LoadCarrierDB

Introduction

The LoadCarrierDB module (Load carrier database module) allows the global definition of load carriers, which can then be used in many detection modules. The specified load carriers are available for all modules supporting load carriers on the rc_visard.

The LoadCarrierDB module is a base module which is available on every rc_visard.

Table 53 Specifications of the LoadCarrierDB module

Supported load carrier types	4-sided or 3-sided
Supported rim types	solid rim, stepped rim or ledged rim
Min. load carrier dimensions	0.1 m x 0.1 m x 0.05 m
Max. load carrier dimensions	2 m x 2 m x 2 m
Max. number of load carriers	50
Load carriers available in	ItemPick and BoxPick and SilhouetteMatch
Supported pose types	no pose, orientation prior, exact pose
Supported reference frames	camera, external

Load carrier definition

A load carrier (bin) is a container with four walls, a floor and a rectangular rim, which can contain objects. It can be used to limit the volume in which to search for objects or grasp points.

A load carrier is defined by its outer_dimensions and inner_dimensions. The maximum outer_dimensions are 2.0 meters in every dimension.

The origin of the load carrier reference frame is in the center of the load carrier’s outer box and its z axis is perpendicular to the load carrier’s floor pointing outwards (see Fig. 57).

Fig. 57 Load carrier with reference frame and inner and outer dimensions

Note

Typically, outer and inner dimensions of a load carrier are available in the specifications of the load carrier manufacturer.

The inner volume of the load carrier is defined by its inner dimensions, but includes a region of 10 cm height above the load carrier, so that also items protruding from the load carrier are considered for detection or grasp computation. Furthermore, an additional crop_distance is subtracted from the inner volume in every dimension, which acts as a safety margin and can be configured as run-time parameter in the LoadCarrier module (see Parameters). Fig. 58 visualizes the inner volume of a load carrier. Only points which are inside this volume are considered for detections.

Fig. 58 Visualization of the inner volume of a load carrier. Only points which are inside this volume are considered for detections.

Since the load carrier detection is based on the detection of the load carrier’s rim, the rim geometry must be specified if it cannot be determined from the difference between outer and inner dimensions. A load carrier with a stepped rim can be defined by setting a rim_thickness. The rim thickness gives the thickness of the outer part of the rim in the x and y direction. When a rim thickness is given, an optional rim_step_height can also be specified, which gives the height of the step between the outer and the inner part of the rim. When the step height is given, it will also be considered during collision checking (see CollisionCheck). Examples of load carriers with stepped rims are shown in Fig. 59 A, B. In addition to the rim_thickness and rim_step_height the rim_ledge can be specified for defining load carriers whose inner rim protrudes into the interior of the load carrier, such as pallet cages. The rim_ledge gives the thickness of the inner part of the rim in the x and y direction. An example of a load carrier with a ledged rim is shown in Fig. 59 C.

Fig. 59 Examples of load carriers with stepped rim (A, B) or ledged rim (C)

The different rim types are applicable to both, standard 4-sided and 3-sided load carriers. For a 3-sided load carrier, the type must be THREE_SIDED. If the type is set to STANDARD or left empty, a 4-sided load carrier is specified. A 3-sided load carrier has one side that is lower than the other three sides. This height_open_side is measured from the outer bottom of the load carrier. The open side is at the negative y-axis of the load carrier’s coordinate system. Examples of the two load carrier types are given in Fig. 60. The height of the lower side is only considered during collision checking and not required for the detection of the load carrier.

Fig. 60 Examples of a standard 4-sided load carrier (A) and a 3-sided load carrier (B)

A load carrier can be specified with a full 3D pose consisting of a position and an orientation quaternion, given in a pose_frame. Based on the given pose_type this pose is either used as an orientation prior (pose_type is ORIENTATION_PRIOR or empty), or as the exact pose of the load carrier (pose_type is EXACT_POSE).

In case the pose serves as orientation prior, the detected load carrier pose is guaranteed to have the minimum rotation with respect to the load carrier’s prior pose. This pose type is useful for detecting tilted load carriers and for resolving the orientation ambiguity in the x and y direction caused by the symmetry of the load carrier model.

In case the pose type is set to EXACT_POSE, no load carrier detection will be performed on the scene data, but the given pose will be used in exactly the same way as if the load carrier is detected at that pose. This pose type is especially useful in cases where load carriers do not change their positions and/or are hard to detect (e.g. because their rim is too thin or the material is too shiny).

The rc_visard can persistently store up to 50 different load carrier models, each one identified by a different id. The configuration of a load carrier model is normally performed offline, during the set up the desired application. This can be done via the REST-API interface or in the rc_visard Web GUI.

Note

The configured load carrier models are persistent even over firmware updates and rollbacks.

Load carrier compartments

Some detection modules can make use of a load_carrier_compartment to further limit the volume for the detection, for example ItemPick’s compute_grasps service. A load carrier compartment is a box whose pose is defined as the transformation from the load carrier reference frame to the compartment reference frame, which is located in the center of the compartment box (see Fig. 61). The load carrier compartment is defined for each detection call separately and is not part of the load carrier definition in the LoadCarrierDB module.

Fig. 61 Sample compartment inside a load carrier. The coordinate frame shown in the image is the reference frame of the compartment.

The compartment volume is intersected with the load carrier inner volume to compute the volume for the detection. If this intersection should also contain the 10 cm region above the load carrier, the height of the compartment box must be increased accordingly.

Interaction with other modules

Internally, the LoadCarrierDB module depends on, and interacts with other on-board modules as listed below.

Hand-eye calibration

In case the camera has been calibrated to a robot, the load carrier’s exact pose or orientation prior can be provided in the robot coordinate frame by setting the corresponding pose_frame argument to external.

Two different pose_frame values can be chosen:

1. Camera frame (camera). The load carrier pose or orientation prior is provided in the camera frame, and no prior knowledge about the pose of the camera in the environment is required. This means that the configured load carriers move with the camera. It is the user’s responsibility to update the configured poses if the camera frame moves (e.g. with a robot-mounted camera).
2. External frame (external). The load carrier pose or orientation prior is provided in the external frame, configured by the user during the hand-eye calibration process. The module relies on the on-board Hand-eye calibration module to retrieve the sensor mounting (static or robot mounted) and the hand-eye transformation.

Note

If no hand-eye calibration is available, all pose_frame values should be set to camera.

All pose_frame values that are not camera or external are rejected.

Services

The LoadCarrierDB module is called rc_load_carrier_db in the REST-API and is represented in the Web GUI under Database ‣ Load Carriers. The user can explore and call the LoadCarrierDB module’s services, e.g. for development and testing, using the REST-API interface or the Web GUI.

The LoadCarrierDB module offers the following services.

set_load_carrier

Persistently stores a load carrier on the rc_visard. All configured load carriers are persistent over firmware updates and rollbacks.

Details

This service can be called as follows.

PUT http://<host>/api/v2/nodes/rc_load_carrier_db/services/set_load_carrier

Request

Response

Details for the definition of the load_carrier type are given in Load carrier definition.

The field type is optional and accepts STANDARD and THREE_SIDED.

The field pose_type is optional and accepts NO_POSE, EXACT_POSE and ORIENTATION_PRIOR.

The definition for the request arguments with corresponding datatypes is:

{
  "args": {
    "load_carrier": {
      "height_open_side": "float64",
      "id": "string",
      "inner_dimensions": {
        "x": "float64",
        "y": "float64",
        "z": "float64"
      },
      "outer_dimensions": {
        "x": "float64",
        "y": "float64",
        "z": "float64"
      },
      "pose": {
        "orientation": {
          "w": "float64",
          "x": "float64",
          "y": "float64",
          "z": "float64"
        },
        "position": {
          "x": "float64",
          "y": "float64",
          "z": "float64"
        }
      },
      "pose_frame": "string",
      "pose_type": "string",
      "rim_ledge": {
        "x": "float64",
        "y": "float64"
      },
      "rim_step_height": "float64",
      "rim_thickness": {
        "x": "float64",
        "y": "float64"
      },
      "type": "string"
    }
  }
}

The definition for the response with corresponding datatypes is:

{
  "name": "set_load_carrier",
  "response": {
    "return_code": {
      "message": "string",
      "value": "int16"
    }
  }
}

get_load_carriers

Returns the configured load carriers with the requested load_carrier_ids. If no load_carrier_ids are provided, all configured load carriers are returned.

Details

This service can be called as follows.

PUT http://<host>/api/v2/nodes/rc_load_carrier_db/services/get_load_carriers

Request

Response

The definition for the request arguments with corresponding datatypes is:

{
  "args": {
    "load_carrier_ids": [
      "string"
    ]
  }
}

The definition for the response with corresponding datatypes is:

{
  "name": "get_load_carriers",
  "response": {
    "load_carriers": [
      {
        "height_open_side": "float64",
        "id": "string",
        "inner_dimensions": {
          "x": "float64",
          "y": "float64",
          "z": "float64"
        },
        "outer_dimensions": {
          "x": "float64",
          "y": "float64",
          "z": "float64"
        },
        "pose": {
          "orientation": {
            "w": "float64",
            "x": "float64",
            "y": "float64",
            "z": "float64"
          },
          "position": {
            "x": "float64",
            "y": "float64",
            "z": "float64"
          }
        },
        "pose_frame": "string",
        "pose_type": "string",
        "rim_ledge": {
          "x": "float64",
          "y": "float64"
        },
        "rim_step_height": "float64",
        "rim_thickness": {
          "x": "float64",
          "y": "float64"
        },
        "type": "string"
      }
    ],
    "return_code": {
      "message": "string",
      "value": "int16"
    }
  }
}

delete_load_carriers

Deletes the configured load carriers with the requested load_carrier_ids. All load carriers to be deleted must be explicitly stated in load_carrier_ids.

Details

This service can be called as follows.

PUT http://<host>/api/v2/nodes/rc_load_carrier_db/services/delete_load_carriers

Request

Response

The definition for the request arguments with corresponding datatypes is:

{
  "args": {
    "load_carrier_ids": [
      "string"
    ]
  }
}

The definition for the response with corresponding datatypes is:

{
  "name": "delete_load_carriers",
  "response": {
    "return_code": {
      "message": "string",
      "value": "int16"
    }
  }
}

Return codes

Each service response contains a return_code, which consists of a value plus an optional message. A successful service returns with a return_code value of 0. Negative return_code values indicate that the service failed. Positive return_code values indicate that the service succeeded with additional information. The smaller value is selected in case a service has multiple return_code values, but all messages are appended in the return_code message.

The following table contains a list of common codes:

Table 54 Return codes of the LoadCarrierDB module’s services

Code	Description
0	Success
-1	An invalid argument was provided
-10	New element could not be added as the maximum storage capacity of load carriers has been exceeded
10	The maximum storage capacity of load carriers has been reached
11	An existent persistent model was overwritten by the call to set_load_carrier