Q&As When Developing a Robotic Manipulation Cell (Part 2/2)
Posted on Jul 02, 2015 12:08 PM. 6 min read time
In a recently posted article we explored a list of Q&As designed to help people who are in the process of automating manipulation tasks. These Q&As are mainly targeting the parts themselves, as well as some aspects of the company that should be considered. You will find below some more Q&As, this time more directed at the process and the robotic cell's surroundings.
As in the previous article, we considered an example application where some parts have to be picked from a conveyor belt, passed in front of a camera for a quality check and dropped inside boxes. In this article we will use varying scenarios.
1. What is the desired cycle time for the task?
This is often one of the most important aspects of the project as it is directly relates to payback. By splitting cycle times into smaller segments, this will help you find the proper components for each step of the application. For the example described in the introduction, you could breakdown cycle times as follows:
- Time for the robot to get to the position above the part to be picked.
- Time for the robot to move to the camera position.
- Time for the camera to analyze the part and provide pass/fail status.
- Time for the gripper to close on the part.
- Time for the robot to move to the dropping position.
- Time for the gripper to release the part.
- Time for the robot to return to its initial position (to complete the cycle).
Breaking out the cycle time in this manner allows you to see the impact of the various components/processes on cycle time. Therefore, as you work out your solution, it will be easier to target time consuming tasks and optimize them separately in order to meet your overall cycle time objective.
2. Which segments of the robot's motion need to be more accurate than others?
First start by splitting the motion of the robot into different segments. Most robots offer different point termination settings. For example, you may have a FINE termination setting which makes the robot stop exactly at the required position. You could also have a CONTINUOUS termination setting at points on the path segment where the robot simply needs to pass close to the requested points but not exactly at the points. In this case, the robot’s motion does not stop and therefore you will see a more fluid robot motion. Sometimes you can even adjust a parameter for the continuous termination setting to tell the robot how close you want it to move to this point. So you can adjust these features to get either a less accurate, but more fluid robot motion or a more accurate and slower motion. Generally it is a good idea to keep things simple at first and once everything is up and running then you can start fine tuning the application by changing point termination settings.
3. How accurate do you have to be to pick the part?
This really depends on what you have to do with the part once it has been picked up. If you have to load a lathe for example, it is nice to have a tool where the part self-centers when it is being picked up. On the other hand, if you simply need to pick the part and drop it randomly inside a box, then there is no need to have constant positioning of the part.
4. How are the parts presented to the robot?
The main thing is basically figuring out if the parts are presented to the robot in a repetitive manner so that you can predefine picking positions in the robot program. Otherwise, you may need to locate the parts before picking. For example, if the parts arrive from a conveyor, you may want to link the conveyor’s encoder output to the robot and include a vision system to make sure you are able to pick the part when it gets to the picking region on the conveyor. Again the picking precision required and the part’s size and shape will define the specifications for your vision system when applicable.
Be careful, vision systems have become cheaper and simpler as the technology has evolved. Therefore, the costs of designing and manufacturing jigs to consistently present parts to the robot may outweigh the cost of a simple vision system that could be used to replace these jigs.
The surroundings and layout1. Is there any equipment surrounding the robot that needs to communicate with the robot?
Sometimes, the robot itself is not the only component in a manipulation cell. The robot may need to communicate with conveyors, sensors, safety devices or sometime even your Enterprise Resource Planning or ERP system. Make sure you accurately draw the appropriate production sequence prior to designing and programming your robotic cell. Take some time to figure out in detail the impact of the surrounding components on this production sequence. Spending some time on these details in the beginning will avoid surprises later when you will be integrating the workcell into your production line.
2. Do you have access to a pneumatic line?
Before working on component selection, check whether a pneumatic line is accessible or not. If it is, make sure to characterize this line so you can search for components that fit on this line without the need of modifications. If a pneumatic line is not available, focus your research on electrical components. With prices of electrical components going down as technology evolves, take some time to calculate the difference in operating costs for a pneumatic component versus an electrical one. You may be surprised by the results.
3. How can you minimize floor space for the robotic cell?
Once you have worked out some ideas for the project, check on how you could make the robotic cell as compact as possible. Here is a list of advantages showing the importance of this point;
- You will reduce the work envelope of the robot. Therefore, maybe allowing you to select a smaller and cheaper robot.
- You will reduce robot motions between path points, thereby saving on cycle time.
- The robotic cell will take less floor space therefore allowing you to use this unused space for something else.
- It is often easier to make a small cell safe then larger ones. For example, you may be able to lock the cell inside a small booth instead of having safety fences all over the place.
4. How should you mount the robot (floor, wall, roof)?
The best way to answer this question is usually through a robot simulation software which will test the different positions for the robot. Trying the different options for robot positioning may allow you to use a more compact cell.
5. How can you integrate the electrical panel and robot controller into the design?
To make this robotic cell as compact as possible, try to look for unused space in your design where you can include the electric panel/components and the robot controller. Keep in mind that these have to be accessible for maintenance purposes.
Hopefully the above Q&As along with the ones listed in the first article will serve you well when trying to develop a robotic manipulation cell. Again paying attention to details early in the process will save you some time down the road and will reduce the risk of running into unplanned obstacles. For another example and further information you can read the free ebook on machine tending below or visit our resource center.
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