---
license: apache-2.0
library_name: robomimic
pipeline_tag: robotics
tags:
- robotics
- diffusion-policy
- imitation-learning
- lerobot
- variable-admittance
- force-control
- doosan
datasets:
- aleleanza/vac-fridge-single-cam
---

# Diffusion Policy — VAC Fridge (input/output ablation)

Eight **robomimic Diffusion Policy** checkpoints for the **variable-impedance pick**
("fridge") task on a Doosan M0609 + Inspire RH56 hand under a **Variable Admittance
Controller (VAC)**. Trained on
[`aleleanza/vac-fridge-single-cam`](https://huggingface.co/datasets/aleleanza/vac-fridge-single-cam)
(200 episodes, 54,833 frames @ 20 Hz, single RGB camera).

This is the fridge-task counterpart of
[`aleleanza/diffusion-policy-vac-pipe`](https://huggingface.co/aleleanza/diffusion-policy-vac-pipe):
an ablation over two *output* representations (relative to the admittance filter) ×
input modality, plus a larger-UNet variant per side.

## Variants (subfolders)

| Subfolder | Output (action) | Inputs (obs) | Action dim | Best val loss | @epoch |
|---|---|---|---:|---:|---:|
| `vac_preimg` | **pre**: `user_cmd[6]` + `K` + `ζ` + `hand_binary` | vision | 9 | 0.11807 | 240 |
| `vac_preimg_state` | pre | vision + state | 9 | 0.09940 | 240 |
| `vac_preimg_state_wrench` | pre | vision + state + wrench | 9 | 0.10013 | 597 |
| `vac_preimg_state_wrench_big` | pre (larger UNet) | vision + state + wrench | 9 | 0.10529 | 275 |
| `vac_postimg` | **post**: `vel_cmd[6]` + `hand_binary` | vision | 7 | 0.10254 | 240 |
| `vac_postimg_state` | post | vision + state | 7 | 0.09851 | 193 |
| `vac_postimg_state_wrench` | post | vision + state + wrench | 7 | **0.09467** | 193 |
| `vac_postimg_state_wrench_big` | post (larger UNet) | vision + state + wrench | 7 | 0.10136 | 263 |

- **pre** = predict the operator command *before* admittance, including the compliance
  command itself (`stiffness_cmd` K + damping ζ) → the policy *learns to set compliance*.
- **post** = predict the Cartesian velocity executed *after* admittance → bypasses the
  admittance filter and drives velocity directly.

Each subfolder contains: `best.pth`, `last.pth`, `config.json`, `action_stats.json`
(action min-max normalization + components + hand binarization), `dataset_summary.json`
(train/valid split).

## Architecture & training

- **Algorithm:** robomimic Diffusion Policy (DDPM noise-prediction loss).
- **Backbone:** conditional UNet `[128, 256, 512]`; the `_big` variants use
  `[256, 512, 1024]` (~91.8M params vs ~89.4M).
- **Horizons:** observation 2, action 4, prediction 8 (frame stack 2, seq length 8).
- **Image:** single camera → `front_rgb`, **84×84**.
- **Diffusion:** DDPM 50 train/infer steps (DDIM 10-step configurable for faster inference).
- **Schedule:** up to 600 epochs, batch 16, lr 1e-4.
- **`state`** is built at runtime from current TCP + Inspire hand joints; **`wrench`** from
  `/bota_ft_sensor/wrench`. Hand head is **binarized** (`hand_open_binary`).

### Reading the results

Validation losses are tightly clustered (~0.095–0.118). Adding **state** helps both pre
and post; the best overall is **`vac_postimg_state_wrench`** (0.0947). The larger-UNet
(`_big`) variants did **not** improve validation at this dataset size. Post (vel_cmd)
targets are marginally easier than pre (user_cmd + K + ζ), consistent with the pipe
ablation though the gap here is much smaller.

## Inference (ROS 2)

Run with the project's `robot_learning` real-time inference nodes (Doosan M0609 + Inspire
hand). The action contract determines the runner:

- **`pre*` variants (9D)** → `diffusion_policy_vac_preimg_runner`: publishes
  `action[:6]→/delta_pose_cmd`, `[6]→/predicted_K`, `[7]→/predicted_zeta`,
  `[8]→/inspire_hand/left/cmd`; consumed by `variable_admittance_node` (`variable_K:=true`).
- **`post*` variants (7D)** → `diffusion_policy_fixed_k_runner` in `vel_cmd` mode: streams
  velocity directly via the DSR `speedl` interface (no admittance node).

Pre-wired launchers exist under `robot_learning/scripts/` (e.g.
`launch_vac_inference.sh preimg_state_wrench`); `*_wrench*` variants additionally need the
Bota driver. `action_stats.json` provides the exact normalization to undo at inference.

## Intended use & limitations

- **Use:** research on force-aware / compliance-predicting imitation learning; VAC baselines.
- **Limitations:** single task, single embodiment (M0609 + RH56), single 84×84 camera,
  binary hand. Validation differences between variants are small. Not validated for
  safety-critical or autonomous deployment.

## Related

- **Dataset:** [`aleleanza/vac-fridge-single-cam`](https://huggingface.co/datasets/aleleanza/vac-fridge-single-cam)
- **Pipe counterpart:** [`aleleanza/diffusion-policy-vac-pipe`](https://huggingface.co/aleleanza/diffusion-policy-vac-pipe)
- **Collection:** *VAC — Fridge*