An official website of the United States government
There are many ways for a gripper to estimate the forces between its fingers. If powered by direct-drive brushless motors, then one technique is to measure their current. This is not the most accurate technique, but it is simple, keeps the sensor remote, and requires no new components. The estimation involves multiplying current signals through by the torque constant and the inverse transpose of the Jacobian. The Jacobian either amplifies the signal from fingertip force to motor current (at the cost of tip force production), or diminishes it (with the gain of tip force production), indicating an inherent trade-off. However, the Jacobian is a function of configuration, and for any workspace point there are multiple configurations (multiple inverse kinematics solutions), therefore a selection of Jacobian exists. For a given workspace point, the number of Jacobian choices is just a few, but these choices can be designed (through dimensional synthesis) to overcome the trade-off. The problem can be framed as velocity ellipse synthesis over multiple output modes. In this work, we conduct optimal synthesis to compute a new gripper design. The gripper was built and tested. It transitions between two different modes: sense mode and grip mode. Sense mode can sense forces 3 times smaller than grip mode. Grip mode can exert forces 4 times greater than sense mode.
more »
« less
Photo-induced force microscopy (PiFM) – principles and implementations
Photo-induced force microscopy (PiFM) is a scan probe technique that offers images with spectroscopic contrast at a spatial resolution in the nanometer range. PiFM utilizes the non-propagating, enhanced near field at the apex of a sharp tip to locally induce a polarization in the sample, which in turn produces an additional force acting on the cantilevered tip. This photo-induced force, though in the pN range or less, can be extracted from the oscillation properties of the cantilever, thus enabling the generation of photo-induced force maps. Since its inception in 2010, the PiFM technique has grown into a useful nano-spectrocopic tool that has expanded its reach in terms of imaging capabilities and applications. In this review, we present various technical implementations of the PiFM approach. In addition, we discuss the physical origin of the PiFM signal, highlighting the contributions from dipole–dipole forces as well as forces that derive from photo-thermal processes.
more »
« less
- Award ID(s):
- 1905582
- PAR ID:
- 10347637
- Date Published:
- Journal Name:
- Chemical Society Reviews
- Volume:
- 51
- Issue:
- 11
- ISSN:
- 0306-0012
- Page Range / eLocation ID:
- 4208 to 4222
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
There is considerable interest in measuring, with nanoscale spatial resolution, the physical properties of lipid membranes because of their role in the physiology of living systems. Due to its ability to nondestructively image surfaces in solution, tapping mode atomic force microscopy (TMAFM) has proven to be a useful technique for imaging lipid membranes. However, further information concerning the mechanical properties of surfaces is contained within the time-resolved tip/sample force interactions. The tapping forces can be recovered by taking the second derivative of the cantilever deflection signal and scaling by the effective mass of the cantilever; this technique is referred to as scanning probe acceleration microscopy. Herein, we describe how the maximum and minimum tapping forces change with surface mechanical properties. Furthermore, we demonstrate how these changes can be used to measure mechanical changes in lipid membranes containing cholesterol.more » « less
-
Abstract Soft tissue biopsy is a necessary diagnostic and therapeutic procedure, but traditional biopsy needles can cause harm to the patient, including tissue damage, bleeding, and pain. These can compromise the accuracy of the sample and negatively impact the patient’s well-being. Hence, there has been a growing interest in developing bio-inspired surgical needles that are safer, more effective, and more comfortable for the patient. The scorpion-inspired curved tip needle study focuses on analyzing the mechanics of needle-tissue interaction and creating needles that travel through soft tissue with minimum resistance at the tip. An essential aspect of the study is the mechanics and geometry of the needle tip, which plays a crucial role in its performance. The study incorporates structures of curved scorpion’s stinger to balance between penetration and minimal needle-tissue interaction forces. In this study, various parameters of curved tip geometry are explored to decrease the insertion and extraction forces. Tests are initially performed on brain tissue mimicking medical gelatin with Young’s modulus of 2kPa. It is observed that the insertion force with curved tip needles is decreased by up to 21.7%, and the extraction force is decreased by up to 28.2%. This study shows that a scorpion-inspired tip design can minimize insertion and extraction forces, leading to less tissue damage and deformation. Furthermore, the proposed tip design has great potential to improve surgical needles for more effective minimally invasive percutaneous procedures with various applications such as biopsy, brachytherapy, tumor ablation, and drug delivery to the brain.more » « less
-
Abstract Atomic force microscope (AFM)-based nanolithography is a cost-effective nanopatterning technique that can fabricate nanostructures with arbitrary shapes. However, existing AFM-based nanopatterning approaches have limitations in the patterning resolution and efficiency. Minimum feature size and machining performance in the mechanical force-induced nanofabrication process are limited by the radius and sharpness of the AFM tip. Electric-field-assisted atomic force microscope (E-AFM) nanolithography can fabricate nanopatterns with features smaller than the tip radius, but it is very challenging to find the appropriate input parameter window. The tip bias range in E-AFM process is typically very small and varies for each AFM tip due to the variations in tip geometry, tip end diameter, and tip conductive coating thickness. This paper demonstrates a novel electric-field and mechanical vibration-assisted AFM-based nanofabrication approach, which enables high-resolution (sub-10 nm toward sub-5 nm) and high-efficiency nanopatterning processes. The integration of in-plane vibration with the electric field increases the patterning speed, broadens the selectable ranges of applied voltages, and reduces the minimum tip bias required for nanopatterning as compared with E-AFM process, which significantly increases the versatility and capability of AFM-based nanopatterning and effectively avoids the tip damage.more » « less
-
Acoustic levitation is frequently used for non-contact manipulation of objects and to study the impact of microgravity on physical and biological processes. While the force field produced by sound pressure lifts particles against gravity (primary acoustic force), multiple levitating objects in the same acoustic cavity interact via forces that arise from scattered sound (secondary acoustic forces). Current experimental techniques for obtaining these force fields are not well-suited for mapping the primary force field at high spatial resolution and cannot directly measure the secondary scattering force. Here, we introduce a method that can measure both acoustic forces in situ, including secondary forces in the near-field limit between arbitrarily shaped, closely spaced objects. Operating similarly to an atomic force microscope, the method inserts into the acoustic cavity a suitably shaped probe tip at the end of a long, flexible cantilever and optically detects its deflection. This makes it possible to measure forces with a resolution better than 50 nN and also to apply stress or strain in a controlled manner to manipulate levitated objects. We demonstrate this by extracting the acoustic potential present in a levitation cavity, directly measuring the acoustic scattering force between two objects, and applying tension to a levitated granular raft of acoustically bound particles in order to obtain the force–displacement curve for its deformation.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/D2CS00052K
