Conventionally, a cable driven parallel mechanism (CDPM) pose is obtained through the forward kinematics from measurements of the cable lengths. However, this estimation method can be limiting for some applications requiring more precision. This paper proposes to use cable angle position sensors in addition to cable length measurements in order to improve the accuracy of such mechanisms. The robot pose is first obtained individually by the cable length measurements and the cable angle position measurements. A data fusion scheme combining these two types of measurements is then proposed in order to improve the CPDM accuracy. Finally, simulations and experiments are presented in order to assess the benefits of using cable angle position sensors on the CDPM.

This paper presents a methodology to analyze the assembly conditions of parallel manipulators and compute the maximum pose errors of their moving platform, while considering geometric errors, joint clearances, link flexibility and joint elasticity. First, the proposed methodology consists in determining the zone(s) of the manipulator workspace in which the manipulator can be assembled assuming that its links and joints are rigid, while taking into account geometric errors and joint clearances. Then, the minimum energy required to assemble the manipulator in the non-assembly zone(s) is computed, while considering link flexibility and joint elasticity. The maximum pose errors of the moving-platform are also computed throughout the manipulator workspace. Finally, a two-dof spatial parallel manipulator, named IRSbot-2, is used as an illustrative example.

This paper presents a cable-driven parallel mechanism as a haptic interface and its underlying control method. This human-sized, three-degree-of-freedom mechanism has a tetrahedral architecture, four cables and evolves in three-dimensional space. A brief review of the kinematics of the mechanism is presented. Also, an admittance control law coupled with a closed-loop velocity controller is proposed. The control method is then refined by introducing adaptations for smooth surfaces and sharp edges. This control method is then validated by experimental results. Furthermore, the geometry of the mechanism is identified by a method that does not require any other sensor than the motor encoders.

Interest in low-cost force-torque sensors with high performance will continue to increase in the next years, as robot control needs to rely on more sensors to move into the human environment. Existing force-torque sensors still suffer from some shortcomings such as noise sensitivity, low resolution and high cost. This limits their use in some emerging applications. Through an advanced systematic design method based on a symbolic formulation of the wrench-displacement relationship, we designed compact and cost-effective three-axis capacitance-based force sensor. Despite its relative simplicity, our sensor exhibits a very good sensitivity thanks to the electronic components selected, but also to a special soft silicone layer filled with nanoparticles of ferroelectric ceramic. This composite we made has a relatively high dielectric constant. This paper presents the design process that led to the sensor including the structure, the capacitance measurement circuit and the fabrication of the soft dielectric. Characterization tests have also been carried out on a prototype of the sensor and the results show that it is sensitive and easy to fabricate.

Numerous performance indices have been proposed to compare robot architectures based on their kinematic properties. However, none of these indices seems to draw a consensus among the robotics community. The most notorious indices, which are manipulability and dexterity, still entail some drawbacks, which are mainly due to the impossibility to define a single invariant metric for the special Euclidean group. The natural consequence is to use two distinct metrics, i.e., one for rotations and one for point displacements, as has already been proposed by other researchers. This is the approach used in this paper, where we define the maximum rotation sensitivity and the maximum point-displacement sensitivity. These two indices provide tight upper bounds to the end-effector rotation and point-displacement sensitivity under a unit-magnitude array of actuated-joint displacements. Therefore, their meaning is thought to be clear and definite to the designer of a robotic manipulator. Furthermore, methods for the computation of the proposed indices are devised, some of their properties are established and interpreted in the context of robotic manipulator design, and an example is provided.

Several triaxial accelerometers are known. However, to the knowledge of the authors, no true, triaxial accelerometers are commercially available. By true we mean an accelerometer which would pick up the three components of point-accelerations using one single proof-mass. What we propose is novel architecture classes of parallel-kinematics-machine for multi-axial accelerometers, that is, accelerometers that can measure n components of point-accelerations, where n = 1, 2, 3. We call these architectures simplectic, as they use n + 1 legs oriented normally to the n + 1 faces of the regular simplex associated with the n-dimensional subspace of measured acceleration components. We show that the simplectic biaxial accelerometer can be fabricated using micromachining MEMS techniques, while the simplectic triaxial accelerometer lends itself to compliant-mechanism fabrication techniques. CAD models of the prototypes proposed are provided for all of the three novel mechanical architectures proposed. Finally, the direct kinematics problems associated with the simplectic biaxial and triaxial accelerometers are shown to be linear in both cases. This feature simplifies the estimation of the proof-mass displacement from piezoresistive or piezoelectric measurements taken at the flexible joints connecting the legs of the mechanism to the rigid body whose acceleration is under estimation.