November 17th, 2017
This document will explore electromechanical grippers and typical collaborative robot applications that call for them. This should be of particular interest to anyone researching reliable methods to pick up and grip a delicate, fragile, or unusually shaped item.
With robotic applications expanding beyond the typical high-speed pick and place, many collaborative robot applications call for the ability to pick delicate objects that could be damaged by a pneumatic gripper or those whose shapes are not conducive to be picked by a vacuum gripper. In these situations, the electromechanical gripper can often be the solution.
Pros for Electromechanical Grippers:
- Position control
- Speed control
- Force control
- No need for air or air preparation
- Reduced cable management requirements
- Can attach customized fingers for precision picking
Cons for Electromechanical Grippers:
- Potential for higher cost
- Overall speed
- Weight and Size
- Grip Force
- Two reachable sides to grasp
Example 1: Schunk EGL/PGN
Featured Advantages: Programmable Stroke, Custom Precision Fingers, High Repeatability, Force Control.
Example Customer Case Study
The customer had solid plastic parts in a range of sizes, all on the same line. The customer was concerned with marking or scuffing the parts, as this could easily be done if a specific grip force was exceeded. There was one optimal pick location but it was blocked on either side by each part’s physical features. The pick location, as well as the entry path to get to the pick location, changed with each part size. The part had an irregular surface and no substantial flat areas with which to pick from.
Schunk EGL/PGN Specification
In this application, due to the irregular surface and no substantial flat areas, this disqualified the use of a foam/cup vacuum gripper. The parts were made of plastic, disqualifying the use of a magnetic gripper. A needle gripper could be disqualified for a number of reasons, but in this case, the specification called for no marking of the part and there was a good chance the needles would not have worked.
The most reasonable remaining gripper option was a mechanical finger gripper. A pneumatic-mechanical gripper with a padded gripping surface could have potentially worked for one or two of the sizes, but eventually, a finger changeout would be required. See the image below. Once the part sizes changed to where the empty areas, which allowed the fingers to approach the grip point, are no longer there, the original gripper finger configuration would not have worked.
Note how the grip windows expand, the fingers lose their ability to make the entry path. By the time entry path widens to the point in the picture on the far right, a finger changeout would be required to reach.
This brings us to the electromechanical gripper. The electromechanical gripper would allow for one finger set as it could be programmed to move the fingers to accommodate the entry pathway with high precision. Once in position, the force control feature could be used to apply just enough force necessary to safely pick the part and reduce the chance of marking. Schunk’s EGL or PGN-XX-E series would make good choices for this application.
Example 2: Robotiq 2F85/140
Featured Advantages: URCaps, Force Control, Long Stroke, Encapsulating Grip.
Example Customer Case Study
The customer had a series of thin-walled, aluminum pipes that had drastic changes in sizes. Due to the way the pipes were presented, the pipes could only be picked from the cylindrical face. The process would require the gripper, while holding the pipe, to go through some articulate movements for the process, and needed to be firmly held, regardless of the size. The customer was only a small, one-shop operation and was concerned about the ease of programming as they would need to be able to make changes without a programmer on staff.
Robotiq 2F85 Gripper Specification
The material was non-ferrous metal and therefore disqualified a magnetic gripper (non-ferrous) or a needle gripper (metal). There was a possibility of being able to find a foam/cup vacuum gripper that could potentially pick the aluminum pipes, but the large range of sizes and the cylindrical face convinced us to look elsewhere. A pneumatic gripper was feasible, but the large range would require a very large pneumatic gripper, along with a custom, overlapping finger setup to allow the fingers to securely grip the largest and smallest parts. Another concern with the pneumatic gripper was the force that would be applied to the thin-walled aluminum pipes.
The ideal solution for this application was an electromechanical gripper. More specifically, a Robotiq 2 Finger 140mm stroke gripper. The Robotiq’s encapsulating grip and long stroke would secure a large range of pipe diameters, without the need for custom fingers. Another feature that would help fit the customer’s situation would be the URCaps software that simplifies programming of the gripper. Simply select that you want to insert a grip move and adjust the sliders to the desired speed, position, and/or force.
Electromechanical Grippers Are Versatile But Not Universal
In conclusion, electromechanical grippers offer some of the highest levels of versatility across off-the-shelf grippers. This versatility allows electromechanical grippers to pick a wider range of parts, saving time from reduced tool change out and save money directly from reducing the number of tools needed in the solution. While the electromechanical gripper is the solution for many applications, it is not ideal for all applications. Consult Cross Company to determine what is right for your application.