Unified Components and Controls for Robot Kinematics

May 31, 2011

5 Min Read
Unified Components and Controls for Robot Kinematics

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.

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

Sign up for the Design News Daily newsletter.

You May Also Like