PLC versus OEM robot controls

Dec. 1, 2011
As more and more manufacturing facilities and distribution centers discover the benefits of robotic material-handling solutions, the decision of how best to control the robot must be made. Here we compare PLC-based methods to OEM robot controllers.

While robot original equipment manufacturers (OEMs) each offer their own tightly integrated controllers, recent developments now enable control by a programmable logic controller, or PLC. For facilities where PLC-based controls are already used in other machine control applications, the benefits of using one for the robot as well may be a better choice than using an OEM controller, depending on the application.

Speaking robot, simplified

If you're familiar with PLCs, as many engineers are, then you already know how to read, understand, and troubleshoot a PLC-based robot. What the robot should be doing and how to do it is still required knowledge, but the hurdle of learning a proprietary OEM control language disappears, and with it much of the training time previously required.

Moving to PLC-based robotic controls brings additional advantages as well, including common programming controls, software interfaces, program backup and restore methods, and program documentation.

Robotic material handling solutions naturally include robots. In addition, these setups incorporate complex systems that include infeed and discharge conveyors, pallet dispensers, transfer cars, and other equipment. System components are typically controlled via a PLC, so that the robotic controller and system controller must interface, coordinating data and interlocks to achieve the desired functions. Depending on the complexity of the application, this interface can be quite challenging. Several robotics companies are developing control options to simplify matters, including Yaskawa's Motoman Division and KUKA Robotics.

“As we studied the packaging and palletizing markets, we recognized the need for a unified control strategy,” says Steve Barhorst, president and chief operating officer, Yaskawa America Inc., Motoman Robotics Division. “These markets have engineers and technicians with extensive experience and expertise with PLC controls and programming. We view the development of our MLX100 Robot Gateway as an easy way for these users to adopt robotics into their packaging lines without the burden of having to learn a new robot programming language. Users now gain the flexibility that robots offer in a PLC-based platform they already understand. We still offer our standard robot controller, the DX100, for applications requiring process control, like welding, dispensing, and painting.”

When the PLC that controls the robot is the same PLC that controls the other system components, it eliminates this interface point and greatly reduces overall system complexity. In addition, the controls hardware design for a PLC-based robotic controller can now utilize a common controls architecture with the system controls.

“KUKA Robotics worked with Rockwell Automation to develop the capability to control select KUKA four-axis robots to address demands from consumer packaged goods end users who were looking for a single integrated control solution for their packaging machines and robotics,” says James Cooper, KUKA Robotics Corp. “Additionally, they've requested a single point of operator interface for their automation solutions that involve traditional packaging machinery and robotics.”

In addition to shrinking the overall footprint by being housed in the same control panel, the design of the robot controls uses the same drawing nomenclature (for wire numbers and drawing numbers) as all the other hardware in the panel, thereby reducing the overall complexity of the control system design. Other benefits include simplified troubleshooting and maintenance, easier training, and common spare parts.

Flexible I/O and communication protocols

With PLC-based robotic controls, all hardware, I/O, and communications protocols available to the PLC are now also available for use with the robotic controls. This is particularly relevant when considering that large portions of proprietary OEM controller I/O communications are primarily for interfacing the robotic controller with the PLC. With this additional communication no longer required, the only interfacing necessary is to the I/O on the robot, which is as simple as any other I/O in the control system. What's more, PLC-based robotic controls support a much wider range of I/O hardware and communications protocols than OEM controllers, in order to cater to a wide variety of applications.

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Common interface, reduced maintenance

No longer is the teach pendant the primary interface with the robot controller. With PLC-based robotic controls, the HMI is now the same throughout the rest of the system. The alarm system, fault recording, data monitoring, and all other functions available to the HMI now directly interface with the robot controller. Unique faults and custom operations can be added and changed directly to the robot controller. An HMI interface allows for a much greater application-specific focus, as well as a more agile structure.

Manufacturing facilities typically integrate many different types of equipment into their operations, such as fillers, packers, palletizers, wrappers, and conveyors. There is a tendency in these facilities to favor PLC-based controls for all equipment. That's because if each manufacturer is allowed to supply its own unique control scheme, the integrated system may be functional, but a nightmare to maintain and upgrade. This is why detailed specifications exist in most manufacturing facility RFPs (request for proposals), placing boundaries on the controllers and hardware that OEMs use. A common control system makes the integrated system much easier and faster to maintain and upgrade, thereby reducing the total cost of ownership. By integrating the robot controller with the PLC-based controls system, the end user does not incur the additional costs associated with a unique control scheme.

Freedom to mix and match robots

Because the OEM controllers have their own unique language and training requirements, many companies that already have industrial robot solutions tend to prefer the facility's incumbent robot brand. This is often an obstacle to selecting the right robot model from any robot manufacturer, as many companies are unwilling or unable to support multiple robot brands because of the uniqueness of the different controllers. With the advent of PLC-based robotic controls, users are not restricted to the brand they chose for their first robot when making future purchases, as the controllers can be common across multiple brands.

PLC controls not for every application

The potential of using PLC-based controls for robots introduces a new set of decisions for robotic integrators. In some cases, PLC controls may not be the best choice. The automotive sector and other robot-intensive industries, for example, are not likely to convert from OEM controllers due to a large installed base and unique application requirements. Additionally, some robotic OEMs do not currently offer any way of provisioning a PLC-based controller.

In making your controller decision, analyze availability, functionality, and cost: In facilities where there is already a large, installed base of PLC machine control with which the robot will need to interface, the familiarity of technical staff with PLC controls over an unknown OEM controller can have a significant impact on operational and support costs. A reputable robotic integrator will ensure that the final solution provides the optimal fit, whether it is PLC or OEM based.

For more information, contact (866) 936-7300

Robot Gallery

Robotic joint modules now available
Robolink multi-axis joint modules from igus inc, East Providence, R.I., are now available for order. Robolink is designed for humanoid robots and other lightweight automation applications and includes a variety of options and components ranging from high-strength Bowden cables to drive units and attachment accessories for the robot arm. More than 100 beta testers used free prototypes to further the development of robolink for a variety of applications before mass production began. Test applications ranged from underwater, mobile, and humanoid robots to dental technology and camera guidance for production monitoring and sewage-pipe inspection.

To keep the dynamic forces of the system as low as possible, robolink's actuators and control module are decoupled from tools, such as grippers or suction cups. Cables drive the lightweight plastic joints so they can rotate and swivel freely. Space-saving drive units featuring four drive motors and one housing are also available for the joint system. For more information, contact (800) 521-2747 or

Next-generation kinematics for high-speed handling
Festo USA, Hauppauge, N.Y., will introduce a series of kinematic high-speed handling solutions over the next three years. The EXPT Tripod will be released in 2012, followed by two Cartesian configurations, the H-Gantry in 2013 (pictured) and T-Gantry in 2014. The rigid mechanical design and low moving mass make the parallel kinematic solution (delta configuration) EXPT Tripod up to three times as fast as comparable Cartesian systems. EXPT will enable up to 150 picks per minute (ppm), suitable for palletizing, sorting, and other tasks involving high speed, small parts handling. Both the H and T Gantry solutions will boost dynamic performance 30% over conventional planar surface gantries. A recirculating belt and two fixed motors enable higher acceleration due to reduced mass. In addition, both motors work synchronously together for higher acceleration forces, resulting in 60 ppm for the H-Gantry and 80 ppm for the T-Gantry. For more information, contact (800) 993-3786 or

Delta robot features direct-drive axis
Introduced at Pack Expo in September, the delta-style Motoman MPP3 robot from Yaskawa America Inc.'s Motoman Robotics Division is designed for high-speed packaging, cartoning, and kitting applications. The MPP3 robot features a three-arm configuration with a direct-drive rotary axis to simplify design and increase reliability during high-speed operation of up to 150 cycles per minute. The MPP3 is IP65-rated and features a 3 kg payload capability, a work envelope to 500 mm, and repeatability of ± 0.004 in. It is available with optional vision and conveyor tracking. The MPP3 uses Motoman's new FS100 controller, reportedly the smallest controller in its class at just 19 in. wide. For more information, contact (937) 847-6200 or

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