The process of selecting/designing a robotic end effector can be overwhelming due to the various design factors. There are so many options out there and how do you know when to customize an existing end effector vs. a full-custom build?! I use the following table to help organize my design and ensure that all the applicable factors have been addressed. This process also allows me to tackle one item at a time instead of rushing into it and getting stuck half-way through.
For your convenience, I have high-lighted my top 15 considerations.
| Category | Design Factor | Clarification / Example | |
| Part Characteristics | Weight | Mass of the object, which could change due to a machining process. | |
| Size | Any internal and external dimensions that may be in contact with the gripper or possibly interfere with the robot arm movement. | ||
| Surface Protection | Soft materials and high polish surfaces may be susceptible to scratches or scuffing. | ||
| Shape | The part is asymmetrical, spherical, angular, or has drilled holes or channels. | ||
| Tolerance Variability | Parts within a batch could vary in size or weight. | ||
| Part Stability | Soft and thin parts may deform easily when gripped or moved. Top-heavy parts may need added support to avoid tipping. | ||
| Surface Cleanliness | Part or finger surface may have oil, dirt, dust, chemicals, or residue, which could affect the gripping ability of the end effector. | ||
| Gripping Method | Mechanical Pinch | Pinching action caused by actuating fingers, which can contact internal or external features of the part. | |
| Scoop | Scooping action that cradles the part like a forklift. | ||
| Vacuum Cup | Vacuum Cup or plate that uses vacuum pressure to lift an object. | ||
| Magnet | Electro-magnetic force that can pick up metallic objects. | ||
| Balloon | Rubber Balloon that inflates around or inside the object. Very useful for odd-shapes and variable sizes. | ||
| Process – Other | A grinding wheel, paint sprayer, or drill that is installed on the robot arm and performs a task without actually gripping the part. | ||
| Power Transmission | Pneumatic | Uses air or gas as the working fluid. | |
| Hydraulic | Uses oil or similar liquid as the working fluid. | ||
| Electrical | A motor or magnetic coil that uses electro-magnetic force to rotate a pivot or slide. | ||
| Mechanical | Springs, rubber bands, or flexed materials that uses deflection force. | ||
| Gripping Force | Weight of the Object | The end effector can withstand the static load of the part, as well as the process momentum of the part. | |
| Method of Holding | Refer to “Gripping Method”. | ||
| Finger Friction | Friction needed to keep the part from slipping out the fingers. Cleanliness may be a factor as well, see “Part Characteristics – Surface Cleanliness”. | ||
| Process Speed and Acceleration | High speed and acceleration will result in high momentum forces on the gripper, possible causing the part to fly out. | ||
| Part Positioning | Length of Fingers or Cups | Longer fingers will allow for deeper access, but also requires clearance above the part for retraction. | |
| Robot Accuracy | Low accuracy robots may need external guides or fixtures to achieve repeatable actions. | ||
| Upstream Variability | Part location of the part may vary. Possible solutions would be a vision system or bowl feeder. | ||
| Downstream Tolerance | High-precision processes after the robot may require very high-precision placement. | ||
| Access Restrictions | Confined areas may not allow for large end effectors, such as a CNC machine or assembly line. | ||
| Gripper Service | Lifetime of Components | Rubber fingers may wear out. Plastic may become brittle due to UV radiation or chemicals. | |
| Removal of Components | Suction cups or rubber fingers are easily removable. End Effector design has bolts or quick-turn knobs instead of glue or welds. | ||
| Availability of Parts | Suction cup sizes are standard and materials are easily obtainable or widely sold. | ||
| Operating Environment | Temperature | Low and high temperatures may affect the end effector’s strength, causing premature failure. | |
| Humidity, Water spray | Especially prevalent with electronics, you may need to source IP rated components Water spray protection is the second number of an IP rating (IP45). | ||
| Dirt, Dust | Ingress of dirt and dust may cause electrical shorts or excessive heat, so you may need to source IP rated components. Dust protection is the first number of an IP rating (IP45). | ||
| Safety | The robot area may be situated in a high-traffic area, which would require certain safety protocols. See “Safety” for more details. | ||
| Temperature Protection | Heat Shields | Incorporate foil or temperature blankets that reflect heat away from critical components. | |
| Long Fingers | By extending the heat source away from the end effector, less heat will reach the gripper body. | ||
| Forced Cooling | Air or liquid can be used to accelerate the cooling process. | ||
| Heat-resistant Materials | The gripping material can withstand direct contact with high heat, such as silicon. | ||
| Gripper Materials | Strength, Rigidity | Longer fingers may require added structure to prevent flexing. | |
| Fatigue Protection | Highly repetitive actions can cause material failure even though the payload is low. | ||
| Cost and Availability of Components | Titanium is a lightweight and strong material, but extremely expensive compared to aluminum. | ||
| Gripping Friction | Rubber materials offer great friction force, but only for certain materials and environments. | ||
| Chemical Compatibility | Parts that are contaminated with acids or chemicals may require special handling. Even water and oil can degrade certain materials. | ||
| Safety | Sharp Edges | End effector has sharp edges or corners that could cut wires or people, especially for high-interaction automation such as collaborative robots. | |
| Gripping Force | Finger actuation could crush a human hand and may require a lower gripping force. | ||
| Pinch Points | Pivoting joints can pinch wires or tubing, which can be guarded with plastic or fabric. | ||
| Collaborative Design | In general, all corners and pinch points are guarded or padded and gripping force is limited to the minimum value to grip the part. | ||
| Sensors | Area scanners around the robot can disable the end effector. Force sensors in the fingers could detect an unidentified object, limiting the gripper power. | ||
| Mounting Requirements | Robot Bolt Pattern | The bolt pattern on the robot wrist may require a custom mount, especially for custom end effectors. | |
| Robot Strength | The wrist bolt pattern and arm can physically handle the payload and forces of the end effector. | ||
| End Effector Control and Power | The end effector may require air, electric power, or control connections. Some Robot arms already have I/O connections at the wrist for easy installation of end effectors. | ||
| End Effector Profile | The overall profile of the end effector won’t interfere with the arm joints. A 2ft long end effector or part may hit the robot arm, causing major damage. | ||
| Other | Quick-disconnect Tool Change | Non-tool disconnection such as pull pins, quarter turn knobs, or air-brake couplers can limit the amount of time needed for tool-changes. In some cases, the robot can self-change the gripper and continue the process. | |
| Interchangeable Fingers | The fingers can be swapped out for various part profiles. You will want to utilize easy-to-remove fingers, as noted in “Gripper Service – Removal of Components”. | ||
| Color | It may seem trivial, but having a similar color to the robot will make your design look professional and seamless. | ||
| Design for Breakage | The motor cam or fingers would break before damaging the part, especially for highly delicate or expensive applications. You could also integrate compliant fingers that would flex in the event of a collision. | ||
| Multi-function | Dual-grip end effectors can offer higher cycle rates compared to a single grip, due to the reduced arm movement. Dual-grip designs can also offer multi-size picking, which would otherwise require a tool-change. | ||
| Fully Custom or Customize | In some cases, it’s cheaper and easier to customize an existing end effector platform instead of designing a fully custom gripper. For example, you can 3D print some custom fingers and install them on an off-the-shelf gripper. | ||
It’s easy as an engineer to overcomplicate the design, so my best recommendation is to list the critical functions and work out from there. By listing the design requirements, it’s easier to prioritize one feature over another. This also helps motivate yourself to finish one problem before moving on to the next.
If you have any questions about the information above, need assistance with a robotic application, or have suggestions to add to the list, I would be glad to discuss it with you!