Global Perspective: Robotic suction cup analysis

Deformation analysis optimized use of suction cups under combined load for robotic product handling with vacuum gripping heads.

07/08/2011


Loading of suction cups during the handling or motion (chassis of service robots) cycle is highly variable. Specific cases of suction cup load (loading in the radial and axial direction as well as the torque and heeling/tilting moment loading) can be monitored and analyzed. Specifically defined boundary conditions and a material model of contacting bodies can improve deformation behavior and robotic efficiency. The simulation finds admissible margin for a variable (contact stability, for example) of the suction cup deformation depending on the margin allowed for safety.

Set a safe margin

Robot handling of certain products typically uses vacuum gripping heads. During application setup, it is necessary to specify the suction cup safety level so that the gripping or holding system satisfies stability requirements, accounting for possible changes in friction on the boundaries of contact surfaces.

Inaccurate positioning can create undesirable loading of the sheet being gripped and excessive loading of the robot wrist and vacuum gripping elements. 

Figure 3. Computer model of the suction cup: The classic dynamic analysis computer simulation used the finite-element method. An adequate numerical model of the standard suction cup was created using TPU material properties.

It’s important to analyze deformation behavior of suction cups and basic loading types in the computer model for safe gripping.

Deformation analysis of suction cup

Suction cup load varies by the combination radial FRAD and axial FAX forces depending on gripping plane orientation. If the gripping system is insufficiently sized, especially if the safety coefficient is chosen incorrectly, these changes can result in a loss of contact stability and collapse when the suction cup is pulled off or the contact profile in the gripping plane shifts.

Figure 4. Friction coefficient values depend on material surface characteristics.

Boundary conditions describe the character of frictional conditions based on laboratory test results. Friction coefficient values depend substantially on the contact material surface (wet, dry, wet with oil, without oil).

The computer model was optimized for a variable active surface of the suction cup which, depending on the loading profile, is the effective diameter of the suction cup. Contact area corresponds to the loading level (contact quality) during each step of the calculation. Including this effect improved computer model accuracy for suction cup behavior during external loading.

Figure 5. Axial deformation of the suction cup, FRAD = FAX = 54 N, D = 100 mm: During computer simulation of the suction cup deformation behavior (the geometrical diameter of 60 mm), calculations were carried out. Suction cup deformation zones depend on the vacuum level (60 kPa) level and friction coefficient (f = 0.8) when combining the load with axial and radial forces at a point of the suction cup axis remote from the contact plane (D = 100, 150, and 200 mm).

Computer simulation results

Simulation results compared to outputs of laboratory experiments confirmed substantial agreement.

Multi-element gripping heads integrated with the service robot chassis can eliminate effects of tilting.

The computer simulation shows that particular suction cups loaded in the combined way can be deformed substantially, leading to considerable contact instability with adverse influences on the safety of object gripping and holding. Using more suction cups allows greater axial-force loading while tilting.

Figure 6. Axial deformation of the suction cup, FRAD = FAX = 54 N, D = 150 mm

A computer simulation can help with setup and improve operation of service robotics with mobile chassis, especially those used on vertical walls (such as autonomous washing and inspection activities at inaccessible places like high-rise buildings with glass casing/facade). This work resulted from Research Plan No. MSM 4674788501, funded by the Ministry of Education, Youth, and Sports of the Czech Republic. 

At a glance

  • computer simulation
  • suction cup
  • vacuum
  • combined load
  • safety coefficient

Marcel Horák and František Novotný are with Technical University of Liberec and contribute to Control Engineering Poland and Control Engineering Czech Republic. Reach them at marcel.horak(at)tul.cz, frantisek.novotny(at)tul.cz

www.tul.cz/en

www.controlengcesko.com

www.controlengpolska.com


Additional Areas of Interest

Global Perspectives: Power plant control system software - Performance calculation software packages are new in the power generation business and help with power generation control, electricity grid control, and monitoring via SCADA system. Courtesy: Control Engineering Poland.

Global Perspective: Hyper-Secured PLC…and other curious combinations - To make life easier for automation engineers, and less costly for OEMs and end-user companies to build control systems, clever companies are converging previously separate products, observes Control Engineering Europe.

Automation Conferences in Poland

In Poland, conferences bridge science and industry. Polish researchers need the practical testing of their ideas within real processes to uncover the pros and cons of the proposed solution. Automation companies look forward to cooperation with universities on research projects. Control Engineering Poland served as a media sponsor for the following conferences:

These conferences enable the possibility to present the highest quality works from the area of control engineering as well as mechanical engineering and mechatronics. This is among the best papers presented.

- Krzysztof Pietrusewicz, PhD, West Pomeranian University of Technology, Szczecin, Poland; Control Engineering Poland



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