NewTechnology

Application Examples of the Wrist Joint Module“i-WRISTTM”

Yuzuru TANAKA*
NTN developed an angle control equipment system applying a parallel
link mechanism, a constant velocity joint1)-7). We started mass production
under the product name of the “i-WRISTTM” in August 20188).
We have improved its functions to meet the needs of customers and havelaunched it on the market with the target of automating and reducing
manual work9). The features of the i-WRISTTM like “high-speed anglecontrol” are useful in the appearance inspection process of complexshaped parts. We would like to introduce application examples that showsuch advantageous features of the i-WRISTTM.

1. Introduction
Due to the reduction in the working population,
aging of skilled workers, and rise in personnel
expenses, the range of application for robots has
spread from work mostly involving tasks that placeda heavy load on operators and extremely dangerous
work, such as transporting heavy objects and welding,to more detailed manual labor work. Among thesemore detailed jobs, appearance inspection still relies
heavily on manual labor, and there is an increased
demand to automate this type of work. However,conventional robots cannot achieve the speedof visual checks performed by humans, and theautomation of appearance inspection for complex
shaped parts is particularly lagging.
NTN has proposed the application of Wrist Joint
Module “i-WRISTTM” to automate tasks handled byhumans. i-WRISTTM has received high praise for its
strength in “high-speed angle control”, and examples
of its use in projects to automate visual inspection
have increased.

2. i-WRISTTM overview
i-WRISTTM is a robotic module product that achievessmooth movement like a human wrist. Fig. 1 showsa schematic drawing of the i-WRISTTM unit. The
i-WRISTTM unit comprises a parallel link mechanismand drive mechanism. The drive mechanism
determines angle orientation in 2degrees of freedom(bending angle and swing angle) at the parallel
link mechanism for high-speed and high precision
positioning within hemispherical areas. Furthermore,
cables can be passed through the internal space of theparallel link mechanism, so the cables do not become
twisted even when swing operation is repeated in thesame direction.

Fig. 1 Schematic drawing of i-WRISTTM unit

3. Features of i-WRISTTM in use at theproduction site
The use of robots at the production site poses
problems for some managers who give comments
such as “we installed robots but are not satisfied
with the cycle time”, “robots are difficult to operate
and hard to master” and “we have no space to installrobots.” To solve these problems, NTN proposes aconfiguration9) that combines i-WRISTTM with a linear
actuator or rotation actuator. The features of this areshown below.
(1) Fast motion
The moment of inertia at the entire movablesection is small, and the robot can move to the target
orientation along the shortest route. Therefore, thissetup can be particularly effective for work that
requires fine movement, something that conventional
robots do not do well.
(2) Easy of use
Even operators who do not have expert knowledgeof robot language can easily operate this setup using
a dedicated console.

* Robotics & Sensing Engineering Dept., Industrial Business Headquarters

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(3) No singularity point
There is no need to create an operation program
to avoid the singularity point, as is the case witharticulated robots.
(4) Offline teaching
NTN provides a PC-based teaching tool to specify
points on a 3D model and configure operating
patterns9).

resolved using the features of i-WRISTTM. For example,
as shown in Fig. 3, inspection processes that haveso far required the use of two robots can now beconfigured using a single i-WRISTTM unit, and this has
been evaluated as achieving the required cycle timeand has been adopted for use. Below introduces more
specific examples of the application in appearance
inspection.

(5) Space-saving
In combination with a linear actuator or rotation
actuator, the machine can be compactly configured,
which allows this setup to be installed in a space
where a operator worked9).
Fig. 2 shows examples of application for i-WRISTTM.
Among such applications, i-WRISTTM is often used
in appearance inspection machines equipped withcameras and lighting. An example of this is shown
below.

Appearance inspection

Grease dispensing

Fig. 2 Example of applications for i-WRISTTM

4. Example of applications for i-WRISTTM
in appearance inspection
During appearance inspection of workpieces thathave a 3D shape or complex shape, such as castingparts and resin molded parts, humans can quickly andskillfully visual inspection multiple locations of theworkpiece from various angles while changing how
lighting is shone onto the workpiece and the angleof the workpiece. This type of high-speed inspection
is exceedingly difficult to automate. However, many
examples exist in which this difficulty has been(a) With conventional robots(b) With i-WRISTTM

Fig. 3 Example of application at the production site
4.1 Example of application for casting parts
During appearance inspection of small castingparts, such as for an automotive compressor as
shown in Fig. 4 (a), appearance inspection of 0.2
seconds per single point -- about 2.5 times the speedof conventional robots -- was achieved. Fig. 5 shows
an example of the configuration for this system.
This configuration involves mounting a camera onto
i-WRISTTM and controlling the angle, while a rotation
actuator and linear actuators are used to position
the workpiece. The rotation actuator rotates theworkpiece while images are captured from multiple
directions. This enables high-speed inspection for
defects such as surface scratches, dents, and residualdebris inside bore holes. This configuration can also
make the machine more compact.
During appearance inspection of large casting parts
such as for an engine block or transmission case as
shown in Fig. 4 (b), appearance inspection of 0.3
seconds per single point was achieved. Fig. 6 shows
an example of the configuration for this system.
This configuration involves mounting a camera
onto i-WRISTTM installed at an incline and using arotation actuator and linear actuators to position theworkpiece. Installing i-WRISTTM at an incline enables
images to be taken of the workpiece while looking up
at the workpiece from below. This enables high-speed
inspection for defects such as scratches on unevensurfaces at the side of the workpiece, dents, andresidual debris inside bore holes.

(a) Small casting part(b) Large casting partFig. 4 Casting parts

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Application Examples of the Wrist Joint Module “i-WRISTTM”

Fig. 5 System configuration example (1)Fig. 6 System configuration example (2)4.2 Example of application for automotive resin
molded parts
During appearance inspection of automotive resin
molded parts integrated with various sensors asshown in Fig. 7, visual inspection of 0.3 seconds per
single point was achieved. Fig. 8 shows an example ofthe configuration for this system. This configuration
involves fixing the camera and lighting while a chuck
mounted onto i-WRISTTM holds the workpiece. The
workpiece is positioned using i-WRISTTM, a linear
actuator and a rotation actuator. The use of a rotation
actuator achieves a compact system configurationthat can minutely change the positioning of theworkpiece while rotating it for a single revolution at
the same position. This configuration enables thesystem to inspect the appearance of surface (forscratches, bubbles and burrs) and check whether any
connector pins and sensor parts are missing.

Fig. 7 Resin molded part104

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Fig. 8 System configuration example (3)4.3 Example of application for automotive electroniccontrol unit
With the electronification of automobiles,
examples of appearance inspection have increased
for automotive electronic control units, such as gearboxes integrated with electronic circuit boards asshown in Fig. 9. This type of unit has sections whereimages are difficult to capture, such as the back ofcircuit boards, so a person visually inspects blind spotsthat are difficult to see while changing the angle. The
system configuration shown in Fig. 6 enables images
to be captured of electronic control units, including
the back of circuit boards from multiple directions.
The illumination angle can be finely adjusted onto thecircuit board using i-WRISTTM so that light shines onto
blind spots. This enables inspection of blind spots atthe back of the circuit board (the soldered surface) as
shown in Fig. 10. In this example an inspection speedof 0.3 seconds per single point was achieved to checkfor missing parts on electronic circuit boards, andfor appearance defects on the resin surface such as
scratches, dents, and burrs.

Blind spot
(Back of circuitboard)

Fig. 9 Electronic control unit Fig. 10 Example of captured image(back of circuit board)
4.4 Through-hole and screw-hole internal inspection
There is also a high demand for automating
inspection of burrs and residual debris inside throughholes and screw-holes. Using the pivot movement of
the i-WRISTTM enables the angle to be changed while
maintaining working distance from the camera to
the reference point by linked i-WRISTTM and linear
actuators. Using this action enables images to becaptured as shown in Fig. 11. This can make it easy toinspect the entire inside diameter surface of a hole.

and create examples of applications to contribute toautomating and optimizing the production site andstabilize quality.

Reference point

Fig. 11 Pivot movement

5. Efforts to increase the range ofapplication for i-WRISTTM
Amid the launch of i-WRISTTM to the market, we
received praise for i-WRISTTM high speed operation, andits excellent ability to work without singularity points,
which is a challenge for conventional robots. At thesame time, we received many requests for i-WRISTTM tohandle similar payloads as conventional robots and haveinvestigated methods to achieve this.
Until now, maximum load capacity was restricted to1 kg so that i-WRISTTM could be used at high speed.
However, we developed a new grade that increases
the maximum payload to 3 kg by establishing a modethat optimizes the control method to match the load
capacity. As a result, it is now possible to mount largescale lighting and multiple lighting onto i-WRISTTM forappearance inspection. Using large-scale lighting enables
images to be captured over a large area in a single shot,
and this reduces the number of inspection points, whichleads to a shorter cycle time. Furthermore, using multiple
lighting increases the variation of how lighting can beshone onto a work piece being inspected. This provides
support for work pieces that are difficult to inspect.
In addition to appearance inspection applications,i-WRISTTM can be applied to such as the deburring
process in which the machining load acts on the end
effector, and the welding process in which the end
effector weight is large.

6. Summary
This paper introduced examples of appearance
inspection using high-speed angle control, which is astrength of i-WRISTTM. Using i-WRISTTM can replacesight checks that are difficult to automate and achievea cycle time that cannot otherwise be achieved withconventional robots.
In the future, there will be greater demand forautomating complex work performed by humans, suchas deburring and assembly to accompany the decreasein the working population. i-WRISTTM introduced here is arobotic module product that can achieve automation ofmanual work at a work speed and smooth movement likehuman hands. NTN will continue to improve performance

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Photo of author

Yuzuru TANAKA
Robotics & Sensing
Engineering Dept.,
Industrial Business
Headquarters
NTN TECHNICAL REVIEW No.89

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