Fingerprint Sensor TestingUsing Force Feedback Control

Viktor Johansson

Dep. Automatic Control, Lund Universityviktor.johansson@live.se

August 25, 2016

Abstract

Testing and validation of fingerprint sensors with human labor are time consuming, costly and lack thespeed, accuracy and repeatability required for sufficient results. In this article a brief introduction of anautomated solution with a robot that solves these problems is presented.

I. Introduction

The result of the thesis [2] shows that itis possible to automate testing and val-idation of fingerprint sensors using an

industrial robot and a force sensor.Advantages such as increased productivity,

better product quality and lowered costs aresome of the reasons why the industry adaptsmore and more automatized solutions. Furtherreasons why robots get a greater use arethe robots’ ability to handle more complextasks. The reason why robots can handlemore complex tasks is the integration ofdifferent sensors. This gives the possibility tocombine the exact movements of a robot withsensors such as cameras and force sensors.Robots are thereby able to adapt to variationsin the environment, which benefits bothsafety and increase the area of use. All theseadvantages do unfortunately come with somedisadvantages. A robot has to be programedto handle all the sensor data and refer this to apredefined trajectory. Writing the algorithmthat can handle all possible cases is both timeconsuming and hard.

A company that wants to explore these ad-vantages and investigate if it is possible to geta test setup that tests and validates fingerprint

sensors is Fingerprint Cards.

Figure 1: Fingerprint Cards’s sensor module (left) andsome of Fingerprint Cards’s sensors.

II. Methods

To get to a conclusion if it is possible to performvalidation and tests on fingerprint sensors us-ing force feedback control, an investigation ofseveral controllers and force sensors was done.The different controllers were first simulatedusing Matlab/Simulink software and then thebest controllers were tested on a real robot.Three different force sensors were evaluated:one JR3 6 DOF force sensor, one Optoforce3 DOF force sensor and one force sensor de-signed within the project that only measuredforce in one direction. The controllers weretested using an ABB IRB120 robot utilizing

1

a sensor and controller interface called ExtC-trl developed at LTH [1]. ExtCtrl is operatedthrough a graphical user interface called Op-com [1]. The robot is controlled by an ABBIRC5 controller that is running a Rapid pro-gram for the position and velocity control,when the robot is not in contact with a sur-face. When the robot’s end effector comes incontact with a surface (hopefully a fingerprintsensor) the Matlab/Simulink controller takesover and manages the force control by utilizingthe Opcom extension.

Figure 2: Figure of the complete system.

III. Results

The final setup includes a graphical user in-terface that is able to control the Rapid pro-gram, the force controller implemented in Mat-lab/Simulink and the fingerprint sensors. Thefinal controller is a discrete PID-controller. Aresult from when two pictures taken with afingerprint sensor when different forces areapplied is shown in Figure 3.

Figure 3: Pictures taken with fingerprint sensor whendifferent forces are applied.

IV. Conclusions

The purpose of this thesis was to develop andexamine a force feedback controller that couldbe used to test and validate fingerprint sen-sors. This controller should be implemented ina system that is able to: perform different testsof the fingerprint sensors and be controlledthrough a simple interface, preferably in a Win-dows environment. All these things were im-plemented and showed a satisfying result. Thefinal conclusion one can draw from this is thatas long as the force sensor is good enough, arobot using force feedback is suitable for usewhen testing fingerprint sensors, even thoughthe forces applied are very small.

References

[1] A. Blomdell, I. Dressler, K. Nilsson, andA. Robertsson. Flexible application de-velopment and high-performance motioncontrol based on external sensing and re-configuration of ABB industrial robot con-

2

trollers. In 2010 IEEE International Confer-ence on Robotics and Automation, Anchorage,Alaska, May 2010.

[2] V. Johansson. Fingerprint Sensor Test-ing Using Force Feedback Control.Master’s thesis, TFRT-6014, Dept ofAutomatic Control, Lund University,Lund, Sweden, 2016. Available athttp://www.control.lth.se/Publications.

3