
fidelity digital twin and a deep learning model to
diagnose actuator-level faults in a 6-DOF industrial
robot (St
¨
aubli TX60). While several works have ex-
plored the use of recurrent neural networks (RNNs)
for time-series classification, we focus here on Gated
Recurrent Units (GRU), a variant of RNNs known
for its computational efficiency and ability to capture
long-term dependencies in sequential data (Cho et al.,
2014). GRU are particularly suitable for robotic fault
diagnosis, where the temporal evolution of joint tra-
jectories provides essential clues for identifying fail-
ure types and their onset times. The proposed contri-
bution consists in (i) developing a comprehensive dig-
ital twin in MATLAB Simulink and Simscape Multi-
body, capable of replicating both nominal and faulty
dynamics of the TX60 robot; (ii) implementing a
structured fault injection module that introduces ran-
dom motor blockages at selected instants (e.g., 0.1
s, 0.4 s, 0.5 s); (iii) generating a labeled dataset of
time-series responses; and (iv) training a GRU-based
neural network classifier in Python to distinguish be-
tween 49 different scenarios (48 faults + 1 normal
state). Our methodology is illustrated in Figure 1,
which summarizes the full pipeline—from fault sim-
ulation to neural classification. The real robot serves
as a validation reference, while the digital twin pro-
duces repeatable scenarios for training and evalua-
tion. Fault signatures extracted from joint trajecto-
ries are used to teach the model how to recognize dis-
tinct fault types and their corresponding time profiles.
The remainder of this paper is structured as follows.
Section 2 details the proposed methodology, includ-
ing the digital twin setup, data generation strategy,
and GRU-based classification approach. Section 3
presents the digital twin architecture and fault simu-
lation procedures. Section 4 describes the data prepa-
ration pipeline and neural network training. Section 5
discusses the model’s performance through accuracy
plots, confusion matrix, and detailed classification
metrics. Finally, conclusions and future directions are
outlined in Section 6.
2 METHODOLOGY
The proposed methodology, illustrated in Figure 1,
combines a physics-based digital twin with a data-
driven deep learning classifier to enable accurate fault
diagnosis on the St
¨
aubli TX60 robotic arm. The real
system serves as a reference for validating the be-
havior of a high-fidelity virtual replica developed in
MATLAB Simulink and Simscape Multibody.
This digital twin replicates both nominal and
faulty conditions and includes a fault injection mod-
ule that simulates motor blockage at predefined in-
stants (e.g., 0.1 s, 0.4 s, 0.5 s) to generate diverse
and controlled fault scenarios. These simulations pro-
duce time series representing joint angles and end-
effector positions, which are then collected and seg-
mented into sequences of 10 time steps. The result-
ing labeled dataset, composed of 49 distinct classes
(48 fault scenarios and one nominal state), is used
to train a Gated Recurrent Unit (GRU) neural net-
work. GRU is a variant of recurrent neural networks
optimized for temporal pattern recognition, offering
a simplified architecture compared to LSTMs while
maintaining performance in sequence modeling (Cho
et al., 2014). The model is trained in Python over
100 epochs using the Adam optimizer and categor-
ical cross-entropy loss. Stratified splitting ensures
class balance across training and test sets. This inte-
grated simulation-learning framework provides a re-
producible and non-destructive approach for diagnos-
ing robotic joint faults under dynamic conditions.
3 DIGITAL TWIN AND FAULT
SIMULATION
The concept of the digital twin plays a central role
in modern fault detection strategies. It enables real-
time simulation, fault injection, and behavioral anal-
ysis without relying on physical hardware. In this
work, a digital twin of the St
¨
aubli TX60 industrial
robot was developed to replicate both its nominal and
faulty operations. This twin was used to generate rep-
resentative data under different scenarios for training
and evaluating a neural network-based diagnoser.
3.1 Digital Model of the Robotic System
To accurately represent the behavior of the St
¨
aubli
TX60 robot, a high-fidelity digital twin was devel-
oped using MATLAB Simulink and Simscape Multi-
body (Boschetti and Sinico, 2024). This digital model
reproduces the kinematic and dynamic characteristics
of the robot under nominal conditions and serves as
a reference for fault diagnosis. The CAD structure of
the robot was imported in STEP format and integrated
into the Simscape environment via the Simulink in-
terface. The kinematic chain was reconstructed, and a
dynamic model was built using polynomial trajectory
generation, inverse and forward kinematics, and joint
actuation. Each joint is actuated by a dedicated motor,
and the control architecture relies on feedback loops
to track desired trajectories. The model simulates the
3D motion of the end-effector as it follows prede-
fined paths, such as square trajectories in Cartesian
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