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A compact pen-type force sensor is developed to study the feasibility of force-based signature verification. A force-sensing method based on leverage effect is proposed to detect 3-D forces between the pen's tip and the paper. A compact and low-cost force-sensing assembly is designed, which is integrated by five off-the-shelf 1-D force sensors. A matrix-based measurement model is established to compute the force signal in the task coordinate system (CS), which is transformed from the force signal in the sensor CS and the angle signal from a 2-D angle sensor. The structural parameters of the force sensor are determined both to achieve the required force accuracy and to meet the constraints of pen size for comfortable grasping. System performance experiments are carried out to measure the absolute and repetitive accuracy of the pen. The results show that the pen is capable for detection of 3-D force signals during real-time handwriting. Repetitive accuracy is measured to be about 0.05 N. Finally, a small-scale signature verification experiment is carried out. The verification results based on the dynamic time warping (DTW) method show that the equal error rate (EER) is about 6.3%, which illustrates the potential of the pen for force-based signature verification.