Get a grip: end-of-arm tooling considerations for collaborative robots
February 11, 2019 – As many manufacturers consider transitioning to a distributed manufacturing system (DMS) for greater production flexibility, the concept of collaborative robotic implementation becomes paramount.
A power- and force-limiting (PFL) collaborative robot (cobot) with sensitive force monitoring capability is an easy-to-use machine with an industrial pedigree that is designed to work safely with, or in close proximity to, human workers without additional safeguarding. These robots lack sharp corners, exposed motors and pinch points; and, properly configured, they have the ability to work free from vision systems, laser scanners and fencing.
Although collaborative robots that are power- and force-limited are the only collaborative robots that can truly work alongside humans without additional safety hardware and process equipment, there are three other equally effective methods, as defined by ISO 10218, for collaboration and protecting workers from potentially harmful contact situations. For a robot using any of these four collaborative modes (Monitored Stop, Speed and Separation Monitoring, Power- and Force-Limiting, and Hand Guiding), end users should take care when selecting a compatible and safe gripper for their application.
From ease of programming to quick return on investment, end users have many motives for choosing collaborative automation. Regardless of these reasons, however, collaborative robots must be equipped with the appropriate end-of-arm tooling to fulfill a specific task.
The importance of end-of-arm tooling
Without the proper end-of-arm tooling (EOAT), a robot can do very little to add value to an end user’s production process. Moreover, for an application to maintain collaborative status, special attention must be given to the EOAT. While a collaborative robot itself may be safe, the entire robotic system must be considered when designing and commissioning a system that will pass a risk assessment.
For example, if a collaborative robotic arm with PFL is equipped with an end effector that features a knife or a sharp-edged tool (or even picks up a part that could cause harm), this is intrinsically “unsafe,” and the robotic cell is still dangerous to human workers. For this reason, manufacturers should always participate in a risk assessment to ensure the use of a collaborative robot does not compromise worker safety and application integrity.
Collaborative robots present unique challenges (i.e., eliminating pinch points) for end-of-arm tooling that may be unfamiliar to end users familiar with conventional robotic EOAT. A thorough risk assessment should be able to provide detailed insight for guiding companies through the following concepts to consider when choosing an end effector for a collaborative robot:
ISO safety standards
While worker safety is a primary concern with any robotic application, there are more stringent requirements for collaborative systems designed to work with, or near, human workers. Every collaborative application requires a specific type of tool that is compliant with all ISO safety standards (ISO 10218-1, ISO/TS 15066, ISO 13849-1 PLd Cat 3).
Selecting the proper end effector for a collaborative application is primarily based on an end user’s process needs, and depending on the application, EOAT can be electric, pneumatic, and, in some cases, hydraulic. Factors such as weight, speed, accuracy, complexity and power consumption should all be considered when selecting an end-of-arm tool.
Process needs and part size usually determine the type of end-of-arm tool required to meet production demands, and in most cases depending on the application, an electric or pneumatic gripper can be used. A cost/benefit analysis can help determine if a pneumatic or electric device is more advantageous over the robot system’s lifecycle.
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From simple gripper configurations such as a two-jaw parallel design or a suction cup, to complex gripper variations such as a force feedback electric gripper, there are a host of gripping solutions available to end users. While this abundance of options can be overwhelming, a good rule of thumb for decision makers to follow is to keep the technology as simple as possible.
Electric grippers offer flexibility and precision, potentially giving end users the ability to program the gripper for various jaw travel lengths. Likewise, electric grippers can provide control over velocity or force. These are ideal for applications where part size and shape may change on a regular basis. Keep in mind that electromagnetic grippers may be the best solution for parts containing ferrous materials. Typically more expensive to start with than their pneumatic counterparts, electric grippers can save on cost and complexity, especially if it allows the system to eliminate an air compressor.
Pneumatic grippers typically offer a simple open and close jaw position, compared to the programmability of electric grippers. Depending on the input air pressure provided, pneumatic grippers can adjust their grip force to varying degrees. Often designed for one product, these grippers are well suited for applications where part size and shape remain consistent. Don’t forget that pneumatically operated suction cups or magnetic grippers may also be a viable option depending on the weight and composition of your part. While less expensive upfront, pneumatic grippers can add additional cost if you don’t have easy access to compressed air.
Depending on application needs, there are end effector suppliers that specialize in certain areas of gripper technology (i.e., vacuum components and clamping systems). When choosing a gripper supplier for collaborative system, decision makers should ensure that the gripper meets or exceeds all ISO collaborative requirements.
Keep it safe and simple
Not all processes are applicable to collaborative robots, and not all end-of-arm tooling is safe to work in a collaborative manner. For this reason, a risk assessment of the overall application solution should be done to determine the potential hazards, and to ensure the proper devices are used and the appropriate risk-mitigating procedures are followed. Once this has been accomplished, end users can confidently move forward with selecting end effector technology for collaborative operation. From simple gripper configurations to complex end-of-arm variations, there is a plethora of gripping solutions available. While a large selection of electric or pneumatic options may be overwhelming to end users, a good piece of advice for decision makers to follow is to keep it safe and simple.
Sayre Jeannet is a process engineer on the technology advancement team at Yaskawa America, Inc. - Motoman Robotics Division.
This article was originally published in the Winter 2018-19 edition of Manufacturing AUTOMATION's quarterly e-book Robotics Insider.
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