Don’t you wish your machines would just run themselves!?
Some machines do! Many new machines are being sold with fully automated material handling solutions. The machine does the specialized task it was designed to do (such as turning) and handles the material in and out of the machine….
But like cars on the road, not all machines are new. In fact, most manufacturers have fairly dated equipment that is still chugging along extremely reliably. Especially small to medium enterprises (SME’s).
Most of these machines were designed with humans in mind… Meaning that they were meant to have human operators….
Who perform a wide variety of important tasks:
- Identifying and organizing unfinished and finished parts
- Handling raw materials into the machine
- Work holding actuation
- Actuating safety barriers
- Initiating the program, “pressing the big green button”
- Handling finished parts out of the machine
- Cleaning work holding
- Post processing
- and Quality control checks
Basic Principles of Designing an Automated Work Cell
So if we want to effectively automate a production process, we are talking about a lot more than just material handling.
The automated work cell has to be designed so that most of the tasks that the operator previously did can be accomplished with a robot and other supporting equipment. We can come up with an effective work cell design by adhering to a few basic principles.
- Decrease the Cycle Time for Primary Equipment
If the piece of equipment is expensive, expensive to run, or a bottleneck for the process, we want to time other tasks to the cycle time of the primary piece of equipment.
- Optimize the Layout
We want to optimize the layout of the work cell to minimize travel distances and to ensure the robot can reach all pieces of equipment.
- Optimize Motion
Speeding up and shortening movement can help reduce cycle time. Slow movement is still necessary in some parts of the motion for accuracy and consistency, especially in the prehension or gripping stages of the motion.
- Fixture Everything
A robot is like you trying to find the light switch in the middle of the night. The robot can’t see anything but it knows where things… if they don’t move around. It’s really important that the robot does NOT move with respect to the machines and that fixtures don’t move with respect to the robot.
- Routine Inspections
Even though you may have automated a process, skilled staff are still required to routinely inspect the work cell. There should also be a maintenance program where certain aspects of the work cell – especially wear components are checked, replaced, or re-calibrated after a number of cycles.
Methods for Organizing Finished Parts and Raw Stock
Let’s have a look at each “task” that is part of machine tending and see how we can automate it.
A machine operator organizes the unfinished stock and finished parts out of the machine.
Typically an operator might stack finished parts in a cart.
Robots need to be a bit more regimented about how parts are organized. This can be accomplished with many aids:
- Feeders, Ramps, Magazines
The robot grabs the raw stock, places it in the machine, and the remaining stock moves down into place – ready for the next part. - Conveyors
Shows the use of conveyors to transport finished parts - Cartridges and Trays
- Here is how cartridges and trays can be used to hold parts pre and post machining.
- Trays are often arranged in an upright position. This uses gravity to ensure the parts locate themselves in the right position in the tray.
- Typically you would teach the robot where the uppermost left corner of the grid is and the lower most right corner, tell it some details about the spacing and how many parts there are, and then the robot can easily find all the parts.
- In some instances you can stack the parts in a bin when the part geometry lends itself well to stacking and you aren’t too worried about the part surface finish
- Stacking / Palletizing
- Similar to how robots can be taught how to grab raw stock from a tray, they can be taught how to palletize and arrange parts in a grid.
- This clip even shows how the program grabs a divider so that it can palletize multiple layers of finished product.
- Bin Picking
- Picking parts out of a bin is relatively easy for a person but requires sophisticated vision software to be able to do with a robot. There are plenty of solutions for this now as you can see here.
- There are many different methods, some use special lighting and cameras, while others use laser scanning.
- One of the main challenges that these technologies solve is identifying which parts are located on the top of the pile and figuring out how to grasp them.
- Ultimately the main benefit is that if you have a large number of parts, they don’t need to be organized by people into nice trays in order for your work cell to begin working.
- Vibrator Tables to Orient
- On occasion, a vibrating table can be helpful to reorient parts for picking if they do not present themselves in an ideal orientation.
- I’ve see some solutions that bypass fancy laser scanning of the pile by just grabbing a handful of parts, and placing it on a vibrating table with a light and camera…
- Classical vision technology is very good at recognizing parts when there is only a single layer of parts and the grasp orientation and location of the part can be determined very easily this way as well.
- Cameras and Barcode Readers
- It is not uncommon to integrate cameras and barcode readers into automated work cells these days.
- These are used for part identification and can read barcodes, to data matrix, QR code, or even a dot peen
- Part identification is very important for quality control
- In modern manufacturing where consumers are demanding higher amount of customization…
- or for manufacturers that need to adapt quickly to different types of parts…
- it is important because the part identification can also drive what program is loaded into the machine.
- In other words, with some limitations, you can do mass manufacturing of custom parts with the same automated work cell.
Final Remarks
It’s pretty easy to get carried away with automation. At some point you do need human intervention for maintenance, inspections, and to reload the cartridges or carts.
Of course, all of these things can be automated as well… but its important to determine which tasks have real ROI and automatable value.
End Effectors
The choice of end effector is an important decision for quality and cycle time optimization.
- Multi ended end effectors allow for multiple part handling so finished parts and blanks can be loaded and unloaded at the same time. When the end effector can complete several processes it saves on motion, trips, and tool changes.
- Many end effectors also incorporate pneumatic nozzles to help with cleaning the fixtures.
- Force perception may also important so that soft objects are not squished or to prevent marring of softer metals.
- In most cases, custom jaws for gripping end effectors typically help maintain more secure part holds and also more accurate placement.
- For certain applications, vacuum gripping and magnetic gripping may be appropriate.
- Multiple specialized ma chines or multiple end effectors may help sync the timing of post processing tasks with the primary process.
Work Holding
Typically when parts are placed in a vise by an operator, a torque wrench is used to tighten the vise. This ensures a consistent clamping pressure which is one factor in part consistency.
In machine tending the most common solutions are pneumatic such as:
- Air Powered Motor Vise
- Pneumatic Vise
- Retrofit Pneumatic Vise Actuators
- Although there are hydraulic vise solutions out there…
- Hydraulic Vise
The main goal with all of these solutions is to provide automated vise opening and closing, as well as consistent and reliable clamping pressure.
It’s much easier to actuate a pneumatic vise then to try to get a robot to turn the handle on a torque wrench.
Intermediary Fixtures
Sometimes an intermediary fixture is required when the robot needs to change its grip on the part during the process.
Verification and Quality Control
It is also possible to incorporate de-burring, polishing, sanding, washing, and other post processing tasks. Quality control can also be part of the automated work flow.
One Added Benefit…
To an automated work cell is that several tasks can be executed simultaneously. For example, the door to the machine can be opened at the same time as the robot arm grabs a very heavy object.
Personally, I prefer to see the machines of the work cell closely integrated together so this can happen. It seems silly when a robot has to open the door to the machine for example and press the big green button.
Combining your robot with gantry movement can also vastly increase the robot’s reach and maximize the value of your investment. The gantry movement is shown here, but it is possible to use this to have a single robot manage multiple work cells with long cycle times.
Thank you!
I hope this has given you some insight into what goes into an automated work cell and machine tending applications.
If you’d like to check out my last video breaking down Food Prep Automation and how it is helping restaurants reduce real estate costs, check it out in the link down below.
Please share the video with a friend!
Thanks again for watching.
I’m Stephen Bruce Wong with Automation Experts, and I’ll see you in the next one.
