Design and realization of grippers with permanent magnets

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Design and realization of grippers with permanent magnets

Peter Tuleja

Annotation

magnet pneumatic device

Urgency of the research. Modern production requires simple and inexpensive component solutions for gripping large parts. The design of gripping elements using a permanent magnet in this aspect is a promising direction.

Target setting. The aim of the project was to realize a gripping component from a commercially available pneumatic drive supplemented with a neodymium permanent magnet and to revive the resulting assembly with a pneumatic portal manipulation device designed for educational activities at the department.

Actual scientific researches and issues analysis. Implementation of the project required a detailed market research focused on the tentacles of a similar concept and the study of the principles and properties ofpermanent magnets. By analyzing the information the project objective was optimized - design of cheap and reliable gripping element.

Uninvestigated parts of general matters defining. Available components were used for the resulting solution, with an emphasis on low acquisition costs. This was due to the fact that the output was intended for laboratory use.

The research objective. The aim of the research was to build a realfunctioning and reliably working gripping device usable as an objectfor educational activities in the education of our students.

The statement of basic materials. Design and practical implementation of the grippers with permanent magnets for gripping parts represented in the work. Activation and control of the grips is implemented by compressed air. The implementation of the output confirmed the correctness of considerations as well as the feasibility of the repeatability of this output while meeting the basic requirement for low costs. The project was based on the principles offered by leading companies, but the implementation output gives a higher gripping force at lower input costs. In addition, it provides the possibility of extension to the size range according to customer requirements.

The project was successful and its implementation also contributed to the improvement of the educational process at the department, which was one of the monitored benefits. It provides an illustrative demonstration of the possibilities of performing manipulation tasks with non-standard objects.

When designing automated workplaces that require the handling of some specific types of objects of manipulation (Om), such as sheet metal or flat products (large dimensions in the X and Y axes of the basic coordinate system, but small dimensions in the Z axis), classical forms of gripping these objects cannot be used.

The technical solution is the principle of one-sided gripping. Perhaps the most common way of doing this is undoubtedly the manipulation with active vacuum suction effectors [5, 6]. However, some applications do not allow the use of vacuum, so they must be replaced by more appropriate methods.

This is how our solution was created as the output of the diploma thesis [1]. It is based on commercially produced effectors using a combination of compressed air and a permanent magnet to fixing the object of manipulation.

One-sided gripping. For automated Om manipulating, it is necessary to clearly define the handling task. This consists in executing a chain of operations related to changing the position of the Om in space, or changing its orientation in space, respectively both at the same time as a sequence of operations related to its grasp in the starting point, its fixation during the manipulation period and its release at the target site.

For this purpose, devices commonly called gripping effectors are used. Depending on the nature of action the gripping elements on the Om, there are effectors with two-sided grip (or more-sided grip), one-sided grip and a specific type of grip where there is no mechanical contact at all, Fig. 1.

Fig. 1. Gripping effectors according to the nature of contact with OM

Unlike double-sided (multi-sided) grasping, it is specific for unilateral grasping that the grasping effector's contact with the Om is often at only one point (unless the stability of the Om during the handling task is thereby impaired). If the force analysis for gripping by a single element does not suit, it is necessary to use a larger number (2 or more) of gripping elements and their arrangement should be solved by a suitable frame structure, Fig. 2.

Fig. 2. Frame construction for one-sided gripping elements [6]

The physical principles used for one-sided gripping are varied [6, 7], Fig. 3.

The most commonly used are active vacuum suction cups, but also magnetic grippers with electromagnets and permanent magnets.

The decisive factor for their choice is application suitability and of course price.

The suitability of the application relates to the suitability of the selected physical principle for gripping a particular Om (material and Om surface quality, surface integrity, surface division, etc.).

Fig. 3. Physical principles used in unilateral grip

General effector model. To describe any effector (not just a gripper) it is possible to use the general theory (theory of systems) about the system view of functional units and machinery.

The effector, as a technical system (assembly), is made up of elements (modules, functional nodes). It can be defined and described by a generalized system model, Fig. 4. It consists of functionally separate elements and modules and links [5]:

IFi flange connection to the robot IF2 connection with the effector device

Mm complementary motion micromechanism G gripping effector

C position and orientation compensator T tool (technological effector)

S special effector (combined)

Fig. 4. System model of the effector [4], edited by the author

Constructional designs of magnetic effectors [5] may have one of the system structures

IF1MMCIF2 - G

IF1MMIF2 - G

IF1CIF2 - G

IF1IF2 - G

The function of grasp - constriction - fixation of the passive gripper is accomplished by applying permanent magnets Mp in the gripper assembly G.

In the specific arrangement of our solution it is then possible to select the arrangement from the given classification

IF1MMCIF2 - G

The starting point of the solution was the gripping effectors by GOUDSMIT [2], Fig. 5.

Fig. 5. Passive magnetic gripper with pneumatic control by GOUDSMIT [2]

Similar solutions in their offer have eg. SMC, SCHMALZ and others. To compare our acceptance, we present selected parameters of these effectors, tab. 1.

Table 1. Comparison of selected parameters of magnetic effectors of world producers

Source of information: [2], [3], [4].

Project realisation. For the purpose of our solution, the concept of using the existing pneumatic compact drive CQ2B25-15D (SMC Corporation, Japan) [4] was used, on which a neodymium magnetic lens with a diameter of 20 mm and a height of 8 mm terminated with an M6 thread was mounted. This lens in a perpendicular direction provides a holding force of up to 140 N.

To eliminate the gripping force (release) between the Om and the magnet at the Om release location, the principle of detaching the lens from the Om by the force of the pneumatic drive was used. To add the Om in the place of its storage is used a separating body, which was produced by 3D printing. The assembly and the illustration of the effector are shown in Fig. 6.

Fig. 6. Pneumatically operated magnetic gripper

The total cost of building our concept did not exceed EUR 50. The supply pressure for the pneumatic drive required to detach the magnet from the Om was 0.5...0.6 MPa.

It should be emphasized that the effector was developed for demonstration purposes within the educational process at the department. therefore the figures given are for guidance only. A detailed analysis of effector characteristics (dynamic tests, etc.) is under preparation.

The gripping effector was used as an end effector on the laboratory pneumatic portal structure manipulation mechanism, Fig. 7.

Fig. 7. Pneumatic portal mechanism (a, b) and its control unit (c)

Perforated sheet blanks with dimensions of 100x60x2 mm were determined as Om's intended for manipulation with the effector.

The mechanism is controlled by the logic controller SIEMENS LOGO! (0BA6 ...). FBD handling cycle program built in LOGO! Soft Comfort v. 8.0 shows Fig. 8.

Since the withdrawal point of the handling mechanism is realized as an input with a human operator, one blank per one handling cycle is counted.

In order not to have to deal with special approach vectors of the manipulation device to establish sufficient contact of the effector with the Om, the compensator was applied as a separate mechanical structure defining the removal height during handling (compensation in the Z + direction), Fig. 9.

Fig. 9. 3D model of gripping effector assembly with compensator (a) and its real form (b)

The realization of the project from the assignment of the diploma thesis to the realization output in the form of an educational model (stend) took several years and went through several changes. Today, he is able to demonstrate in the process of teaching at the Department of Robotics in explaining the individual principles of gripping effectors working on the basis of one-sided gripping. There are other alternatives to unconventional one-sided gripping solutions (e.g. Bernoulli suction cup).

Acknowledgement. This contribution is the result of the project implementation: Research modules for intelligent robotic systems (ITMS: 26220220141) supported by the Research & Development operational Program funded by the ERDF.

References

1. Balockovв, Lenka, Tuleja P.: Nвvrh uchopovacej hlavice pre tvarovo zlozitй objekty. Diplomovв prвca. Kosice: Technickв univerzita v Kosiciach, Strojnicka fakulta, 2011. 61 s. (in Slovak).

2. https://www.goudsmitmagnets.com.

3. https://www.schmalz.com.

4. https://www.smc.eu.

5. Smrcek, J., Palko, A., Tuleja, P.: ROBOTIKA - Uchopovacie efektory, skriptum, TU v Kosiciach, 2007, ISBN 978-80-8073-961-4 (in Slovak).

6. Sukop M., Tuleja P., Janos R., Jurus O., Marcinko P., Semjon J., Vagas M.: Using the Vacuum in Handling Tasks in the Context of Operating Cost Savings. In: Journal of Automation and Control, 2017, Vol. 5, No. 2, pp. 85-88. Available online at http://pubs.sciepub.com/automation/5/2/12. © Science and Education Publishing DOI:10.12691/automation-5-2-12.

7. Tuleja P.: Technical Solutions of Problems in the Handling of the Object with Non-consistent Surface. In: American Journal of Mechanical Engineering, 2016, Vol. 4, No. 7, pp. 400-405. Available online at http://pubs.sciepub.com/ajme/4/7/31 ©Science and Education Publishing dOi:10. 12691/ajme-4-7-31.

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