Debao Zhou

A real-time optical sensor for simultaneous measurement of three-DOF motions

The need for simultaneous measurement of multiple degree-of-freedom (DOF) motions can be found in numerous applications such as robotic assembly, precision machining, optical tracking, wrist actuators, and active joysticks. Conventional single-axis encoders, though capable of providing high-resolution (linear or angular) measurements, rely on mechanical linkages (that often introduce frictions, backlashes, and singularities) to constrain the device so that the three-DOF (3-DOF) motion can be deduced from the individual orthogonal measurements. We present here a noncontact optical sensor for 3-DOF planar and spherical orientation measurements. We begin with the operational principle of a microscopic-surface-based optical sensor. The design concept and theory of a dual-sensor system capable of measuring 3-DOF planar and spherical motions in real time are then presented. Along with a detailed analysis, the concept feasibility of two prototype 3-DOF dual-sensor systems for measuring the instantaneous center of rotation and the angular displacement of a moving surface is demonstrated experimentally. It is expected that the analysis will serve as a basis for optimizing key design parameters that could significantly influence the sensor performance.

An efficient foot-force distribution algorithm for quadruped walking robots

One of the important issues of walking machine active force control is a successful distribution of the body force to the feet to prevent leg slippage. In this paper, a new force distribution method, the Friction Constraint Method (FriCoM), is introduced. The force distribution during the walking of a typical quadruped crawl gait is analyzed by using the FriCoM. Computation results show that the distributed forces of the feet are continuous during the walking. This reflects the change of the force distribution during actual conditions. The comparison with a pseudo-inverse method shows that the FriCoM is more practical. The FriCom also requires less computation time than that by an incremental optimization method. Some problems, such as the singularity in the application of the FriCoM, are discussed. The FriCoM will be used in the active force control of a quadruped robot that is taken as a platform for the research on the study of terrain adaptation.

A real-time optical sensor for simultaneous measurement of 3-DOF motions

The need for simultaneous measurement of more-than-one degree-of-freedom (DOF) motions can be found in numerous applications such as robotic assembly, precision machining, optical tracking, wrist actuators, and active joysticks. Conventional encoders, though they are able to provide very high-resolution measurements (linear or angular), are limited to single-DOF sensing in motion control. The use of these single-DOF encoders for measuring 3-DOF motions in real time often requires additional mechanical linkages that often introduce frictions and backlashes. We present here a non-contact optical sensor for measuring multi-DOF motions. This paper begins with the operational principle of a microscopic-surface-based optical sensor. The design concept and theory of a dual-sensor system capable of measuring a 3-DOF planar motion in real time is then presented. Along with a detailed analysis, the concept feasibility of a prototype 3-DOF dual-sensor system for measuring the instantaneous center of rotation and the angular displacement of a moving surface is demonstrated experimentally. It is expected that the analysis will serve as a basis for optimizing key design parameters that significantly influence the sensor performance.

Development of a Skin-Like Tactile Sensor Array for Curved Surface

In this paper, we develop a skin-like tactile sensor array to measure the contact pressure of curved surfaces. The sensor array is laminated into a thin film 3 mm in thickness and can easily be wrapped around a pencil without damaging its skin-like structure. So far, we have achieved the array containing 8 × 16 sensor elements. Its spatial resolution is 1 element per 9 mm2 area and it can measure the pressure up to 360 kPa. The sensor-array patch contains three layers. The upper and lower layers are polydimethylsiloxane (PDMS) thin films embedded with the conductor strips formed by PDMS-based silver nanowires (AgNWs) networks. The middle layer is formed by the mixing of nickel powder with liquid PDMS for contact force measurement. Experimental tests have demonstrated that conductor strips on the upper layer can maintain their resistances ~ 23 Ω with increase when the tensile strain is up to 50%. Noted is the conductor made with carbon nanotubes can keep its conductivity unchanged for up to only 40% tensile strain. Through fatigue tests, it is observed that the measured AgNWs/PDMS conductor strip exhibits low and stable resistances. This is one of the most desired behaviors of the stretchable interconnects for signal transmission. The integrated sensor system can successfully measure the contact pressure induced by objects of different shapes. It can be applied on curved or non-planar surfaces in robots or medical devices for force detection and feedback.

A spherical encoder for real-time measurements of three-DOF wrist orientations

The need for simultaneous measurement of more-than-one degrees-of-freedom (DOF) motions of an object can be found in numerous applications such as robotic assembly, precision machining, optical tracking, wrist actuators, and active joysticks. Conventional single-axis encoders, though capable of providing high-resolution linear or angular measurements, require additional mechanical linkages that often introduce frictions, backlashes, and singularities. In this paper, a non-contact optical sensor for three-DOF orientation measurement is present. Unlike other contemporary designs, which often require a specific pattern to be drawn on a surface, this optical sensor presented here relies only on microscope features on natural surfaces to detect incremental motions. Here we offer a detailed description of the design and the development of a dual-sensor system capable of measuring three-DOF motions in real time. The analysis that is essential for optimizing the sensor design has been validated experimentally.

Cutting, 'by pressing and slicing', applied to the robotic cut of bio-materials. II. Force during slicing and pressing cuts

The applications of robotics are becoming more and more common in non-traditional industries such as the medical industry including robotic surgery and sample microtoming as well as food industry that include the processing of meats, fruits and vegetables. In this paper, the influence of the blade edge-shape and its slicing angle on the cutting of biomaterials are formulated and discussed based on the stress analysis that has been presented in part I. Through modeling the cutting force, an optimal slicing angle can be formulated to maximize the feed rate while minimizing the cutting forces. Moreover, the method offers a means to predict cutting forces between the blade and the biomaterials, and a basis for design of robust force control algorithms for automating the cutting of biomaterials

Tracking-based deer vehicle collision detection using thermal imaging

Deer vehicle collision (DVC) is constantly a major safety issue for the driving on rural road. It is estimated that there are over 35,000 DVCs yearly in the US resulting in about 200 deaths and close to 4,000 reported property damages of one thousand dollars or more. This justifies many attempts trying to detect deer on road. However, very little success has been achieved. In order to reduce the number of DVCs, this work focused on the study of using an infrared thermal camera with tracking system to detect the presence of deer to avoid DVCs. The prototype consists of an infrared thermal temperature image grabbing and processing system, which includes an infrared thermal camera, a frame grabber, an image processing system and a motion tracking system, which includes two motors with their motion control system. By analyzing the infrared thermal images which are independent of visible light, the presence of an animal can be determined in either night or day time through pattern recognition and matching.

Combined use of ground learning model and active compliance to the motion control of walking robotic legs

The foot force/position adjustment method, the hybrid ground-learning model and active compliance force control method (or hybrid GLAC method), is introduced. The proposed method combines the active compliance force control with a ground-learning model for controlling the leg motion of the robot. The ground model reflects the relationship between the leg-end force and the sinkage. To verify the control quality of the proposed method together with the active compliance (AC) control and ground learning model control, experiments based on a robotic leg have been carried out on hard and soft terrain, respectively. The results show that the proposed method can ensure the actual leg-end force to follow closely the changing of reference forces both on hard and soft terrain. Therefore, by using the hybrid GLAC control, the error of the actual forces relative to the reference forces can be reduced more quickly than by using the AC method alone.

A stability analysis of walking robots based on leg-end supporting moments

An essential consideration in the development of any motion planning method for a multilegged vehicle is to maintain stability during walking. We propose a leg-end supporting moment (LSM) method, to measure the stability margin of walking robots. The LSM is defined as the product of the force acting on a supporting leg and the distance between the supporting leg and the opposite edge of the support polygon. These forces and distances can be obtained online from the internal robot sensors. The stability margin evaluated by the LSM method, expressed as LSM/sub m/, is defined as the quotient of the leg-end supporting moment over the weight of the robot. If the LSM/sub m/ is greater than zero, the robot is in stable state. Otherwise the robot will be in marginally stable state or will lose its stability. The simulation results show that the LSM method is suitable for the stability analysis in cases with and without external forces acting on the body. The method is not only effective for flat terrain, but also for uneven terrain. These characteristics enable the LSM method to measure the stability margin of a walking robot in the case of drilling, dragging and manipulating, also in the case when the robot is used in forestry.

Development of a Stretchable Conductor Array With Embedded Metal Nanowires

In this paper, we presented the design, fabrication, and testing of a new type of stretchable conductor array with embedded nanowires. The conductor array could serve as the interconnect for skin-like, conformal circuits, which is one of the key components in a stretchable tactile sensor for minimally invasive surgery (MIS) devices and robots to measure the contact force, where both stretchability and conductivity are required. One example of such applications is to measure the contact force between a colonoscope and the colonic wall during colonoscopy. The proposed conductor array was fabricated by embedding several parallel silver-nanowires (AgNWs) strips (one strip is in the dimension of 3 mm wide, 360 mm long, and less than 0.01 mm thick) into the surface of a polydimethylsiloxane (PDMS) thin film (50 mm wide, 360 mm long 1 mm thick). The conductor array was then wrapped around the surface of a colonoscope for bending tests. The results from the bending tests have demonstrated that the conductor strip has a stable resistance (around 50 Ω) when the bending radius changes from 150 to 25 mm. Multitime bending tests have shown no conductivity change. Moreover, wiping tests have shown that the AgNWs/PDMS conductor array could survive external damage from its working environment. With the good repeatability and unchanged conductivity during stretching, the conductor array developed in this paper is applicable to a stretchable tactile sensor.