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This figure shows the types of friction based locking devices with: (a) a bi-stable brake, (b) an overrunning clutch, (c) a piezo actuated brake, (d) a statically balanced brake, (e) a wormwheel, (f) a self-engaging brake, (g) a thermic lock, (h) a self-engaging pinion-gear mechanism and (i) a capstan.
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Locking devices are widely used in robotics, for instance to lock springs and joints or to reconfigure robots. This review article classifies the locking devices currently described in the literature and performs a comparative study. Designers can therefore better determine which locking device best matches the needs of their application. The locki...
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... overrunning clutch has an inner and outer raceway simi- lar to bearings, with cylinders or balls (rollers) between the two raceways and a wedge on one side (see Fig. 3b). The relative rotational speed of the two raceways determines whether the overrunning clutch locks or not. The rollers of an overrunning clutch can also be pushed in the wedge using small springs or an actuator. The equivalent linear locking device uses a friction lever which is mounted around a translating stick. When this friction ...
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... gearing are gears that can only be driven from one side. In robotics, mostly lead-screw and worm drives (see Fig. 3e) have been employed. The non-backdrivability is due to the shear friction, which also results in a very low efficiency. As a result, non back-drivable gears are passive locking ...
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... locking devices used in robotics are based on self amplifying brakes (see Figs. 3f and 3h). While only a small force is required to engage both sides of the brake, the self amplifying effect enables to lock high forces. The self amplifying effect depends on the direction of the relative motion between the two components of the mechanism. In one direction, the mechanism will amplify the normal force since the friction ...
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... In one direction, the mechanism will amplify the normal force since the friction between the two friction surfaces will pull them together. In the other direction, the mechanism will weaken the normal force and will therefore not lock as strongly. As such, this principle is suitable for one-direction locking only. An example of this is shown in Fig. 3f. When the small force to engage both surfaces is delivered by a spring, the amplifying brakes are passive. When this is delivered by a motor, the amplifying brakes are active and allow to not lock in either of both directions. The applications found in literature are active self ampifying brakes. Kim and Choi [59] used an active self ...
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... in literature are active self ampifying brakes. Kim and Choi [59] used an active self amplifying brake for an automotive clutch. In their clutch, the normal force is amplified by a wedge-like pinion gear mechanism, which transfers a relative rotational motion into a small translational motion, pushing the friction plates stronger together (see Fig. 3h). Peerdeman et al. [60] used an active self amplify- ing mechanism in their underactuated robotic hand to lock the joints of the fingers in order to perform certain grasps. This application is similar to the robotic hand discussed in section ...
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... special type of a self amplifying brake is the capstan. Capstans use the friction between a pulley and a cable to brake the cable with respect to the pulley (see Fig. 3i). When the cable is tightened around the pulley, the pulley pulls on the cable, which tightens the cable even more. In robotics, a capstan is mainly used as a means to actuate a cable. Werkmeister et al. [61] and Baser et al. [62] studied the capstan drive stiffness and slip error respectively. A capstan cable drive is used, for ...
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... actuated brakes use piezo actuators to create a normal force between two friction surfaces (see Fig. 3c). These actua- tors typically have a small stroke and therefore the alignment of the components is crucial. However, they are suited for generating a large force for a large amount of time, making them suitable for actuating brakes. The idea of a piezoelectric brake was already patented in 1989 by Yamatoh et al. [76] and was also used ...
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... way to reduce the actuation needed for maintaining the normal force in friction based locking devices is using a bi-stable mechanism (see Fig. 3a). Such a mechanism has two stable equilibrium positions with one unstable equilibrium position in between. It doesn't require force once the mech- anism is switched, but it does require force to switch from one side of the unstable equilibrium position to the other and is therefore an active locking device. In bi-stable brakes, this ...
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... friction based locking mechanism that completely decou- ples the friction force and the actuation force is the statically balanced brake by Plooij et al. [83] (see Fig. 3d). This brake comprises three groups of springs of which the total potential energy is constant. Therefore, all positions of the brake are equilibrium positions, while the position of the brake determines the normal force between the two friction surfaces. Since the actuator now only has to apply a force to move a small part, the energy ...
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... thermic lock uses the difference in thermal expansion coefficients of different materials to obtain a lock with force closure (see Fig. 3g). The mechanism consists of a shell that can freely rotate around a core. The material of the core has a higher thermal expansion coefficient than the shell. The temperature control is achieved by a resistance wire that heats up the brake and which then locks the joint. Since heating up and cooling down take time, the response time of ...
Citations
... To further extend the workspace of the mechanism, it is possible to dynamically change the kinematic constraints on the platform through the use of motors equipped with drums and locking devices [24] intended for changing and remaining the constrained cables' lengths. The resulting mechanism is shown in Fig. 1(b), in which the motors are classified into two types: ...
... For example, to reduce the transition time, it is possible to control the driving cables and the constrained Fig. 13 A possible outdoor application of the DCCDR cable that slacks simultaneously during the motion and/or to control two or more constrained cables simultaneously by taking type 3 (in this case, the mechanism is fully actuated) and type 4 (in this case, the mechanism is underactuated) transformations into account. Moreover, this work only considers ideal lockers (i.e., the auxiliary motors can be locked at any pose of the platform [24]), for discontinuous lockers, the transformation poses where the auxiliary motors are required to be locked should be selected properly. The design and motion planning concepts are not limited to solving the problems studied in this work. ...
Extending the workspace of cable robots can enhance their motion ability and help us make fuller use of their potential. This work designs a novel cable robot and utilizes cable slack-ness to extend its workspace. First, we use driving cables actuated by main motors and constrained cables driven by auxiliary motors equipped with lockers to control and restrain the motion of the end-effector, respectively. Then we classify the constraints on the end-effector into different modes according to the slackness of different constrained cables whose lengths can be changed by auxiliary motors, and continuous tension distribution (realized by tensioning devices) is applied to switch among them. To expand the mechanism's work-space, the properties of the constraint mode series are analyzed and the static reachable workspace associated with it is defined, which guarantees the existence of feasible point-to-point trajectories. In particular, tree-based basic and general constraint mode series connection algorithms are designed to connect two targets in the static reachable work-space efficiently considering the necessary condition for the existence of the connection. After that, dual workspaces and subspace-based motion planning algorithms are designed to connect multiple targets in the static reachable workspace of the mechanism, and the quality of the trajectories is improved by using different manipulations of the constraint mode series. Since only driving cables are actuated by real-time capable servo motors and passively constrained cables are adopted to compensate for the weight of the end-effec-tor, the size and the number of actuators and the energy consumption of the robot are reduced. Finally, the performance of the mechanism designed and the motion planning methods proposed are verified numerically under practical modeling errors regarding the cable elongation phenomenon.
... The conventional approach to achieving full control over a system involves using one or more motors to fully actuate each DoF [1,2]. However, employing one motor per joint is often heavy and power-intensive, especially in high-DoF systems, and has been criticized by some designers and researchers [3,4,5,6]. A potential solution to this issue can be found by drawing inspiration from electronics, particularly electrical multiplexing. ...
... Mechanical multiplexing can be realized using clutches, which help reduce weight and power consumption in one of two primary ways: as part of a mechanical multiplexing system or as a mechanism to hold the position of a system [3]. In mechanical multiplexing, power is distributed among multiple outputs, thereby decreasing the number of actuators required and achieving significant weight and power savings. ...
This paper introduces a novel mechanical multiplexing system powered by electrostatic capstan clutches, enabling high-force, single-motor control of multiple degrees of freedom (DoF). The system is capable of both bidirectional single-input single-output time-division and single-input multiple-output multiplexing to actuate a commercial 4-DoF robotic hand with a single motor. Our mechanical multiplexer is also capable of powerless position holding owing to its use of a leadscrew nut acting as the output. Experimental results demonstrate the effectiveness of this approach, achieving individual and simultaneous actuation. This innovation offers a scalable solution for high-DoF robotic systems, providing a path to efficient actuation in robotic platforms.
... In [29], it was also found that even very low frequencies may influence failures under cycling load in what the authors called a creep-slip phenomenon. In a review work by Plooij et al. [30], three different locking mechanisms (to avoid such reduction in the frictional forces) were introduced: mechanical locking, friction-based locking, and singularity locking. The prevention of failure in the relative bolt connections is the focus of the work of [31]. ...
... The results indicate that the closer the deformation field is to the hub due to the impulse, the greater the change in contact pressure and the associated drop in torque. In addition, the results may differ with different natural frequencies of the shaft or a different impact energy which causes different transverse vibrations and may arise in different locking mechanisms in the connection [30]. Figure 12 is showing the simulation result in which the impact ( 1.6 kg , 3000 mm s ⁄ , 1.9 J ) was initiated three times at the same position during the captured time. ...
... The results indicate that the closer the deformation field is to the hub due to the impulse, the greater the change in contact pressure and the associated drop in torque. In addition, the results may differ with different natural frequencies of the shaft or a different impact energy which causes different transverse vibrations and may arise in different locking mechanisms in the connection [30]. In Figure 13, the influence of the distance between the hub and the point of impact (ℎ) on the transmittable torque is shown. ...
A well-known phenomenon in machinery systems is the easing of a blocked connection of mechanical parts after an impact hit close to the connection. Such impact hits may also arise in shaft–hub connections such as gears, crankshafts, or other parts. The objective of this study is to investigate the influence of local impact loads on the transmittable torque of smooth shaft–hub connections. In a specially designed test rig, it was demonstrated that the transmittable torque of the shaft–hub connection is reduced as a consequence of the impact, resulting in a reduction in the frictional force and slippage of the hub. Increasing the impact load leads to an increase in the reduction in the frictional force as well as the slippage and reduces the transmittable torque. By carrying out a modal analysis of the relevant parts and FE simulations of the impact, two possible reasons have been identified: (i) the impact load excites a vibration mode in the connection which reduces the frictional force and the transmittable torque; and (ii) the impact causes local deformation of the shaft, which results in local slip.
... Even in 4D structures, where shape change is triggered by environmental stimuli, an ongoing external force is often required to sustain the new configuration. To minimize the requirement for a continuous energy supply to uphold a structure's geometry, locking mechanisms are occasionally utilized to secure these structures in the desired configuration [17][18][19] . However, these structures are not able to hold their changed morphological position by themselves. ...
Inspired by the starfish's unique ability to achieve flexibility and posture-holding with minimal energy expenditure, we present a novel bioinspired morphing structure. Our two-component design, consisting of a thermoplastic mesh and elastomeric jacket, effectively mimics the functions of the starfish's ossicles, mutable collagenous tissues, and derma. This structure exhibits a remarkable combination of self-healing, time-dependent shape memory, and self-posture-holding properties. Systematic variations in mesh geometry demonstrate precise control over structural stiffness and thermal response, enabling customization for specific applications. The structure's scalability and ease of fabrication further enhance its adaptability. We experimentally demonstrate the potential of our biomimetic morphing structure using several prototypes. This work lays the foundation for developing a new type of versatile morphing structures with applications in diverse fields, including robotics, biomedical devices, and adaptive structures.
... Existing clutches [22] are mostly rigid. While pneumatic and vacuum jamming clutches can be soft, they require bulky pumps and valves. ...
Artificial muscles play a crucial role in musculoskeletal robotics and prosthetics to approximate the force-generating functionality of biological muscle. However, current artificial muscle systems are typically limited to either contraction or extension, not both. This limitation hinders the development of fully functional artificial musculoskeletal systems. We address this challenge by introducing an artificial antagonistic muscle system capable of both contraction and extension. Our design integrates non-stretchable electrohydraulic soft actuators (HASELs) with electrostatic clutches within an antagonistic musculoskeletal framework. This configuration enables an antagonistic joint to achieve a full range of motion without displacement loss due to tendon slack. We implement a synchronization method to coordinate muscle and clutch units, ensuring smooth motion profiles and speeds. This approach facilitates seamless transitions between antagonistic muscles at operational frequencies of up to 3.2 Hz. While our prototype utilizes electrohydraulic actuators, this muscle-clutch concept is adaptable to other non-stretchable artificial muscles, such as McKibben actuators, expanding their capability for extension and full range of motion in antagonistic setups. Our design represents a significant advancement in the development of fundamental components for more functional and efficient artificial musculoskeletal systems, bringing their capabilities closer to those of their biological counterparts.
... To further extend the workspace of the mechanism, it is possible to dynamically change the kinematic constraints on the platform through the use of motors equipped with drums & locking devices [32] intended for changing and remaining the constrained cables' lengths. The resulting mechanism is shown in Fig.2(a), in which the motors are classified into two types. ...
... E.g., to reduce the transition time, it is possible to control the driving cables and the related constrained cable simultaneously during the motion, and/or control two or more constrained cables simultaneously by taking type 3 (in this case, the mechanism is fully actuated) and type 4 (in this case, the mechanism is under-actuated) transformations into account. Moreover, this work only considers continuous lockers (i.e., the auxiliary motors can be locked at any pose of the platform [32]), for discontinuous lockers, the transformation poses where the auxiliary motors are required to be locked should be selected properly. The design and motion planning concepts are not limited to solving the problems studied in this work. ...
Extending the workspace of cable robots can enhance their motion ability and help us make fuller use of their potential. This work designs a novel cable robot and utilizes cable slackness to extend its workspace. First, we use driving cables actuated by main motors and constrained cables driven by auxiliary motors equipped with lockers to control and restrain the motion of the end-effector respectively. Then we classify the constraints on the end-effector into different modes according to the slackness of different constrained cables whose lengths can be changed by auxiliary motors and use continuous tension distribution to switch among them. To expand the mechanism's workspace, the properties of the constraint mode series are analyzed and the static reachable workspace associated with it is defined, which guarantees the existence of feasible point-to-point trajectories. In particular, tree-based basic and general constraint mode series connection algorithms are designed to connect two targets in the static reachable workspace efficiently considering the necessary condition for the existence of the connection. After that, dual workspaces and subspace-based motion planning algorithms are designed to connect multiple targets in the static reachable workspace of the mechanism, and the quality of the trajectories is improved by using different manipulations of the constraint mode series. Since only driving cables are actuated by servo motors and passively constrained cables are adopted to compensate for the weight of the end-effector, the size of actuators and the energy consumption of the robot are reduced.
... The MACCEPA has been implemented in active lower-limb prostheses [3], exoskeletons [4] and bipedal robots [2]. The integration of locking mechanisms to these systems can result in a substantial upgrade of their performance [5]. ...
... Redundant kinematic DOF can be introduced to reduce the reflected inertia of the drivetrain, in addition to static DOFs, which can be exploited to is used to minimize actuator weight. As such, the operating range of the motor can be reshaped to match the task requirements [5]. ...
public For over three decades, the Brubotics team at Vrije Universiteit Brussel has been at the forefront of human-centric robotics research. Our extensive portfolio encompasses a wide range of innovative approaches designed to enhance the performance, safety, and efficiency of robots across various applications. Through our expertise in developing cutting-edge robotic devices such as exoskeletons, prostheses, and collaborative robots, we have identified a critical issue: conventional engineering design methods often produce systems that are excessively heavy and bulky, resulting in limited productivity, high costs, and significant energy demands. These issues are predominantly linked to the actuation systems. Consequently, our team has concentrated on pioneering advancements in actuation technology to reduce mass and size, lower energy consumption, and improve safety, productivity, and cost-effectiveness. In this extended abstract, we provide a concise overview of our lab's key achievements in this area, both past and present.
... While these metrics summarize important tradeoffs between different technologies, it is important to note that they fail to capture other important characteristics, such as differing control circuitry, additional transmission mechanisms, and diversity of functionality. For additional comparisons, see Plooij et al. (2015) and Guo et al. (2019) Device ...
Highly articulated organisms serve as blueprints for incredibly dexterous mechanisms, but building similarly capable robotic counterparts has been hindered by the difficulties of developing electromechanical actuators with both the high strength and compactness of biological muscle. We develop a stackable electrostatic brake that has comparable specific tension and weight to that of muscles and integrate it into a robotic joint. High degree-of-freedom mechanisms composed of such electrostatic brake enabled joints can then employ established control algorithms to achieve hybrid motor-brake actuated dexterous manipulation. Specifically, our joint design enables a ten degree-of-freedom robot equipped with only one motor to manipulate multiple objects simultaneously. We also show that the use of brakes allows a two-fingered robot to perform in-hand re-positioning of an object 45% more quickly and with 53% lower positioning error than without brakes. Relative to fully actuated robots, robots equipped with such electrostatic brakes will have lower weight, volume, and power consumption yet retain the ability to reach arbitrary joint configurations.
... In robots, latches are used to lock springs and joints [14], and often appear as contacting structures like the robot in [13], or as a hook [15], a CAM [16,17], gear teeth [18][19][20], a clutch [21], or a wedge [22]. The attractive force of magnets can act as a force threshold to trigger the release of a spring [23,24]. ...
Jumping microrobots and insects power their impressive leaps through systems of springs and latches. Using springs and latches, rather than motors or muscles, as actuators to power jumps imposes new challenges on controlling the performance of the jump. In this paper, we show how tuning the motor and spring relative to one another in a torque reversal latch can lead to an ability to control jump output, producing either tuneable (variable) or stereotyped jumps. We developed and utilized a simple mathematical model to explore the underlying design, dynamics, and control of a torque reversal mechanism, provides the opportunity to achieve different outcomes through the interaction between geometry, spring properties, and motor voltage. We relate system design and control parameters to performance to guide the design of torque reversal mechanisms for either variable or stereotyped jump performance. We then build a small 356 mg microrobot and characterize the constituent components (e.g., motor and spring). Through tuning the actuator and spring relative to the geometry of the torque reversal mechanism, we demonstrate that we can achieve jumping microrobots that both jump with different take-off velocities given the actuator input (variable jumping), and those that jump with nearly the same take-off velocity with actuator input (stereotyped jumping). The coupling between spring characteristics and geometry in this system has benefits for resource-limited microrobots, and our work highlights design combinations that have synergistic impacts on output, compared to others that constrain it. This work will guide new design principles for enabling control in resource-limited jumping microrobots.
... To achieve this function, one of the first ideas is to use an active system that can actuate a locking or braking element on the transmission. Many mechanisms exist and are used in robotics [8]. Many manipulator arms use electromagnetic brakes or linear solenoids. ...
The aim of this article is to create a system that enables power transmission non-backdrivability in a hand prosthesis with a single actuator. This system allows the motor to be stopped while maintaining the gripping force to prevent the held object from being dropped. This non-backdrivability allows users, for example, to release muscle contractions while still keeping a tight grip on an object, as well as completely turning off the prosthesis to avoid unintentional commands that could lead to loosening the object. Beyond the functional aspect of non-backdrivability, the physical non-backdrivability of the transmission enables the full power of the motors to be utilized without exceeding their thermal limits. To be effectively used, the non-backdrivable system must be energy efficient. A state-of-the-art analysis of different non-backdrivable mechanisms is conducted, evaluating their functioning and maximum efficiency. A novel system is developed based on an existing principle but with a focus on simplicity of manufacturing and fewer components compared to existing systems. An analysis is conducted to understand the effect of each mechanism parameter, and a dimensioning procedure is derived. A prototype is developed to compare theoretical values with measured values. The obtained results are analyzed and discussed.
