The construction of a soft gripper based on magnetorheological elastomer with permanent magnet

Abstract

Recently, magnetorheological elastomers have become interesting smart materials with many new designs for robotics. Various applications have been built with magnetorheological elastomers, such as vibration absorbers, actuators, or valves, showing that this material is promising for industry applications. The objective of this study is to demonstrate that magnetorheological elastomers supported by a permanent magnet can create a soft gripper suitable for handling small and delicate objects such as fruits or candies. The novel concept of the gripper is proposed, exploring the features of a magnetorheological elastomer and a permanent magnet. This gripper uses the energy of a permanent magnet to provide a self-closing gripping mechanism. At the same time, the use of flexible material—elastomer allows it to hold delicate objects of various shapes. The effect of wrapping magnetorheological elastomer around a permanent magnet, the design process, and the characteristics of a soft gripper are presented. The effectiveness of the soft gripper was validated in a series of experiments that involved lifting various objects.

Keywords

magnetorheological elastomer magnetoactive elastomer soft gripper soft material permanent magnet

Introduction

In recent times, soft magnetic materials have gained significant attention in robotics and control systems due to their unique properties and potential for diverse applications (Erb et al., 2016; Eshaghi et al., 2021; Rateni et al., 2015; Ren et al., 2019). These materials, traditionally used in vibration control (Li et al., 2014; Lin et al., 2023), are characterized by their flexibility and ability to alter mechanical properties under the influence of magnetic fields. This has enabled their application in commercial devices such as vibration isolators and absorbers. However, their potential extends far beyond these uses. In the last decade, soft magnetic materials have been increasingly utilized in robotics for constructing haptic devices, soft grippers, and remote control of robots using external magnetic fields (Culha et al., 2020; Mahoney and Abbott, 2014; Popek et al., 2017).

Magnetorheological elastomers (MREs), as a subclass of soft magnetic materials, are particularly interesting for robotic applications. In the literature, two main types of MREs are described. The first type consists of an elastomer matrix mixed with soft magnetic particles, while the second type incorporates hard magnetic materials, granting the material its intrinsic magnetic field. The preparation processes and properties of these materials are well-documented (Bernat et al., 2022; Böse et al., 2021; Erb et al., 2016; Li et al., 2014). In our work, we focus on the first type of MRE, as its flexibility and responsiveness to magnetic fields make it suitable for soft robotic applications. Despite its advantages, MRE materials face challenges in robotic contexts due to their relatively low permeability compared to rigid magnetic materials like steel. This limitation requires stronger magnetic fields to produce significant deformations, as noted in previous studies (Böse et al., 2021; Cramer et al., 2018). While it has been suggested that further material improvements are needed to enhance performance (Cramer et al., 2018), our research demonstrates that MREs are already applicable for creating effective soft robotic grippers. Soft grippers have evolved significantly over the last decade (Navas et al., 2021; Pagoli et al., 2021; Rateni et al., 2015; Rus and Tolley, 2015; Shintake et al., 2018). These devices are commonly categorized by their actuation mechanisms, with pneumatic and mechanical systems being the most popular. Pneumatic grippers, such as PneuNet (Mosadegh et al., 2014) or particle jamming systems (Rus and Tolley, 2015; Washio et al., 2022), rely on variable pressure and require compressed air. Mechanical grippers, on the other hand, typically use cable-based mechanisms for actuation (Rateni et al., 2015). While these designs exhibit good performance, they are often limited by the need for complex control systems, such as air compressors or motors, which can reduce their portability. As a result, there is growing interest in exploring alternative actuation methods that offer greater simplicity and efficiency. For instance, dielectric electroactive polymers have been investigated as a potential solution, although they require high voltages for operation (Araromi et al., 2015; Shintake et al., 2015; Yoder et al., 2024). Magnetic energy presents an attractive alternative, offering high energy density per volume (e.g., in permanent magnets) and compatibility with soft materials.

In this context, magnetoactive materials, such as MREs, have emerged as promising candidates for constructing soft grippers. Several preliminary studies have explored their potential. For example, MRE-based grippers controlled by varying magnetic fields have been proposed to handle objects with adaptive capabilities (Choi et al., 2020; Skfivan et al., 2019; Zhang et al., 2021;). Other designs utilize MRE membranes for suction cups (Zhang et al., 2021) or adaptive skins for mechanical grippers (Choi et al., 2020). However, these designs often require external energy input or complex control systems, limiting their practicality. Some studies have explored MREs as auxiliary materials, such as in magnetorheological fluid bladders or in combination with shape memory alloys (SMA) to enhance performance (Choi et al., 2018; Yang et al., 2022). Despite these efforts, the full potential of MRE materials, particularly in terms of self-actuating capabilities, remains underexplored.

In our work, we propose a novel design concept for an MRE-based gripper that leverages the interaction between a permanent magnet and an MRE strip. This innovative geometry enables a self-closing mechanism, reducing the need for external energy input in the gripping state. Compared to previous designs (Bernat et al., 2022; Böse et al., 2021; Choi et al., 2020; Cramer et al., 2018; Guan et al., 2022; Skfivan et al., 2019; Zhang et al., 2021), our approach exploits a new effect of magnetic torque to achieve both simplicity and functionality. To validate this concept, we fabricated a prototype gripper and conducted experiments demonstrating its effectiveness. This study aims to showcase the viability of MRE materials in robotic applications, overcoming limitations previously noted in the literature and paving the way for more compact and efficient soft robotic devices.

The gripper concept

This section elaborates on the gripper design introduced earlier, based on the interaction between a magnetorheological elastomer strip and a cylindrical permanent magnet. The first is elastomer material with soft magnetic particles. Its main features are flexibility and reactive to the electromagnet field. The second is a permanent magnet that stores a lot of magnetic field energy. In our work, we used these elements to create a self-closing mechanism.

The magnetic self-closing mechanism

The main idea of the gripper is based on the magnetic self-closing mechanism created with the MRE strip and a cylindrical permanent magnet. Its working principle is illustrated in Figure 1(a) and (b). The magnetic field of the permanent magnet causes MRE to be screwed onto the permanent magnet. The behavior can also be simply checked by experiment using the MRE strip and a permanent magnet with fixed rotation axes, as shown in Figure 1(c).

To show that the connection of the MRE strip with the permanent magnet produces the rotating torque, simulations were performed using ANSYS 2023 R1. The example of the field is shown in Figure 1(d) where the figure presents the magnetic field in MRE strip. It can be seen that the volume that contains the magnetic field is increasing with the MRE winding up on the permanent magnet. Therefore, the torque is produced as long as the MRE is not wrapped around the permanent magnet.

The torque characteristic was calculated using the virtual work principle (Carpentier et al., 2014; Ren and Razek, 1992). The general expression for the coenergy is given as:

W_{co} (θ) = \int_{V} (\int_{0}^{H} BdH) dV

(1)

where $θ$ describes the angle between MRE and permanent magnet (presented in Figure 1(a)), $V$ is the volume of the analyzed object, and $H$ , $B$ are the magnetizing field and magnetic field respectively found by solving Maxwell’s equation in the FEM software. The torque can be found by the derivative of the coenergy:

τ_{mre - pm} (θ) = \frac{\partial W_{co} (θ)}{\partial θ}

(2)

with respect to $θ$ . In our work, in the first step, the coenergy of MRE strip and the permanent magnet was found for a range of $θ$ angle using ANSYS software. Then, to eliminate numerical errors in solving Maxwell’s equation, it was approximated by a spline function, as shown in Figure 1(e). Finally, the torque $τ_{mre - pm} (θ)$ was found by calculating the derivative. The results are visible in Figure 1(f). It is clear that the torque for the angle between 0° to 225° is almost constant. If the MRE strip is almost all wrapped around the permanent magnet, then the torque is going to 0.

The gripper construction

In general, the gripper concept is based on the use of three fingers constructed from an MRE strip and a permanent magnet. The field energy stored in a permanent magnet causes self-closing of the gripper finger as discussed in the previous section. The switching between open and closed state is controlled by a single linear electromagnet actuator.

The working principle of a single finger is as follows. In the open state (Figure 2(a)), the electromagnet plunger is extended, so the construction frame with a permanent magnet goes down, causing the MRE finger to be straight. In the closed state (Figure 2(b)), the electromagnet plunger is inserted, so the permanent magnet goes up and hence the MRE finger is wrapped around the permanent magnet. In this point, the self-closing mechanics, discussed in the previous section, play a crucial role by closing the finger.

The soft gripper is made with three fingers as shown in Figure 2(c). The electromagnet controls the position of the magnet frame with permanent magnets. Therefore, all fingers are controlled by a single electromagnet, and the gripper has only an open/closed state. Furthermore, the MRE strips have a small triangle near the handle object for a better grip, as visible in Figure 2(c).

The gripper holds objects in the space between the fingers. The size of the gripped objects depends on the position of permanent magnets and the size of MRE fingers. In Figure 2(d) two marked circles show the space for cylindrical objects in the open and closed state. In the open state, objects are bounded by permanent magnets, which are shown by a circle with radius $r_{open}$ . The following relationship $r_{open} = r_{frame} - \frac{1}{2} d_{PM}$ describes the connections between radius in the open state, mounting frame radius (place for the center of permanent magnets) $r_{frame}$ and permanent magnet diameter $d_{PM}$ . In the closed state, the three fingers are touching each other. Therefore, the objects are bounded by MRE fingers of minimal size given by a circle with radius $r_{close}$ . The equilateral triangle relationship connects the $r_{close}$ with the width of the finger, so $r_{close} = \frac{\sqrt{3}}{6} w$ where $w$ is the width of the MRE finger.

Preparation of magnetorheological elastomers

The MRE material was prepared according to the procedure described in (Bernat et al., 2022). A brief description of the methodology for preparing MREs is given below. The described preparation process is presented in graphical flow chart in Figure 3. Three silicons with different properties were used to prepare MRE. These were Mold Star 15 (MS15) and Dragon Skin 10 (DS10) (both from Smooth-On) and RTV (OTT-S825 from OTTSilicone). The iron powder with an average particle size of 63 μm (99%, Sigma-Aldrich) was weighed in a glass container and thoroughly mixed with each silicone until a homogeneous mixture was obtained. The weight ratio of silicone to iron powder was equal to 1:1, thus iron powder constitutes 13% by the sample volume. Then, in the case of RTV silicone, the catalyst was added in an amount of 2% by weight relative to the amount of silicone. The MS15 and DS10 are two-component silicons in which one of the components already contains a catalyst. After thorough mixing, the resulting mixture was degassed by vacuum treatment. Finally, the mixture was poured into the mold presented in Figure 4(a). After 24 h, the MRE material was removed from the mold and carefully checked for bubbles in the structure. In the next step, the mixture of silicone with iron was prepared with the same procedure as before and the second part of the gripper was prepared (Figure 4(b)). Both parts of the mold were made by 3D printing. The final gripper finger is presented in Figure 4(c).

The experiments

This section describes a series of experiments to verify the proposed concept. Firstly, the fabrication of the gripper is discussed and then its validation is described.

Gripper fabrication

The gripper, designed as described in section “The gripper concept,” was fabricated using three MRE strips and three permanent magnets mounted on a frame by a linear electromagnet. Detailed construction parameters including finger geometry and open/closed radius $r_{open} =$ = 8 mm and $r_{close} =$ = 4.33 mm are presented in Table 1.

Table 1.

The MRE finger dimensions, electromagnet (EM), and neodymium permanent magnet (PM) properties (based on the manufacturer’s datasheet).

Name (symbol)	Value	Unit
MRE finger width ( $w$ )	15	mm
MRE finger length	60	mm
MRE finger thickness	2–4	mm
Mounting frame radius ( $r_{frame}$ )	18	mm
EM move range	12	mm
EM rated current	0.7	A
EM rated voltage	12	V
EM max load	3.5	kg
PM inner diameter	4.2	mm
PM outer diameter ( $d_{PM}$ )	20	mm
PM thickness	5	mm
PM field in the geometric pole center	0.355	T
PM hysteresis remanence ( $B_{r}$ )	1.21–1.25	T
PM hysteresis coercivity ( $H_{c}$ )	899	kA/m

The gripper is constructed of three MRE strips, three permanent magnets, a linear electromagnet, and a frame created by additive manufacturing. The parameters of the MRE finger, linear electromagnet, frame, and permanent magnet are provided in Table 1. Relying on them and the open/closed radius presented in Figure 2(d) is equal to $r_{open} =$ = 8 mm and $r_{close} =$ = 4.33 mm. Movement of the frame with permanent magnets is ensured by a linear electromagnet with a spring defined in Table 1. In our gripper, the input signal is the voltage applied to the electromagnet. The turn on the gripper causes its closing and the turn off causes its opening. The concept of the gripper is presented in Figure 5(b), where the most important elements such as electromagnet (the element that allows controlling gripping process), permanent magnets (which allow rolling around them) and MREs (a crucial part of the gripper that allows gripping objects using its magnetic abilities and makes the gripper soft) are marked.

Mechanical properties and morphology of silicons and MREs

The mechanical properties, that is, tensile tests, of individual silicones and MREs made on their basis were examined to connect the properties of the obtained MREs with their action as actuators. Pure silicone samples (DS10, MS15, RTV) and MREs obtained from them were prepared as bars with dimensions of 50 mm length, 15 mm width, and 2 mm thickness. The tests were carried out on Universal Testing Machine Zwick Roell Z020 at a traverse speed of 5 mm/min up to 30% of sample strain for Young’s modulus ( $E_{\mod}$ ) determination, and 50 mm/min for the remaining part of the test in order to determine the stress value at 100% ( $σ_{100 %}$ ) and 300% ( $σ_{300 %}$ ) sample strain. The initial force was 0.05 N.

The morphology of silicones and MREs samples was studied using a JEOL 7001F scanning electron microscope (SEI detector, 5 kV accelerating voltage). Before measurement, the samples were cut, and the small pieces of each sample were placed on a piece of metal with adhesive and then coated with an ultrathin Gold coating, deposited on the samples by a low-vacuum spray method. The cross-section of the prepared samples was tested.

Validation

The aim of the validation process was to verify the basic principle of the gripper operation, its holding possibility of various objects, repeatedly holding process, and measure the gripper finger pushing force.

The validation of the gripper was conducted by a series of experiments with the gripper mounted on the KUKA manipulator (KR 6 R900). Figure 6(a) and (b) show two states of this device: (Figure 6(a)) this is the first situation when the gripper is open, whereas (Figure 6(b)) shows what happens when the gripper is closed and the rolling effect around the permanent magnets is visible. In Figure 6(b) it can be seen that the rolling around of the MRE strips causes them to come closer to each other and at this point, the grip occurs. According to Figure 2(d) the radius $r_{closed}$ can be slightly lower due to the possibility of compressing MRE finger corners when touching.

An additional experiment was conducted on the single gripper finger to get to know the force acting in the closed state. The gripper with two fingers removed was set up with the force sensor (Axis FB20) as presented in Figure 7(a). The gripper was turned on/off 5 times. Each time, in the closed gripper state the force was read from the sensors. The average force is $0.7 \pm 0.02$ N and it shows that gripper fingers produce force when they are rotated on permanent magnets. In the next experiment, the finger was in the closed state, and the force sensor was set up almost touching. Then, the robot was moved with 1 mm steps touching the force sensor. Experiments consisted from 4 series. Based on collected data mean and standard deviation for each material type is calculated and marked on the Figure 7(b). As can be seen from the resulting characteristics visible in Figure 7(b) all materials have almost the same characteristics.

The experiment showing the operation of the gripper, its maximum gripping range, and lifting capacity was conducted on six different objects. Table 2 presents the specification of lifting elements (in the case of irregular shape, diameter describes the outer outline). All elements were successfully gripped 10 times for 10 attempts (only the bilberry has an 8/10 ratio). The overall success rate of gripping is equal to 96.6%. The maximum mass of the lifted object was 28 g (brass element). The speed of closing or opening of the gripper was estimated based on the movie. The closing time is about 150 ms and opening time is about 175 ms.

Table 2.

Lifted elements with their mass and dimensions.

Name (Figure)	Mass (g)	Dimension (mm)
Grape (8(a))	2.5	H = 18, D = 15
Bilberry (8(b))	2	H = 13, D = 16.5
Candy (8(c))	16.34	H = 40, W = 25, L = 17
Silicon hat (8(d))	2.75	W = 25, H = 28
Brass element (8(e))	28	H = 25, D = 22
White ball (8(f))	2.07	D = 20

W: width; L: length; H: height; D: diameter.

What is very important all photos in Figure 8 were taken in the same camera position, and gravity acts vertically downwards. As presented, the orientation of the gripper does not affect gripping ability (so it is independent of gravity). The properties of MRE, its rough surface, and the strong magnetic force result in a firm gripping effect, which means that all types of elements used for validation did not slip out.

Finally, all materials were tested to find the maximum weight the gripper could hold. The tests were performed with brass elements with attached additional metal washers as it is visible in Figure 7(c). Table 3 shows that the MRE prepared with RTV silicone can lift the largest mass, while the MRE prepared with DS15 silicone can lift the smallest mass, which is 2.4 times smaller than in the case of MRE with RTV silicone. The obtained results can be related to the mechanical properties, more precisely the tensile strength, of the obtained MREs. With the increase of stiffness (higher $E_{\mod}$ values) and strength of materials (higher values of $σ_{100 %}$ and $σ_{300 %}$ ), the maximum mass that can be lifted by the gripper made of MREs increases. This can be attributed to the fact that the material with higher stiffness, from which the gripper is made, deforms to a lesser extent after lifting the object due to its lower elasticity. Hence, the mass of the lifted object can be higher.

Table 3.

The mechanical properties of pure silicones and MREs for RTV, MS10, and DS15 silicones. In the last column, the maximum mass lifted by the gripper with MRE fingers.

Name	$E_{\mod}$	$σ_{100 %}$	$σ_{300 %}$	Max. mass
	(MPa)	(MPa)	(MPa)	(g)
Pure RTV	0.52	0.87	—	—
Pure MS10	0.45	0.72	4.54	—
Pure DS15	0.22	0.28	2.13	—
MRE with RTV	0.81	1.64	—	97.4
MRE with MS10	0.78	0.93	4.04	86.5
MRE with DS15	0.36	0.48	2.24	40.2

Analyzing the SEM images of the Dragon Skin silicone (other silicones have similar surfaces) shown in Figure 9(a), it can be seen that the silicone matrix is smooth and no air bubbles are observed in it. Therefore, the deaeration process during sample preparation was good enough. Additionally, analyzing the morphology of the obtained MREs (Figure 9(b)–(d)), regardless of the type of silicone matrix, the iron dispersion is homogeneous and no filler aggregates are observed. The filler grain size is smaller than the value given by the manufacturer (63 μm) and is in the range of approx. 10–60 μm. The holes appearing in the modified systems are the result of tearing out the hard filler from the flexible polymer matrix during sample preparation. Additionally in Table 1s and Figure 1s, the measurement of inductance is shown to present the magnetic properties of analyzed samples.

Comparison to non-magnetic finger

In this section, the comparison of MRE strip and the permanent magnet with a pure silicone strip bonded to the non-magnetic cylindrical bearing is described. The purpose of this comparison is to highlight the advantages and new features of the gripper finger in our design.

Based on the reviewer’s suggestion we prepared a simulation with a finger design in which we tested the behavior of a strip made of RTV silicone attached to a cylinder (by glueing, for instance). The simulation in Anys Mechanical 2024 R1 worked as follows. Initially, an input force was applied on the top of the MRE strip to represent the closing finger by an electromagnetic actuator. Then, a load force was added, representing a finger-pressing object, to the bottom end of the MRE strip. The resulting deformations are presented in Figure 10 (detailed version is in Figure 2s). It is clearly visible that the load force is shown in Figure 10(b) strongly bends the MRE strip. This is due to the lack of the MRE-PM force, which adds tension to the MRE strip. In the design proposed in this study, the permanent magnet pulls the MRE strip, and this keeps the finger under tension at all times, regardless of the point at which the finger is attached. The same force also forces the finger to press against objects with a constant value. If there were no additional forces due to the reaction of the MRE strip and the permanent magnet, the finger would deform, with the consequence that the finger would have to be pushed with great force to compensate for the elastic force and move the tip of the finger (as visible in Figure 10(b)).

Additionally, in Figure 11, it can be read that the combination of MRE-PM gives more force at the same displacement compared to the MRE strip alone (with nonmagnetic bearing). A bonded strip must be compressed more firmly than an MRE strip connected to a permanent magnet to respond with comparable contact force. In the case of MRE-PM strips, the contact force from the offset is less dependent on the material of the strip. The MRE-PM characteristics for different Young’s moduli are closer together than those of bonded strips. This allows the load force on the object to be constant regardless of the softness of the material. The details of simulation results and additional figures from the experiments are shown in the Supplemental Material. Especially, the experimental result showing that the MRE strip has large deflection under the force application can be seen in Figure 3s. The experiment performed is to confirm whether the belt will behave similarly to the simulation. The measured force of the MRE strip is 0.4 N, which is lower than the force obtained using the combination of the MRE strip and the permanent magnet, which was 0.6 N. In supplementary material, the schema of both configurations is shown in Figure 4s.

Discussion

In the presented gripper, the object grasping is based on the interaction between a permanent magnet and a magnetorheological elastomer strip. The combination of magnetorheological elastomer winding up on the permanent magnet for creating the gripper is a novel concept from the point of view of the author’s knowledge in literature (Bernat et al., 2022; Böse et al., 2021; Choi et al., 2020; Cramer et al., 2018; Guan et al., 2022; Skfivan et al., 2019; Zhang et al., 2021).

In general, the comparison of soft grippers’ quantitative indicators like lifting mass is difficult due to their variety of geometry and size—all grippers presented in works (Bernat et al., 2022; Choi et al., 2018, 2020, 2023; Guan et al., 2022; Skfivan et al., 2019; Zhang et al., 2021) have different properties. In most cases, the same gripper design can be scaled to be larger or smaller to obtain different indicators.

In this work, the presented construction can create a normally open or closed state, and hence it does not require direct power to hold objects or to be opened. Furthermore, from the author’s point of view, the gripper is easy to produce with commonly accessible materials. The gripper is controlled by voltage excitation, which is easily accessible and has a fast response time. It has a much larger maximum load capability (up to 10 times greater) in comparison to the finger-based grippers defined in work (Bernat et al., 2022; Guan et al., 2022). Alternatively, the soft gripper based on the suction cup (Zhang et al., 2021) has a lifting ability of about 300 g with a current of about 10 A, but this kind of gripper cannot manipulate objects (has no fingers). In our case, we energized the electromagnet 12 V and 0.7 A, which makes our gripper more energy efficient.

Furthermore, in our solution, the behavior of the gripper fingers does not depend on the direction of gravity. Relying on the experiments, it was visible that the gripper process is very stable. This means that the gripper catches the object on the first try in most of the experiments. Furthermore, the speed of the gripper is very fast in comparison to work (Skfivan et al., 2019) (up to 4 times).

Soft grippers are constantly being developed and new scientific research related to this topic is conducted. Our work presents an alternative solution to the problem of gripping soft, delicate, and small objects. Each type of gripper has its own advantages and disadvantages depending on the environment in which it operates and the object being gripped. Our gripper combines the features of a rigid structure and soft all-silicone fingers. PneuNet grippers with long fingers can deform under gravitational force, which can impose some restrictions on the orientation in which the gripper operates. The fingers hang in the direction of the gravitational field. In the case of our gripper, this effect does not occur due to the presence of short fingers and magnetic force. On the other hand, grippers with tendons require a rigid structure so that the fingers are not fully soft and do not adapt to the object being gripped in the same way as silicone grippers. The gripper design, in which the fingers act as tendons (presented in section “Comparison to non-magnetic finger”), proved to be less effective than the MRE-PM design proposed by us. We believe that casting MRE components for our gripper is easier than casting components for a PneuNet-type gripper. Our pile is an internally filled strip. In PneuNet grippers, care must be taken to ensure that the channels through which the air moves are not blocked. We think that we will be able to achieve a high degree of miniaturization in the future by optimizing the shape of the design. In this paper, electricity was used to power the system. However, the construction of the MRE-PM does not force the use of this particular medium, making it susceptible to modification. Our gripper obviously has disadvantages, but we believe it can be significantly improved in future.

In further work, it is possible to independently control each gripper finger. This gives the ability to manipulate objects in a more sophisticated way than just grabbing objects. Furthermore, the authors believe that maximization of the gripping force by providing anisotropy to MRE material with shape optimization is possible because the study on the anisotropy in MRE materials has shown improvement as summarized in work (Böse et al., 2021).

Conclusion

In summary, the presented work introduces magnetorheological elastomer winding up on the permanent magnet, which is a novel mechanism in contrast to previous soft magnetic robots presented in the literature. The proposed mechanism is applied to construct a novel soft gripper. The main advantages of the proposed soft gripper are as follows. It is simple to build with readily available materials. As demonstrated in the experiments, it can hold various items, such as 3D-printed elements, a ball, a silicon cap, or brass elements. The overall success rate of gripping is almost 97%. The gripper can hold an element weighing up to about 97 g, which is enough to lift small everyday-use objects like fruits or candies. In addition, the use of soft fingers allows you to grab delicate items.

In the MRE-PM configuration proposed in the work, we use the self-wrapping of the MRE strip around the magnet. The wrapping of the MRE strip around the permanent magnet generates a moment of inertia that stiffens the strip, adding additional force to the system, which allows us to apply more pressure to the object to be grasped. The use of our design allows us to apply more force and effectively use a soft finger, for instance, compared to the bonded version.

We hope that our design will also find other applications in the future. Perhaps in space technologies, where variable environmental conditions such as temperature and pressure can affect pneumatic systems. In such conditions, a reliable design that is easy to assemble and disassemble may be required. The gripper shown in the article is a prototype for a novel soft magnetic gripper design. With this publication, the advantages and disadvantages of our design can be identified, and the corresponding gripper features can be optimized. The future improvements are replacing short fingers with longer ones, introducing anisotropy to geometry or design fingers to work independently.

Supplemental Material

sj-pdf-1-jim-10.1177_1045389X251362386 – Supplemental material for The construction of a soft gripper based on magnetorheological elastomer with permanent magnet

Supplemental material, sj-pdf-1-jim-10.1177_1045389X251362386 for The construction of a soft gripper based on magnetorheological elastomer with permanent magnet by Jakub Bernat, Paweł Czopek, Piotr Gajewski, Agnieszka Marcinkowska and Paulina Superczyńska in Journal of Intelligent Material Systems and Structures

Footnotes

Acknowledgements

The authors would like to thank dr Paweł Szulczyński for his help in conducting experiments with a KUKA robot.

ORCID iDs

Jakub Bernat

Paulina Superczyńska

Funding

The authors disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research was funded by the Ministry of Education and Science, grant number 0211/SBAD/0125 and 0912/SBAD/2503.

Declaration of conflicting interests

The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Data availability statement

Data sharing not applicable to this article as no datasets were generated or analyzed during the current study.

Supplemental material

Supplemental Material for this article is available online.

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