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Press Force

The force stage trims the raw press signals (force/data) to the forming window and removes the load-cell rest offset, producing a fixed 600-row table. It runs as part of rddac preprocess; parameters can be overridden via --config.

Property Raw Processed
Shape variable, ~(1140, 8) or ~(720, 8) depending on press speed fixed (600, 8) float32
Columns time, load_cell_1..4, punch_temp, punch_pos, total_force unchanged, all 8 kept
Time range 0 to ~3.8 s 0 to 2 s (re-zeroed)
Sampling rate 300 Hz unchanged

Why this stage exists

The raw recording spans the complete machine cycle (startup, forming, retraction), but only the forming phase carries process information, and its position inside the recording varies with the blankholder force (lower force → slower cycle). The load cells also rest at the blankholder preload rather than zero, so absolute values are not comparable across experiments until the baseline is removed.

All eight columns are kept. punch_pos is the punch trajectory, the natural kinematic axis for force-vs-position views. punch_temp is near-constant over one stroke (its mean is already a root attribute), but keeping it costs nothing and preserves the published force-curve field mapping unchanged.

Processing steps

  1. Window trimming: samples outside \((0.25\ \text{s},\ 2.25\ \text{s}]\) are startup/shutdown noise and are dropped; at 300 Hz the window yields exactly 600 rows. Time is re-zeroed to the window start.
  2. Rest-offset removal: each load cell (and the total force) has its in-window minimum subtracted, so every curve starts from zero.
  3. Quantization: time to 4 decimals (s), forces to 0.01 kN, temperature to 0.1 °C, punch position to the 0.5 mm encoder resolution.

Raw force curves with the forming-window boundaries (left) and the processed, offset-free curves on the re-zeroed time axis (right).

Parameters

TOML key ([force]) Default Meaning
time_window_start 0.25 window start in s (exclusive)
time_window_end 2.25 window end in s (inclusive)
position_precision_mm 0.5 punch-position quantization step

Row counts and the parameter values used are stamped into the force group attributes.

Further reading