Relational algebra provides a theoretical foundation for how modern database management systems optimize and execute queries. Its main concepts are based on set theory and first order logic, which can be challenging for students to learn due to their abstract nature. This paper presents Bags, a new type of visual programming environment (inspired by Snap!) for the teaching of relational operations and data analysis. Students formulate algebraic queries by snapping together graphical blocks that represent data sets and relational operators, resulting in an interactive visualization of the underlying concepts. The outcomes of this work will not only enhance university-level database courses, but also provide an engaging computational thinking resource for K-12 teachers in content areas outside of science and engineering.

This paper describes the algorithm development and experimental results of a vision-guided multiprobe microassembly system. The key focus is to develop the capabilities required for the construction of 3-D structures using only planar microfabricated parts. Instead of using grippers, multiple sharp-tipped probes are coordinated to manipulate parts by using vision feedback. This novel probe-based approach offers both stable part grasping and dexterous part manipulation. The light weight of the part and relatively slow motion means that only kinematics-based control is required. However, probe motions need to be carefully coordinated to ensure reliable and repeatable part grasping and manipulation. Machine vision with multiple cameras is used to guide the motion. No contact force sensor is used; instead, vision sensing of the probe bending is used for the grasp force control. By combining preplanned manipulation sequences and vision-based manipulation, repeatable spatial (in contrast with planar) manipulation and insertion of a submillimeter part have been demonstrated with an experimental testbed consisting of two actuated probes, a passive probe, an actuated die stage, and two cameras for vision feedback.

This paper describes the operator assisted automated assembly of a 3-legged spatial platform by using a vision guided multi-probe assembly process. This is the first step towards the ultimate goal of building a microscale active spatial platform. Two issues are highlighted in this paper: contact management and vision feedback. Using multiple probes for part grasping and manipulation has the advantage of robustness and versatility as compared to micro-grippers. However, the contacts between the probes and the part need to be carefully managed to ensure a grasp that is stable for part pick-up and yet manipulable to allow part motion in a controlled fashion. By using vision guidance, the probes can be coordinated to grasp the parts and lift them off the die securely and reliably. We show that the contacts act as point contacts with friction, so when a part is pressed against a stationary probe, the part rotates about the axis between the contacts, changing its orientation so it may be inserted into a slot in the substrate. We have demonstrated that the three legs can be assembled in a fully automated fashion via multiple-camera vision feedback. The platform is at present assembled via tele-operation. The assembled microstructure measures 450 µm×600 µm. We are now working on the full automation of the assembly onto a substrate populated with MEMS actuators.

Flexure joints are frequently used in precision-motion stages and microrobotic mechanisms due to their monolithic construction. The joint compliance, however, can affect the static and dynamic performance of the overall mechanism. In this paper, we consider the analysis and design of general platform-type parallel mechanisms containing flexure joints. Based on static performance measures such as task-space stiffness and manipulability, and constraints such as joint stress, mechanism size, and workspace volume, we pose the design problem as a multiobjective optimization. We first calculate the Pareto frontier, which can then be used to select the desired design parameters based on secondary criteria, such as performance sensitivity and dynamic characteristics. To facilitate design iteration, we apply the pseudo rigid-body approach with a lumped approximation of the flexure joints. A planar mechanism is used to illustrate the analysis and design techniques.

Flexure joints are frequently used in precision motion stages and micro-robotic mechanisms due to their monolithic construction. The joint compliance, however, can affect the static and dynamic performance of the overall mechanism. In this paper, we consider the analysis and design of general platform type parallel mechanisms containing flexure joints. We consider static performance measures such as task space stiffness and manipulability, while subject to constraints such as joint stress, mechanism size, workspace volume, and dynamic characteristics. Based on these performance measures and constraints, we adopt the multi-objective optimization approach. We first obtain the Pareto frontier, which can then be used to select the desired design parameters based on secondary criteria such as performance sensitivity. To simplify presentation, we consider only lumped approximation of flexure joints in the pseudo-rigid-body approach. A planar mechanism is included to illustrate the analysis and design techniques. Tools presented in this paper can also be applied to a broader class of compliant mechanisms, including robots with inherent joint flexibility as well as compliant robots for contact tasks.

Cable array robots are a class of robotic mechanisms which utilize multiple actuated cables to manipulate objects. This paper discusses the defining characteristics and the important issues relating to this class of robots. One particular type of cable array robot with three cables is presented in detail including kinematic relations and dynamic modeling. The resulting models are used to design a sliding mode control system for the robot, providing robustness to uncertainty in the mass of manipulated objects while tracking a given trajectory. Experimental results are provided for the system, showing that the robot is capable of tracking a trajectory within several centimeters, which is reasonable performance for many industrial applications. These results are discussed in detail and future research plans are presented.

A multiple cable robotic crane designed to provide improved cargo handling is investigated. The equations of motion are derived for the cargo and flexible cables using Lagrange's equations and the assumed modes method. The resulting equations are kinematically redundant due to fewer degrees of freedom of the cargo than the number of cables. A nonlinear transformation is used to reduce the number of variables. An optimal force distribution method is then applied to the equations to solve for a set of necessary cable tensions which will cause the system to track a desired trajectory. These tensions are tested on the dynamic model using computer simulation. The results are compared against desired cable lengths and results gained in previous research using a rigid cable model.

Offshore loading and unloading of cargo vessels and on board cargo relocation during conditions of Sea State 3 or greater have been found to be difficult with existing crane technology due to oscillation of the payload. A new type of crane which uses four actuated cables to control the motion of the payload is presented. The closed chain configuration will intuitively provide more stability with respect to the motion of the sea compared to existing cranes. The kinematics and dynamics are derived using cable coordinates. Since there are four cables and three degrees of freedom, the system is redundant. This problem is solved by applying a geometric constraint to the equations of motion such that the reduced number of equations equals the degrees of freedom. The force distribution method is applied using linear programming to solve for the required cable tensions. Simulation results showing cable tensions and cable lengths during a typical crane operation are presented.