Robots and handling
systems are critical components for factory automation, enabling motion
sequences that would otherwise require extensive manual labor, such as
automatic equipment assembly, loading and unloading, picking and palletizing.
In modern automotive factories, up to 95 percent of "body-in-white" processes -
where a car takes shape - are automated, thereby saving labor and materials
costs. In a typical welding application, for example, a robot might place 30
welding spots every 60 seconds, thus achieving short cycle times and an
extremely high level of repeat accuracy.
Drive selection depends on the application,
mass to be moved and the dynamic performance required. Elements used for the
connection of the drives and mechanical components typically include shafts,
spindles and toothed belts. Gearboxes are sometimes connected directly with the
mechanical joints.
Common designs of robots and handling systems include articulated
robots, parallel kinematics systems, gantry systems and linear axis systems.
For example, a 6-axis vertical articulated robot has six degrees of freedom and
can therefore be used universally for mounting and handling of product parts in
the automotive and plastics industries.
Other robot types, such as gantry robots, are commonly used in
larger working areas for bigger machines or palletizing and de-palletizing.
Depending on the design, articulated robots can move a range of load sizes with
a repeat accuracy in the range of one-tenth of a millimeter. A central robot
controller coordinates control of the servo inverters, which together with
servo motors or geared servo motors, enable dynamic and precise motion
sequences.
Integrating Robots into
Machinery Control
Factory
and building automation for manufacturing was a strong draw at the April 2011
Hannover Messe industrial trade fair in Germany. Highlights included a
completely
automated pick-and-place application. In this application,
incoming and outgoing conveyor belts run in parallel at the center of the Lenze
demonstration rig. A Delta robot is installed at one end, and a SCARA (selective compliant
articulated robot arm) robot at the other end.
The incoming conveyor belt transports unsorted colored discs. The
material is then picked quickly and accurately by the Delta robot and placed in
predefined patterns at the desired location on the outgoing conveyor. The
deposit pattern is sorted by the SCARA robot. When the pattern is completely
filled, the Delta robot runs a standard deposit cycle or robot path with the
corresponding pick-and-place velocity, rotating and transferring pieces from
belt two to belt one in a mirror image of the original. Simultaneously, the
SCARA robot begins filling the next deposit pattern.
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A range of products and systems are available to handle this
complex task. The core control element in this demonstration was the L-Force
Controls 3200 C, which was designed to handle process and motion control
applications. The L-Force coordinates the Delta and the SCARA in real time and
in parallel, converting the Cartesian coordinates of the trajectories into the
angular positions of the robots' individual motion axes. The integrated control
architecture significantly reduces the number of required components and
simplifies intra-
system communication.
The I/O system attaches directly to the
controller via a common, fast backplane bus communicating with the six movement
axes of the robots - all multi-axis servo inverters with integrated safety
functions. Servo motors provide the dynamics and precision required in the
execution of movements in combination with absolute value encoders for the
delta robot and resolvers for the SCARA robot. Two 8400 HighLine Inverter
Drives connected to the controller via EtherCAT supply the asynchronous motors
for the conveyor belts. All drives on the demonstration rig rely on the same dc
bus, thereby requiring just one power supply unit or one brake chopper.
In this system the controller acts as a
hardware platform for the process and the motion control. The L-Force
I/O-System 1000 modules are integrated through a shared fast backplane bus.
Multiple 8400 drive packages are in operation. These are compact drives
comprising an inverter, 3-phase ac motor and gearbox.
The demonstration system was equipped with two visualization
devices (Command Station CS 5050 DVI and Command Station CS 5700 with Ethernet
interface) operating the machine modules. A CPC 5100 communicating with the
visualization and command stations of the machine via Ethernet functioned as
the hardware platform for visualization and the camera evaluation involved in
parts detection. The visualization application was created using the VisiWinNET
integrated development environment.
Shortage of space is the rule in virtually every production
facility. It is a condition exacerbated by the increasing complexity of modern
manufacturing cells. In comparison to earlier iterations, the latest control
cabinets are immediately appealing for considerably more compact dimensions.
For example, the modular and compact KUKA Power Pack integrates a power supply
module and up to two servo controllers as a standard offering. The KUKA Servo
Pack combines three servo controllers in one unit with peak currents of up to
64A per axis. A control cabinet holding up to three units next to each other
could potentially power eight axes with controlled precision. Use of modular
control cabinets greatly simplifies installation and wiring.
A power feed to robotic drives, implemented through a dc bus
connection, lends energy efficiency. A robot's drives normally do not all
accelerate concurrently. So, the regenerative energy produced in braking
operations is fed back to the bus. Because of the consistent modularization,
particularly where external dimensions are concerned, the KPP power supply,
with or without axes, and the KSP servo pack with three axes, reduce storage
space and have the same standard compact footprint.
Common and open industrial standards, such as MultiCore and
Ethernet are replacing limiting, proprietary hardware solutions. And, many
functions have been transferred to the control and drive software. All of this
opens the way for new performance and development possibilities. So that
maximum freedom is not achieved at the expense of complexity, parameter setting
in a servo system should take place entirely in the background. The servo's
entire range of functions - synchronized set points and actual values, adapting
process and diagnostic data to the integrated oscilloscope function, or a safe
stop - remain available through a standard Ethernet-based communication
interface.
Marvin Tisdale is manager - Automotive & Mobile Solutions,
Lenze Americas
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