Biosimulant Artifact with Embedded Calcium Alginate Bead Sensor for Robot Impact Safety Testing

This paper presents the design of a disposable biosimulant human tissue artifact system for robot safety testing. It is used to provide a visual indication of potentially severe injuries caused in the case of a robot impact with a human. The fabrication method is described including the design and fabrication of the calcium alginate bead and the embedding procedure of the beads into the biosimulant artifact. The artifact system is tested with a Dynamic Impact Testing and Calibration Instrument (DITCI) from the National Institute of Standards and Technology (NIST). The design is useful for the preparation of new robot safety standards. INTRODUCTION The movement of manufacturing to countries featuring labor with low hourly wages over the last fifteen years has motivated the development of a new generation of industrial robots that can work side-by-side with human workers [1]. This has created a new technology of HumanCollaboration-Robotics (HCR), which combines the intelligence and dexterity of humans with the strength, repeatability, and endurance of industrial robots [2]. Since most robots are powerful moving machines, the safety of workers working around these robots has become a top priority for safety standards development. We are using biological simulant (biosimulant) materials for the fabrication of inexpensive, disposable HCR safety testing artifacts. These testing artifacts will make possible the measurement of forces, pressure, and strain when humans and robots come into contact as well as of the magnitude of injuries caused by robot static and impact pressure. The Dynamic Impact Testing and Calibration Instrument (DITCI) is a simple instrument shown in Figure 1, with a significant data collection and analysis capability that is used for the testing and calibration of biosimulant human tissue artifacts [3, 4]. Various research groups have used human subjects to collect data on pain induced by the clamping force, pressure, and maximum impact force of the HCRs [5, 6, 7, 8]. Although the results of these tests are hard to reproduce and can vary even among subjects of similar characteristics, they can be very useful for the preparation of safety testing standards. Unfortunately, human safety testing is not an option for HCR industrial applications every time there is a change of a tool or control program, so the use of a biosimulant artifact system is expected to be a good alternative. FIGURE 1. Impact testing set up. Much work has been done in the design of pressure sensors. Sander et al. [9] designed a monolithic capacitive sensor. Someya et al. [10] designed a flexible pressure sensor matrix for the application of artificial skin. A number of Microelectro-mechanical Systems (MEMS) designs are proposed for pressure sensors [11, 12, 13, 14]. However, the cost of these pressure sensors is high. Based on a chemical fabrication method, we could build a cheap and disposable measurement system. Daly and Knorr [15] proposed the fabrication of a chitosan alginate capsule. Huguet and Dellacherie [16] described the fabrication of calcium alginate beads coated with chitosan. In this paper, we present a chemical based fabrication procedure for a disposable human artifact embedded with calcium alginate bead for robot impact safety testing. The rest of the paper is organized as follows: We firstly present the design methodology of the artifact system. Secondly, the fabrication method of the calcium alginate bead is followed by a description of the procedure for embedding the beads into the human tissue artifact. Finally, the biosimulant artifact system is mounted on the DITCI for an impact testing. DESIGN OF BIOSIMULANT ARTIFACT WITH EMBEDDED BEAD In this section, we describe the design of the biosimulant artifact system. As shown in Figure 2, the sensor system consists of three parts: top leather, soft tissue, and embedded sensor. The top leather is a piece of artificial skin of disk shape. Soft tissue is made of ballistic gelatin. The embedded sensor is a calcium alginate-based bead design. The combination of top leather and ballistic gelatin is called the biosimulant artifact [3]. The biosimulant artifact simulates human skin and muscle, and simulates the stress distribution when the impact force is applied on the top surface of the skin. The deformation of the ballistic gelatin caused by the dynamic impact force results in the stress distributed on the bead sensors. Thus, the embedded bead sensors will deform corresponding to the deformation of the ballistic gelatin. When the red beads over-deform, they will be destroyed when the impact force causes a certain pressure threshold to be exceeded. Due to the low fabrication costs, the artifact may be disposed of after testing. FABRICATION OF CALCIUM ALGINATE BEAD In this section, we present the fabrication of the calcium alginate bead. The main chemical reacTop leather