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Cobots, traditional robots, or something in between, how to choose the right robot for you

David Miller

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With the introduction of cobots (collaborative robots) into the manufacturing environment, many people struggle to understand the limits of cobots and rush to assume that every new application they see is a good fit for a cobot.  There are several factors to look at when deciding between a cobot, a traditional robot, or a traditional robot with integrated safety components for an application. 

  • Amount of human interaction
  • Proximity of human traffic
  • Process positioning tolerances
  • Part cycle times
  • Complexity of integration 

 Amount of human interaction:

You should examine how often people step into the robot work area to do things such as adding raw materials or removing finished products frequently.  If this interaction frequency is high to moderate, the best solution will lean towards a cobot or a highly safeguarded industrial robot. If this interaction is low or non-existent, any one of these solutions fit.

 

Proximity of human traffic:

Determine if other workers will be moving or working in very close proximity to the robot (within physical reach).  If people are within reach of the robot, such as working side-by-side handling products coming down a conveyor line, the robot must be a cobot.  This is one of the leading applications for implementing cobots.  Due to their flexibility and ease of programming, they can be re-deployed to fill in for a worker shortage or add resources to the line during peak operational times.

If human traffic is rare or only occurs in one particular area within reach of the robot, a safety guarded traditional robot may be the best choice and will have the benefit of higher speeds.

 

Process positioning tolerances:

Does your application need a robot that repeatedly goes to the same position within tenths of millimeters or does it need to be within twenty microns or less?

Most cobots on the market have a positioning repeatability of +/- 0.1mm.  This repeatability is sufficient in most applications where you teach a robot to perform a human-like function.  If your application requires a higher degree of repeatability, you have two options.  1) Use a cobot along with mechanical aids to achieve better results.  2) Use a traditional robot which averages +/- 0.02mm and can achieve +/- 0.010mm on some models.

 

Part cycle time:

In many applications this one factor can drive the decision one direction or the other.  Since cobots cannot move faster than the safety rating of 250mm/sec, the cycle times of your pick and place type processes can often take 3-5 seconds depending on grasping times and release times.  Traditional robots have a typical pick and place cycle time of 1-1.5 seconds.  This is one of the biggest differentiators between the two robot types.  If the number of parts to be processed per minute is low, a cobot may be a good fit.  If the parts per minute requirement gets up over 10PPM, you have two choices.  1) Use a cobot to perform a multi-part pick/process on accumulated parts. 2) Use a traditional robot for its high-speed capabilities.

 

Complexity of integration:

Integration complexity can range from a simple teach by demonstration pick-and-place program to creating a PC-based upper-level language application to control the robot using direct execution commands. Interaction with other third-party devices can also add to the complexity of integration.

If your application is a simple pick and place of a fixtured part, then a cobot is an excellent choice since the complexity in programming is much less and could be classified by some as “fun”!  Most cobots have the means to teach by demonstration.  This means that the user manually moves the arm to positions and presses a teach button to memorize the locations.  Even if your application includes vision to pick or place the part, a cobot may still be the best choice since some cobots do a fantastic job of seamlessly adding vision to an application without all the steps of setting up a camera system separately.

 Suppose your application requires utilization of factory protocols to control the robot, integration of a PLC or PC, or integrating third-party components into the system. In this case, a cobot may still be a choice, but the level of programming complexity increases dramatically.  In most applications with this high level of sophistication, a traditional robot with all its existing infrastructure to complete the integration would be the best choice

 

In Summary:

Cobots are a great fit to applications that require a medium to high amount of human interaction, as long as the system’s slower speed is acceptable.

Industrial robots are a great fit for applications that require high precision or high speed ( > 250mm/sec).

Safety guarded industrial robots are a great middle of the road fit where high speed and precision is needed but the robot must still work near or interact with people occasionally.



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This is a great examination of robot types, Dave. I like your point regarding achieving positioning tolerances with a cobot by using a mechanical aid.

This illustrates the need for flexibility in the robot selection process. There may be combinations of technology that can push through design constraints.  Some of the advancements we've seen recently on the collaborative robotics market are good examples:  Kassow's 7th Axis which can access difficult and intricate reach combinations that would normally require complex mounting; Mitsubishi's collaborative robot , the RV-5AS-D, which has a more traditional Industrial construction and the new MR-J5 Servos on each joint that utilize advanced vibration suppression, which enable this Cobot to have a pose repeatability of  +/- .03 mm. 

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