State Of The Art Robotic Grippers And Applications

Abstract:In this paper, we present a recent survey on robotic grippers. In many cases, modern grippers outperform their older counterparts which are now stronger, more repeatable, and faster. Technological advancements have also attributed to the development of gripping various objects. This includes soft fabrics, microelectromechanical systems, and synthetic sheets. In addition, newer materials are being used to improve functionality of grippers, which include piezoelectric, shape memory alloys, smart fluids, carbon fiber, and many more. This paper covers the very first robotic gripper to the newest developments in grasping methods. Unlike other survey papers, we focus on the applications of robotic grippers in industrial, medical, for fragile objects and soft fabrics grippers. We report on new advancements on grasping mechanisms and discuss their behavior for different purposes. Finally, we present the future trends of grippers in terms of flexibility and performance and their vital applications in emerging areas of robotic surgery, industrial assembly, space exploration, and micromanipulation. These advancements will provide a future outlook on the new trends in robotic grippers.Keywords: robotic grippers; grasping; end effector; micromanipulators; robots

State of the Art Robotic Grippers and Applications

We survey the state of the art in a variety of force sensors for designing and application of robotic hand. Most of the force sensors are examined based on tactile sensing. For a decade, many papers have widely discussed various sensor technologies and transducer methods which are based on microelectromechanical system (MEMS) and silicon used for improving the accuracy and performance measurement of tactile sensing capabilities especially for robotic hand applications. We found that transducers and materials such as piezoresistive and polymer, respectively, are used in order to improve the sensing sensitivity for grasping mechanisms in future. This predicted growth in such applications will explode into high risk tasks which requires very precise purposes. It shows considerable potential and significant levels of research attention.

In this paper, the different techniques for measuring force or interface pressures are presented. These techniques include load cells, pressure indicating film, and tactile pressure system. Similarly, a review on industry pressure sensing that involves the pick and place applications and algorithm control is also highlighted. The paper also discusses the MEMS sensor technology and different types of sensors while the last section of this part discusses the piezoresistive flexiForce sensor. FlexiForce sensor has a good substrate material, which is a polymer that enhances the force sensing and improves the performance of force, linearity, hysteresis, drift, and temperature sensitivity compared to any other thin film. Furthermore, it is flexible and ultrathin enough as the researchers and designers can use it in different integrated applications as well as for applications that are oriented to manipulative tasks with grippers of robotic hand. In a nutshell, new applications for tactile pressure sensing show a high increase in publications and research attention as viewed in Table 2. As a result, the design of sensor becomes more precise with higher reliability to overcome the problems.

Load cell is a type of pressure sensor, which is commonly used in industrial weighing product to measure force such as goods and vehicles. The gripper of a robotic hand that picks up an object can be equipped with load cells in order to provide compression force feedback to the control system which prevents damage to the object or released too early. Also, load cells can be used to measure the compression forces during a robot walk to provide data for the equilibrium-controlling system. In industrial machinery, rods, beams, wheels, and bars are instrumented in order to control the forces exerted on them. Due to this variety of possible applications, load cells are very important [23]. There are many types of technologies which are used to measure loads such as strain gauges, piezoelectric elements, and variable capacitance.

From the reviews that have been obtained, there are several factors to be considered, specifically on technology for interface force and pressure measurement between two surfaces for robotic hand applications purposes. Comparisonwise, load cells provide the most reliable data pressure measurement, but the size and number of load cells limit the density of measurement points. The total load can be easily reported; however, the size of the load cell can be a limiting factor when it reaches fine granularity due to its pressure distribution.

Pressure indicating film can be used in variety of applications such as robotic hand, but the nature of the film will only provide the peak pressure between interfaces during a measurement. This has obvious limitations when trying to measure dynamic applications and also the resulting data pressure measurement has less accuracy, whereas tactile pressure sensor can provide detailed dynamic measurements of interface pressure with minimal impact on system dynamics. The sensing elements need to be properly calibrated to provide accurate data, but the resulting measurements will provide the most in-depth analysis of interface system dynamics. Depending on the information needed and the physical constraints of the system being measured, load cells, pressure indicating film, and tactile pressure sensors each have advantages and constraints for providing accurate and meaningful data pressure measurement. Understanding how these strengths and limitations influence an application is crucial.

The force sensing resistor (FSR) is based on piezoresistive sensing technology. It can be made in a variety of shapes and sizes and can be utilized in many applications in order to measure a proportional change in force and rate of change and also detects contact or touch between objects. FlexiForce manufactured Tekscan is one of the most piezoresistive sensors widely used in robotic hand. Figure 7 shows a tactile force sensor or FlexiForce sensors. This sensor is considered one of the best ideal force sensors for designers, researchers, or anyone who needs to measure forces. With its thin construction, flexibility, and force measurement ability, the FlexiForce sensor can measure the force between any two surfaces and is resilient to most environments. FlexiForce has better force sensing properties, linearity, low hysteresis, drift, and temperature sensitivity than any other thin film force sensors according to the good substrate material which is a polymer. This material has been considered suitable enough to use in robotic hand for grasping objects effectively.

The structure of the force sensor is a substitute of a matrix of sensing traces; the ink uniformly covers an area to measure the total force applied to that space. The sensor consists of two layers of substrate as shown in Figure 7. This substrate is formed of polyester film and a conductive material, silver, which applies to each layer. Layer of pressure sensitive ink is then used, followed by adhesive to combine the two layers of substrate together to compose the sensor. Additionally, the FlexiForce sensor decreases the resistance of the sensing element when the force applied increases. In this context, various applications using FlexiForce sensor are implemented by many researchers [39]. As an example, measurement of interface pressure or force between two soft objects is presented in [40]. Teleoperated robotic systems using tactile force sensor for the design and development of a low cost control rig to intuitively manipulate an anthropomorphic robotic arm with gripping force sensing are reported in [41]. The measurement of low interface pressure between the skin support surfaces and pressure garments is also discussed in [42]. Thereupon, one good example of using FlexiForce sensors is pick and place application which offers to achieve high sensitivity and minimize slip movement and weight measurement with a secure grasp.

In this context, manipulation capabilities are one of the robotic hand applications that are central to a robot system. Figure 10 shows an example using commercial products, a robotic hand with tactile sensors from Pressure Profile Systems, Inc. (PPS). This tactile sensing technology gives the robotic hand the ability to manipulate delicate objects without breaking them. Moreover, they will also be able to operate at optimized low powers for energy efficiency by using minimized grasp force. Robotic platform using capacitive sensors is also produced by Pressure Profile Systems, Inc., and it is described in [63].

From recent development, it is traced that manipulation control is important for a robot. Manipulation control requires some kind of feedback which could provide information about the interaction between the gripper and the grasp objects. This feedback information can be used to implement an algorithm control to achieve the function operator of any robotic hand application as required. It has also been reported that multifingered robotic hand executes particular tasks of grasping an object, which needs to control the measuring required forces for successful operation and dexterous gripper. In addition, it can grasp various objects by changing its shape. Nonetheless, in many cases they lack linearity or sensitivity, especially, in terms of masterful gripper [74]. The robotic hand gripper can increase the sensitivity as well as linearity by using an intelligent feedback control which will be doing the mechanism of gripper object effectively. To wrap up everything, various robotic hand applications using the different algorithm control had been discussed based on tactile sensing capabilities to increase accuracy, flexibility, and receptivity. Moreover, in future robotic hand applications, the manipulators will have to be made lighter and move faster with higher accuracy and work independently. For instance, the automation of complex tasks in industrial applications would be highly enhanced if robots could operate at high speed with high accuracy. Nevertheless, the current robot designs are made massive in size in order to increase rigidity; thereupon, these aims cannot be executed. To achieve high speed operation and faster response for robotic hands manipulations, we should reduce the driving torque requirement. For this purpose, many one-arm flexible robot arms have been built in laboratories [75, 76]. The Shadow Dextrous Robot Hand, in Figure 12, is an advanced humanoid robot hand system available for purchase and is regarded as one of the most advanced robot hands in the current world. 041b061a72