Increasingly, industry is trending toward robotic handling to minimize space demands and maximize productivity. Robotic handling systems are enabling motion sequences that would otherwise require costly 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 are automated, saving labor and materials costs.
Originally developed in these automotive applications, robots and other automation technologies have made significant headway into other manufacturing sectors, including electronics, pharmaceuticals, solar energy, textiles, packaging and in material handling markets.
From Manufacturing to Handling
Precisely designed robotic solutions can fulfill material handling operational requirements for speed, torque, motion sequence, dynamics and positioning accuracy. Common designs of robotic 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, loading and unloading, case packing or palletizing and de-palletizing. In fact, many machine mechanical designs can be defined by "degrees of freedom," which can be expressed by a "custom" kinematic in current control platforms.
Depending on the design, articulated robots are capable of moving 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.
Modularity Simplifies Usage
Modular drive systems and servo controllers have paved the way for uncomplicated installation and greatly simplified wiring, with an efficient power feed to the drives via a common DC bus connection. This stands to reason since typically a robot's drives do not all accelerate concurrently. So, the regenerative energy produced in braking one motor can be fed back to the bus where it is available to other motors.
Drive systems that provide a common DC bus provide clear advantages:
• There is only one main supply to such systems, so fusing, EMC protection and safety generally are applied to a single power input for the system;
• They are more compact than systems composed of a collection of single axes servos and frequency drives.
A uniform robotic connection system should ideally be easy to handle and completely pluggable, with a minimum of on-board cabling. That requires a system with a high level of integration, real-time Ethernet communication, and an integrated drive-based safety system that is seamlessly integrated into the IPC control system without requiring proprietary hardware. A robot controller utilizing multi-core technology can make perfect use of the advantages that drive-based safety affords—elimination of the need for additional external components, a simplified system structure as the result of reduced wiring and faster stopping with a "safe stop" feature built directly into the drive.
Central Control System
Many of the advantages and efficiencies offered by automated robotic solutions were lost when the handling and robotic components of the control application had to be programmed independently. Using the performance of modern hardware platforms, robotics (including multiple robots) and machine control can be united within one central control system. To ensure that maximum freedom is not achieved at the expense of complexity, most kinematics are now added and parameterized in a control environment. It is now equally common to have the robot's path defined by a common pick position (where the product can always be found, even if moving) and a recipe defined place position. Recipes are then presented in the machine operators' terms—for example, primary product size, conveyor speed, loading and packing patterns.
Diverse machine modules can be controlled even while the coordinate transformation for multiple robots is being calculated in real time. Machine control systems on the market today are powerful enough to handle robots without needing a separate dedicated control system. The conversion of Cartesian coordinates in a robot's path of motion to the rotation of individual robot axes can be handled by high performance processors commonly found in today's automation controllers. Such integrated control architectures significantly reduce the number of needed control components. It also simplifies intra-system communication, which extends capacity, giving material handling engineers greater flexibility in design.
IEC 61131 provides the automation control of a comprehensive set of motion commands that can be used to program complex series of movements—or paths. The controller communicates motion information via an Ethernet-based field bus (like EtherCAT) with all axes in the robotic system. The dynamics and precision of the motions to be carried out can be ensured by servo motor technology. Synchronous AC servos (permanent magnet motors) are still the mainstay of most robotic applications due to their high power output and energy efficiency, but asynchronous servos (induction motors with feedback) are gaining traction within the industry because of their improved power and lower cost.
There are also various types of commissions for combining individual axis groups and creating trajectories. It doesn't matter if preset functional modules or other methods are used, the important thing is the description of the robot's trajectory—the Cartesian coordinates of the trajectory that are converted into the individual angular positions of the robot. The robot's trajectory is expressed in the form of linear, circular and point-to-point motions. More complex trajectories are approximated using sequences of individual motions (trajectory segments).
To avoid overburdening the mechanics and damaging the product being transported it is necessary to ensure that the motion, particularly between trajectory segments, is smooth and unhindered and that certain acceleration rates and speeds are not exceeded. Built-in controller software can provide functions for restricting the speed and acceleration of each axis. Auxiliary axes (like the rotary axis of a three-dimensional robot) can be easily synchronized to the planned path. The programmer can group axes, define motion and create override limits all within the programming environment regardless of mechanical function.
Software Templates Simplify Programming
Flexible PLC software templates can be used to integrate customer and application specific functions. New function modules can be created and added to templates using IEC 61131 programming language. Function modules created in this way have interfaces which allow them to be interconnected with other function modules in a simple and user-friendly fashion. The advantage is that the PLC, motion and robotic functions can be run in real time from a single controller.
Any machine function that commands a three-dimensional space, regardless of the machine appearance, can be most efficiently designed in the smallest footprint with a multi-axis robotic system. Compared to conventional approaches with separate controllers, the simpler concepts enabled by current robotic control technologies mean fewer component costs and easier engineering.
Today's multi-axis servo systems based on current industry standards offer optimal power density and help ensure efficient handling of functional packaging tasks, without the operator having to be a robotics expert. Modern robotic technologies simplify material handling system engineering and bring added values to end users—speed, performance, programming ease, longer machine life and integrated safety functions.
Robert Gradischnig is commercial manager, electromechanical products, for Lenze Americas (www.lenzeamericas.com).