CS223A - Introduction to Robotics-lecture14
Topics: PD Control, Control Partitioning, Motion Control, Disturbance Rejection, Steady-State Error, PID Control, Effective Inertia Instructor (Oussama Khatib):Okay. Okay. Let’s get started. So today’s video segment is about tactile sensing. Now, I wonder what is difficult about building tactile sensors; anyone has an idea? So what is the problem with building a tactile sensor? Oh, you used to see the video first, okay. So, yeah. Student:Do you need functions to be able to, I mean, do you need a perturbation to be able to see what you’re touching sometimes? Instructor (Oussama Khatib):Well, yeah, sometimes you, I mean, a human – tactile sensing is amazing. So you have the static information, so if you grab something, now the whole surface is in contact, and you can determine the shape, right? So what does it mean in term of, like, designing a tactile sensor, just if you think about the static case? Student:It’s soft, malleable. Instructor (Oussama Khatib):Well, you need some softness in the thing you are putting. Then you need to take this whole information, what kind of resolution do you need, if you are touching to feel the edge? You need a lot of pixels, right? So how can you take this information and – first of all, how you determine that information; what kind of procedure do you – yes? Student:Well, there’s an element of pressure, like, how hard you’re – the average – how are you touching on all these different things. Instructor (Oussama Khatib):Okay. So you can imagine, maybe, a sort of resistive or capacitive sensor that will deflect a little bit and give you that information. How many of those you would need? You need, sort of, an array, right? So how large, like, let’s say this is the end of factor. I’m trying to see if you did that problem – you’re going to have a lot of information here, and you need to take it back, and you have a lot of wires; you have a matrix, and you’re going to have a lot of, basically, information to transmit. So, the design of tactile sensors being this problem of how we can put enough sensors, and how we can extract this information and take it back. So these guys came up with an interesting idea; here it is. The light, please. [Video]: A novel tactile sensor using optical phenomenon was developed. In the tactile sensors shown here, light is injected at the edge of an optical wave guide made of transparent material and covered by an elastic rubber cover. There is clearance between the cover and the wave guide. The injected light maintains total internal reflection at the surface of the wave guide and is enclosed within it. When an object makes contact with it, the rubber cover depresses and touches the wave guide. Scattered light arises at the point of contact due to the change of the reflection condition. Such tactile information can be converted into a visual image. Using this principle, a prototype finger-shaped tactile sensor with a hemispherical surface was developed. A CCD camera is installed inside the wave guide to detect scattered light arising at the contact location on the sensor’s surface. The image from the CCD camera is sent to the computer, and the location of the scattered light is determined by the image processing software. Using this information, the object’s point of contact on the sensor’s surface can be calculated. To improve the size and the operational speed of the sensor, a miniaturized version was developed. The hemispherical wave guide with cover, the light source infrared LED’s, a position-sensitive detector for converting the location of the optical input into an electric signal, and the amplifier circuit were integrated in the sensor body. The scattered light arising at the point of contact is transmitted to the detector through a bundle of optical fibers. By processing the detector’s electric signal by computer, it is possible to determine the contact location on the sensor’s surface in 1.5 milliseconds. Through further miniaturization, a fingertip diameter of 20 millimeters has been achieved in the latest version of the tactile sensor. It is currently planned to install this tactile sensor in a robotic hand with the aim of improving its dexterity. Instructor (Oussama Khatib):Okay. A cool idea, right? Because now you’re taking this information, and taking it into a visual image, and transmitting the image, and, in fact, this was done a long time ago. I believe the emperor of Japan was visiting that laboratory, and he saw this, and he was quite impressed. Before starting the lecture, just wanted to remind you that we are going to have two review sessions on Tuesday and Wednesday next week, and we will, again, sign up for two groups. I hope we will have a balance between those who are coming on Tuesday and Wednesday. We will do the signing up next Monday, so those who are not here today, be sure to come on Monday to sign up, all right? Okay. Last lecture we discussed t
Topics: PD Control, Control Partitioning, Motion Control, Disturbance Rejection, Steady-State Error, PID Control, Effective Inertia Instructor (Oussama Khatib):Okay. Okay. Let’s get started. So today’s video segment is about tactile sensing. Now, I wonder what is difficult about building tactile sensors; anyone has an idea? So what is the problem with building a tactile sensor? Oh, you used to see the video first, okay. So, yeah. Student:Do you need functions to be able to, I mean, do you need a perturbation to be able to see what you’re touching sometimes? Instructor (Oussama Khatib):Well, yeah, sometimes you, I mean, a human – tactile sensing is amazing. So you have the static information, so if you grab something, now the whole surface is in contact, and you can determine the shape, right? So what does it mean in term of, like, designing a tactile sensor, just if you think about the static case? Student:It’s soft, malleable. Instructor (Oussama Khatib):Well, you need some softness in the thing you are putting. Then you need to take this whole information, what kind of resolution do you need, if you are touching to feel the edge? You need a lot of pixels, right? So how can you take this information and – first of all, how you determine that information; what kind of procedure do you – yes? Student:Well, there’s an element of pressure, like, how hard you’re – the average – how are you touching on all these different things. Instructor (Oussama Khatib):Okay. So you can imagine, maybe, a sort of resistive or capacitive sensor that will deflect a little bit and give you that information. How many of those you would need? You need, sort of, an array, right? So how large, like, let’s say this is the end of factor. I’m trying to see if you did that problem – you’re going to have a lot of information here, and you need to take it back, and you have a lot of wires; you have a matrix, and you’re going to have a lot of, basically, information to transmit. So, the design of tactile sensors being this problem of how we can put enough sensors, and how we can extract this information and take it back. So these guys came up with an interesting idea; here it is. The light, please. [Video]: A novel tactile sensor using optical phenomenon was developed. In the tactile sensors shown here, light is injected at the edge of an optical wave guide made of transparent material and covered by an elastic rubber cover. There is clearance between the cover and the wave guide. The injected light maintains total internal reflection at the surface of the wave guide and is enclosed within it. When an object makes contact with it, the rubber cover depresses and touches the wave guide. Scattered light arises at the point of contact due to the change of the reflection condition. Such tactile information can be converted into a visual image. Using this principle, a prototype finger-shaped tactile sensor with a hemispherical surface was developed. A CCD camera is installed inside the wave guide to detect scattered light arising at the contact location on the sensor’s surface. The image from the CCD camera is sent to the computer, and the location of the scattered light is determined by the image processing software. Using this information, the object’s point of contact on the sensor’s surface can be calculated. To improve the size and the operational speed of the sensor, a miniaturized version was developed. The hemispherical wave guide with cover, the light source infrared LED’s, a position-sensitive detector for converting the location of the optical input into an electric signal, and the amplifier circuit were integrated in the sensor body. The scattered light arising at the point of contact is transmitted to the detector through a bundle of optical fibers. By processing the detector’s electric signal by computer, it is possible to determine the contact location on the sensor’s surface in 1.5 milliseconds. Through further miniaturization, a fingertip diameter of 20 millimeters has been achieved in the latest version of the tactile sensor. It is currently planned to install this tactile sensor in a robotic hand with the aim of improving its dexterity. Instructor (Oussama Khatib):Okay. A cool idea, right? Because now you’re taking this information, and taking it into a visual image, and transmitting the image, and, in fact, this was done a long time ago. I believe the emperor of Japan was visiting that laboratory, and he saw this, and he was quite impressed. Before starting the lecture, just wanted to remind you that we are going to have two review sessions on Tuesday and Wednesday next week, and we will, again, sign up for two groups. I hope we will have a balance between those who are coming on Tuesday and Wednesday. We will do the signing up next Monday, so those who are not here today, be sure to come on Monday to sign up, all right? Okay. Last lecture we discussed t