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First set of proposed msgs for setting up Cartesian Impedance parameters #1

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First set of proposed msgs for setting up Cartesian Impedance parameters #1

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35752d3
Setting up initial project for CartesianImpedance.
rkojcev May 28, 2016
cca87a3
update README
rkojcev May 28, 2016
cc0e82b
update readme.
rkojcev May 28, 2016
1496a01
Initial message construction. For now only stifness and damping are b…
rkojcev Jun 5, 2016
0dacffc
Remove unused msgs
rkojcev Jun 5, 2016
8a97db5
Added all msgs for setting Cartesian Impedance parameters.
rkojcev Jun 9, 2016
217c48a
SetCartesianImpedance.msg expanded with all params
rkojcev Jun 9, 2016
e718728
small readme updates
rkojcev Jun 9, 2016
de428b4
Expanding messages. Adding error description
rkojcev Jun 10, 2016
3190ca8
Improving documentation
rkojcev Jun 10, 2016
7a7691f
Removing links from msg description.
rkojcev Jun 16, 2016
c807454
Adding tool field name, for now is defined as string. Adding addition…
rkojcev Jun 17, 2016
52dcb39
Adding CartesianDampingRatio msgs, for robots that use ratios for set…
rkojcev Jun 20, 2016
dd04da2
only one damping msg now using ratio's.
rkojcev Jun 20, 2016
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1 change: 1 addition & 0 deletions cartesian_impedance_msgs/CMakeLists.txt
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Expand Up @@ -15,6 +15,7 @@ add_message_files(DIRECTORY msg
FILES
CartesianStiffness.msg
CartesianDamping.msg
CartesianDampingRatio.msg
MaxCartesianVelocity.msg
MaxControlForce.msg
MaxPathDeviation.msg
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4 changes: 2 additions & 2 deletions cartesian_impedance_msgs/msg/CartesianDamping.msg
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Expand Up @@ -7,7 +7,7 @@
# oscillate after deflection.
# For all degrees of freedom (without unit: Lehr’s damping ratio)

# [ratio:0.1-1.0]
# [Ns/m]
geometry_msgs/Vector3 translational
# [ratio:0.1-1.0]
# [Ns/rad]
geometry_msgs/Vector3 rotational
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@shaun-edwards shaun-edwards Jun 9, 2016

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In this context, what does rotational damping mean? I assume it's dampening about the fixed frame axes? Is there any confusion/issues like those associated with euler angles (i.e. order of application)?

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@rkojcev rkojcev Jun 9, 2016

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Yes you are right Shaun. Is dampening about the fixed frame axes. These values are usually consistent and each value during the motion is constant, so there are no singularities that come with Euler angles actually these are just constants which are used to define the properties of the Spring when the robot is in Cartesian Impedance Mode.

13 changes: 13 additions & 0 deletions cartesian_impedance_msgs/msg/CartesianDampingRatio.msg
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# Damping parameters for the Cartesian Impedance
# the values are divided into translational and rotational
# each of the translational and rotational components is defined as Vector3

# Spring damping (type: double)
# The spring damping determines the extent to which the virtual springs
# oscillate after deflection.
# For all degrees of freedom (without unit: Lehr’s damping ratio)

# [ratio:0.1-1.0]
geometry_msgs/Vector3 translational
# [ratio:0.1-1.0]
geometry_msgs/Vector3 rotational
4 changes: 2 additions & 2 deletions cartesian_impedance_msgs/msg/NullSpace.msg
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Expand Up @@ -11,8 +11,8 @@
string[] link_names

# [Nm/rad] must be => 0.0
std_msgs/Float64[] stiffness
float64[] stiffness

# without unit: Lehr’s damping ratio
# must be between 0.3-1.0 suggested is 0.7
std_msgs/Float64[] damping
float64[] damping
17 changes: 10 additions & 7 deletions cartesian_impedance_msgs/msg/SetCartesianImpedance.msg
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# Here we combine all the parameters message definitions into a single message
# that needs to be send to the controller in order to adjust the Cartesian Impedance Parameters

string tool
CartesianStiffness stiffness
CartesianDamping damping
MaxCartesianVelocity max_cart_vel
MaxControlForce max_ctrl_force
MaxPathDeviation max_path_deviation
NullSpace null_space_params
string tool
CartesianStiffness stiffness
#use this if the damping is in Ns/m, Ns/rad
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@shaun-edwards shaun-edwards Jun 20, 2016

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How does the receiving node know which type of Cartesian stiffness is used?

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@rkojcev rkojcev Jun 20, 2016

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Do you mean Cartesian Damping type?

For now the only difference is in the naming, and is up to the user to decide which one to choose. In fact there is not even difference of the variable definition.

Do you have any suggestions how we can differentiate this better, or we could just leave one msg type called damping and let the user either input ratio or Ns/m for the damping parameters. Having two types of damping msgs can be confusing and prone to errors

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@shaun-edwards shaun-edwards Jun 20, 2016

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Yes, I meant dampening.

From a usability perspective, any publisher and any subscriber should be able to talk and the semantic intent of the message should be clear. In other words, the messages sent should always mean the same thing regardless of who is producing/consuming it.

I think you should pick convention and then make sure subscribers can translate that convention into whatever is expected by the controller. For example, if you pick Ns/m, then the drive node for the iiwa will require a critical dampening parameter(s) in order to translate into a unit-less dampening. While this may seem like it makes the driver more complex, it does so for the sake of usability and consistent semantics.

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@gavanderhoorn gavanderhoorn Jun 20, 2016 •
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If I may make a suggestion, I think the choice for either ratio or Ns/m is something we should get as much input on as possible.

I've talked to multiple people internally (control engineers, mechanical engineers, ..) and have heard passionate arguments for and against both options. Some find ratios much more intuitive, others dislike the relativeness of them. Ns/m is regarded as difficult, and not as 'platform independent' (ie: 0.5 is always 0.5, but the effect of 1.0 Ns/m isn't immediately clear), even though it is something that actually has a unit (and is not a dimensionless nr, so is less ambiguous / depending on context).

Personally I agree with @shaun-edwards (and I think I've said it before), in that any message should be unambiguously interpretable. Making the semantics of fields dependent on implicit or invisible assumptions / knowledge seems like a bad idea.

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@rkojcev rkojcev Jun 20, 2016

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I also agree with @gavanderhoorn that we should definitely find consensus whether we should use ratio's or Ns/m, I think that this should highly depend on the units majority of the robots use as well. I am also looking at how to convert from Ns/m to ratios for example and it seems it is not very straight forward thing to do...

Maybe if we can get input from others who have robots who use Cartesian Impedance and the units they use would be great.

CartesianDamping damping
#use this if the damping parameters are defined as ratios (Lehr's damping ratio)
CartesianDampingRatio damping_ratio
MaxCartesianVelocity max_cart_vel
MaxControlForce max_ctrl_force
MaxPathDeviation max_path_deviation
NullSpace null_space_params