Spatial force measurement using a rigid hexapod-based end-effector with structure-integrated force sensors in a hexapod machine tool

Model Calibration for a Rigid Hexapod-Based End-Effector with Integrated Force Sensors

“…In production, many manufacturing applications, such as process diagnosis and quality assurance, or adaptive process control for milling, grinding or thermo-smoothing, require in-process force measurement, where, in particular, the measurement of spatial forces and moments in 6 degrees of freedom (DoF) is requested [1]. As one approach, Refs.…”

“…As one approach, Refs. [1][2][3] present a new measuring system using a hexapod-based end-effector with structure-integrated sensors. Six 1 DoF force sensors are integrated into a rigid bar framework and the measured forces are transformed to Cartesian forces and moments at the tool centre point (TCP) by a control-integrated model.…”

“…Compared to a drive current based force measurement in spindle drives, it is far more accurate (factor 100 smaller uncertainty [2]) and requires less modelling effort, since no non-linear and stochastic mechanical influences of drive components interfere such as friction, stick-slip effects or elastic deformation. Altogether, structure-integrated force measurement has many benefits and can complement or replace the measurement by the use of conventional FT sensors as long as it provides a 6 DoF measurement, fulfils accuracy and stiffness requirements, and is simple to parametrise [1]. In addition, integrated sensors can be supplied by the machine manufacturer and make force measurement and control an easyto-use machine-integrated feature in the future.…”

“…Machine-integrated force measurement solutions have been studied since the beginning of force measurement and are outlined in a detailed state-of-the-art overview in [1]. In short, individual strain-gauge based solutions with a specific design, such as spindles [4], end-effectors [5], or even the workpiece [6], are cost-intensive and do not, thus far, provide a spatial measurement in 6 DoF.…”

“…Instead, for the presented moving sensor system that is the end-effector of a parallel kinematic machine tool, a real-time capable measurement model, which runs within the numeric control system, is essential. As shown in [1,2], an accurate and precise spatial force measurement and competitive characteristics (resolution, range, overload), when compared to a commercial FT sensor, can be realised in the entire workspace by the use of a rigid body dynamic, a sensor and an error compensation model. The stiffness loss at the TCP by sensor integration is comparable to a commercial FT sensor, as presented in [3].…”