Robot gripper cannot grasp cloth (slipping problem)

[vrg15101]

slipping.webm I tried to reduce the substeps and tried doing both force and position control for the end effector and it does not seem to help. The gripper is not able to pick up the cloth and maintain constant contact.

[zswang666]

Looks like there is coupling force between the gripper and the cloth as there is one particle moves seemingly due to the gripper. Could you provide the script you are running?

[vrg15101]

Thank you for your response, here is the code,

import genesis as gs
import numpy as np
import IPython

########################## init ##########################
gs.init()

########################## create a scene ##########################

scene = gs.Scene(
sim_options=gs.options.SimOptions(
dt=0.01,
substeps=5,
),
coupler_options = gs.options.CouplerOptions(rigid_pbd = True,),
rigid_options=gs.options.RigidOptions(enable_collision=True,),
pbd_options=gs.options.PBDOptions(
particle_size = 0.01,
gravity = (0,0,-9.8),
),
viewer_options=gs.options.ViewerOptions(
camera_fov=30,
res=(1280, 720),
max_FPS=60,
),
show_viewer=True,
)

########################## entities ##########################
plane = scene.add_entity(
morph=gs.morphs.Plane(),
)

cloth_1 = scene.add_entity(
material=gs.materials.PBD.Cloth(),
morph=gs.morphs.Mesh(
file="meshes/cloth.obj",
scale=2.0,
pos=(0, 0, 0.01),
euler=(0.0, 0, 0.0),
collision = True,
),
surface=gs.surfaces.Default(
color=(0.2, 0.4, 0.8, 1.0),
vis_mode="particle",
),
)
franka = scene.add_entity(
gs.morphs.MJCF(
file="xml/franka_emika_panda/panda.xml",
pos = (-0.5,0.0,0.0),
),
material=gs.materials.Rigid(coup_friction=4.0),
)

########################## build ##########################
scene.build()

cloth_1.set_particle_position(0,np.array([0.0,0.0,0.25], dtype=np.float32))
scene.step()
#cloth_1.fix_particle(0)
cloth_1.fix_particle(cloth_1.find_closest_particle((1, 1, 0.0)))
velocity = np.array([0.10, 0.10, 0.10], dtype=np.float32)
scene.step()
fixed_point_pos = cloth_1.get_particles()[0]
fixed_point_pos[2] =fixed_point_pos[2] +0.2
####IPython.embed()

motors_dof = np.arange(7)
fingers_dof = np.arange(7, 9)

franka.set_dofs_kp(
np.array([4500, 4500, 3500, 3500, 2000, 2000, 2000, 100, 100]),
)
franka.set_dofs_kv(
np.array([450, 450, 350, 350, 200, 200, 200, 10, 10]),
)
franka.set_dofs_force_range(
np.array([-87, -87, -87, -87, -12, -12, -12, -100, -100]),
np.array([ 87, 87, 87, 87, 12, 12, 12, 100, 100]),
)

end_effector = franka.get_link('hand')

qpos = franka.inverse_kinematics(
link = end_effector,
pos = fixed_point_pos,#np.array([-0.75, 0.0, 0.5]),
quat = np.array([0, 1, 0, 0]),
)
qpos[-2:] = 0.04
path = franka.plan_path(
qpos_goal = qpos,
num_waypoints = 200, # 2s duration
)

for waypoint in path:
franka.control_dofs_position(waypoint)
scene.step()

for i in range(100):
scene.step()

reach_pos = cloth_1.get_particles()[0]
reach_pos[2] = reach_pos[2]+0.085
qpos = franka.inverse_kinematics(
link = end_effector,
pos = reach_pos,
quat = np.array([0, 1, 0, 0]),
)

franka.control_dofs_position(qpos[:-2], motors_dof)
for i in range(100):
scene.step()

franka.control_dofs_position(qpos[:-2], motors_dof)
franka.control_dofs_position(np.array([0.001, 0.001]), fingers_dof) # you can use position control
#franka.control_dofs_force(np.array([-0.5, -0.5]), fingers_dof)

for i in range(200):
scene.step()

for i in range(300):
qpos = franka.inverse_kinematics(
link=end_effector,
pos=np.array([0.0, 0.0, reach_pos[2] + 0.0005 * i]),
quat=np.array([0, 1, 0, 0]),
)
franka.control_dofs_position(qpos[:-2], motors_dof)
scene.step()
for i in range(200):
scene.step()
for i in range(1000):
scene.step()