IEEE Robotics & Automation Magazine - December 2015 - 104

arithmetic and logic instructions between motion commands
while the robot is moving, i.e., processing them during the advance run (the instructions run in advance of the motion).
Using the system variable $ADVANCE, it is possible to define
the maximum number of motion blocks that the advance run
can process ahead of the main run (the motion block currently
being executed). Since the main loop of the server program consists of only one instruction, the system variable $ADVANCE is
initially set to one to avoid the unwanted execution of the same
line of code. Inside the main loop, a relative movement is iteratively executed to the global variable MYPOS, which is the one
that stores the target position. The key word C_PTP is used to
approximate the movement. The approximate positioning instruction is executed in a time-optimized manner: there is always at least one axis moving with the programmed acceleration
or velocity limits. The system simultaneously ensures that the
permissible gear and motor torques for each axis are not exceeded. Furthermore, the higher motion profile, set by default, ensures motion that is optimized in terms of velocity and
acceleration.
Case Study 2
In this case study, JOpenShowVar is adopted to perform a
2-D line-following task with the same Kuka robot used in the
previous example. In this case, an open-loop off-line application is implemented using the standard kinematics provided
with the KRC. The considered task can be used for applications such as advanced welding operations. In this experiment, a camera is mounted on the robot's end-effector and
can capture a photo of the desired line to be followed on a

Camera

plane. This vision feedback is used for the off-line detection of
the path before starting the movement. In particular, once a
photo of the line to be followed is taken, the operator manually selects the desired initial and final points. Then, the A )
search algorithm [12] is used to efficiently find a traversable
path between these two points within the region covered by
the desired line. The detected traversable path is sampled with
a predefined resolution and the resulting samples are stored in
an array variable. The same array is used as an offline input
for the robot's end-effector to be actuated point by point. The
experiment setup is shown in Figure 7.
Case Study 3
In this case study, JOpenShowVar is used to control the same
robot (from the previous case studies) in a closed-loop and with
a custom control algorithm. This is done to highlight the potential of the presented interface in developing alternative control
methods that do not use the standard kinematic model provided by Kuka. Moreover, a Leap Motion controller [9], shown in
Figure 8, is used as an alternative input device to control the
robot. The Leap Motion controller is a small universal serial bus
(USB) input device that supports hand and finger motions as
input without requiring contact or touching. This controller is
designed to be placed on a physical desktop, facing upward.
Using two monochromatic infrared (IR) cameras and three IR
light-emitting diodes (LEDs), the device observes a roughly
hemispherical area, to a distance of about 1 m. The LEDs generate a three-dimensional pattern of dots of IR light and the cameras generate almost 300 frames/s of reflected data, which is
then sent through a USB cable to the host computer. Next, it is
analyzed by the Leap Motion controller software and can be retrieved using the Leap Motion APIs. While the Leap Motion
controller makes it possible to control all of the joints in human
hands, in this specific case study, only the DOF of the wrist are
used as an input signal to control the robot's end-effector. Each
DOF of the wrist corresponds to a translational axis in the workspace of the robot to be controlled. When operating in position
control mode, the input device works as a position proportional
replica, so that the wrist motion maps exactly to the motion of
the robot's end-effector with constant speed, while, when

Arbitrary Line to Be
Followed

Reference
Points

Figure 7. Case study 2: the experiment setup for a 2-D linefollowing task with the Kuka KR 6 R900 SIXX manipulator. (Photo
courtesy of KUKA Robotics Corporation.)

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IEEE ROBOTICS & AUTOMATION MAGAZINE

DECEMBER 2015

Figure 8. Case study 3: the Leap Motion controller used to
operate the Kuka KR 6 R900 SIXX manipulator. (Photo courtesy
of KUKA Robotics Corporation and Leap Motion Inc.)

Table of Contents for the Digital Edition of IEEE Robotics & Automation Magazine - December 2015