW
Figure 1 shows a real toy made using theproposed method. Our goal was to design a
new shape-matching toy body (Fig. 1 (e))
from existing building blocks (Fig. 1 (a)).
Figure 2 shows the proposed user interface.
2

input image, then inverts each image and adds
it. The system finally obtains Image I’.

user-input strokes can be made to snap toexisting strokes by holding down the Shift
key. In rectangle mode, the user can draw
squares by holding down the Shift key. Inellipse mode, the user can draw circles byholding down the Shift key. The system
finally exports the use-input strokes in vector
form as shown in Figure 2 (c).

Input Image I

The checkerboard is used for scale adjustment.
Although various methods have been
proposed for feature point extraction in 2D [5],[6], [7], no method currently enables precise
extraction. Accordingly, we adopt manual
input by the user. The system first extracts thecheckerboard grid using edge detection, andthe user can easily mark the corners of thegrid using the extracted edge image (Fig. 2(e)). The user has to mark corners at morethan two unbroken points (Fig. 2 (f)). Thesystem calculates the ratio r of the image tothe actual size (Fig. 2 (g)).

-1 0 1-2 0 2-1 0 1

1 0 -1
2 0 -2
1 0 -1-1 -2 -1
0 0 0
1 2 1

1 2 1
0 0 0-1 -2 -1

INVERSE

INVERSE

INVERSE

INVERSEOROROR

Edge detection Image I’

The system exports the designed shape(Figure 2 (c)) in vector form using the ratio r,and supports SVG and DXF formats. The usercuts the shapes from a real wooden board
using a laser printer [1] or a cutting plotter [2].
In this way, the user can design a toy body
Onew to fit existing blocks Oexisting.

Figure 3: Edge detection algorithm
3.2 Adjustment to actual scale
After edge detection, the user marks thecorners of the grid manually as shown in
Figure 2 (f). The user has to mark corners
connecting one side of a slot on thecheckerboard (Figure 2 (f)). The system thencomputes the average distance for the sides on
the grid. Specifically, it first finds the closest
marker point for each point Pi and calculates
the distance di to its closest point. The systemthen calculates the average value of thesecomputed distances.

3. ALGORITHM
Our prototype system was implemented as aJava program with the user-input strokes
represented as polylines. The system employs
internal vector representation.
3.1 Edge detection
Edge detection here uses a convolution filter.
The system first transforms the input image
into gray-scale. To obtain the output shown as
Image I’ (Figure 3, bottom) from Image I(Figure 3, top), we prepare four Sobel
operators (two for the perpendicular direction
and two for the horizontal direction). Thesystem first applies each Sobel operator to the4. RESULTS
The system runs in real time on a 1.1-GHz
Pentium-M
PC.
We
designed
twoshape-fitting toys using our approach andcreated real toys, one of which is shown in
Figure 4. This example shows the design of anew block-shape-matching toy body based on3

existing building blocks. The other is shownin Figure 5. This example shows the design ofa new puzzle cover based on existing pieces.
The holes of the cover designed fit therelevant positions on the base puzzle. We
export the final design data in DXF using oursystem and perform laser cutting [1].

Figure 4: Example of designing ashape-matching toy body based on existingbuilding blocks using our method
5. EVALUATION
We tried the system with three test-users, who
designed a shape-matching toy as shown inFig. 1. Graph 1 shows a comparison of theapproach and its implementation using
existing software (Adobe Illustrator). In ourmethod, the user first takes a photograph ofthe building blocks Oexisting on a checkerboard,then draws strokes to create a diagram for theshape-matching toy body O n e w on thephotograph and marks its corners. With theexisting approach, the user first measures thebuilding blocks O e x i s t i n g and draws aconstruction diagram for the shape-matching
toy body O new . We skip the remaining
processes of exporting the designed shape invector form and formation using a cutting
plotter, as both methods follow the same

Figure 5: Example of a puzzle cover design
based on an existing puzzle.
process after shape design. As indicated by
the results in Graph 1, new toy design using
our method is relatively easy.
We also check the number of markers thesystem needs. It is only necessary to mark 5 –6 points according to the results of the user
study as shown in Fig. 4. This took about 10 –13 seconds, and the test-users reported thatthey found the system easy to use.

4Graph 1: Comparison of timing datameasurement using our method.

User 3 (Illustrator)

Photo capture
DesignMarking
Measurement
LayoutUser 3 (our method)
User 2 (Illustrator)
User 2 (our method)

This research shows that an amateur user candesign a new shape-matching object (e.g., atoy) based on existing objects using acomputer. This is very helpful for
non-professional users seeking to design
functioning real-world objects. We plan to
apply this approach to various other problems.
As an example of extension in 3D usage, auser may wish to perform design to replace abroken handle on an existing teapot.

User 1 (Illustrator)
User 1 (our method)
0200

400600

800

1000
1200
Time (sec.)

1400

1600

1800

2000

0.8

Marker distance

0.70.60.5
0.4
0.3

User 1
User 2User 30.2
0.1

ACKNOWLEDGMENTS
We would like to thank Prof. Jun Mitani ofTsukuba University, Japan, for providing thesource code for DXF export. We are also
grateful to the participants of the user study,
and to the JST ERATO Igarashi Design
Interface project for providing the laser cutter
used here. This work was partially supported
by a Grant-in-Aid for JSPS Fellows.

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Number of markers

Figure 6: Number of markers
6. CONCLUSION AND FUTURE WORKWe propose a computer-based method fornovices to enable the design of new toy
bodies to fit existing pieces. The approachallows simple design of shape-matching toys
through tracing with a pencil. From thephotograph on the checkerboard, the system
automatically fits the designed toy body Onew
to the actual measurements taken.

REFERENCES[1] Commax Co., Ltd., Commax Laser System
Value Direct 7050-60W.
[2] GRAPHTEC, CraftROBO.
http://www.graphteccorp.com/craftrobo/.
[3] Pololu Robotics & Electronics, Custom
Laser Cutting.
http://www.customlasercutting.com/[4] Adobe Illustrator.
[5] Carlson, S., Sketch based coding of graylevel images. Signal Processing, Vol. 15,pp. 57-83 (1988).
[6] Elder, J. H. and Goldberg, R. M., Image
Editing in the Contour Domain. IEEETrans. on Pattern Analysis and MachineIntelligence, 23 (3), pp. 291-296, 2001.
[7] Bradski, G., Kaehler, A. (2008), Learning
OpenCV: Computer Vision with theOpenCV Library.

One limitation of this method is that care isrequired with taller pieces. For instance, if aphotograph is taken from a height of 40 cm
and the target toy is 4 cm tall, the shapedesigned using the system is 10% smaller
than the user requires. This problem wasresolved here by taking the photograph from ahigher position. Although various methods
have been proposed for 3D modeling frommultiple images, they remain very difficult fornovices to use as they require image
calibration and other advanced techniques. It
is difficult to construct a faithful 3D modelfrom a single image, but the results here
indicate the feasibility of practical5

ABOUT THE AUTHORS
1. Yuki IGARASHI is a Ph.D student at theUniversity of Tokyo and a JSPS research
fellow. Contact details: yukim@acm.org;
Graduate School of Engineering, TheUniversity of Tokyo, 4-6-1 Komaba,
Meguro-ku, 153-8904 Tokyo, Japan
2. Hiromasa SUZUKI Dr.Eng. is a professor
at the University of Tokyo, Japan. Contact
details: suzuki@den.rcast.u-tokyo.ac.jp;
Graduate School of Engineering, The
University of Tokyo, 4-6-1 Komaba,
Meguro-ku, 153-8904 Tokyo, Japan6