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UDP
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HMI
Real-time platform
Work-piece graphical
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Environment co
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Figure 6.10: Two di
fferent configurations for the software environment featuring the WPBA
101
7 Experimental Test-rig
To invent, you need a good imagination and a pile
of junk
Thomas A. Edison
7.1 Overview
In this chapter an experimental setup implementing the work-piece based approach will be
presented. The technical realization of the first class of components [functional] in the
framework section 4.4 which included the control and software module were discussed
in chapters 5 and 6 respectively. Due to their heavy reliance on the type and characteristics
of the available hardware, the remaining two classes, [device] and [communication
architecture] will be presented here. Thus this chapter explicitly addresses the sensors
module, robot module, HMI module, task-level peripheries in section 7.2 and the
communication architecture in section 7.3. The design and development of the test-rig
is dictated by a set of requirements which takes into consideration the motivation and
objective of this work. Those requirements are listed as follows:
1. To retain the generic nature of this work and to guarantee porting of the meth-
ods introduced here to similar robotic work-cells in an industrial setting, only
commercially available and o
ff-the-shelf components are selected and used.
2. Since robot manufacturers tend to dictate the type and extent of functionalities
available to the user, it was imperative to abstract these interfaces to build control
functionalities independent from the commercial controller.
3. Maintaining the design as flexible as possible in order to simplify adding or re-
moving hardware or software and components. Regarding hardware, this meant
depending more on PC-based infrastructure to avoid being hampered by di
fferent
vendor-specific interfaces. Regarding software, most of the user interface is gen-
erated in run-time hence it is not hard-coded. Furthermore, those interfaces are
subsequently saved in configuration files to avoid repetitive initialization sequences.
4. To prevent hogging of the communication bandwidth and to avoid choking of data
at critical locations, dedicated hardware and compact e
fficient data representation is
utilized.
7 Experimental Test-rig
Although those requirements dictated certain design decisions, they nevertheless allowed
a continuous improvement of the overlapping aspects of the test-rig. Thus the test-rig was
being continuously improved in terms of hardware and communication in order to retain
the design concept represented by the requirements.
7.2 Device components
7.2.1 Robot platform
The robotic platform consists of two KR6
/2 industrial class robots from KUKA connected
to a KRC2 industrial controller from the same manufacturer as shown in Figure 7.1 (KUKA
GmbH 2011a)(KUKA GmbH 2011b). Although weighing about 250 Kg each, they have a
payload of 6 Kg at a maximum TCP velocity of 2 m
/sec, hence their application is limited
to pick and place small components or non-contact tasks. The robots are mounted on thin
steel plates which in turn are mounted on a custom-made aluminum structure. To avoid
any unwarranted vibration during motion, the steel plates are diagonally reinforced from
underneath. One of the major advantages of such a structure, is eliminating the need for
re-calibration of the whole test-rig during transport. Mechanical stoppage are mounted
on the first and second axes of the robots on both sides limit the motors’ motion. This is
supplemented by software limit switches to decrease their workspace.
7.2.2 Sensors
For force sensing and monitoring, two FTS supplied from SCHUNK are utilized. They
are designated as FTC-50-80, where FTC stands for Force-Torque-Compliant (Schunk
2011). They are capable of measuring the forces and torques in 3 translational and 3
rotational DOF. Their compliant nature comes from their internal design, where springs
are used to measure the loading while elastically deforming (up to 1.0 mm and 1.4
0
in all
translational and rotational directions respectively). Thus they are adequate for executing
constrained tasks such as assembly. For convenience, the sensors are mounted such that
their coordinate system corresponds to the coordinate system of the robots’ TCP. Therefore,
simplifying the conversion from one coordinate system to the other. The maximum force
that could be measured in all directions is around 300 N. On the other hand the maximum
torques in the lateral directions is 7 Nm, and in the perpendicular direction is 15 Nm.
An internal controller converts the analogue signal to a digital one and sends it over a
CAN-bus
1
with a Baud rate of up to 1 MBaud.
1
Controller Area Network according to the ISO 11898:2003 standard
104
7.2 Device components
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