Today's highly sophisticated manufacturing and assembly applications
require precise part fitting, flawless assembly, and efficient material removal
techniques. This is especially true in industries where gear matching, machine
tooling, and automotive or construction equipment manufacturing is performed.
Manufacturers strive to improve these processes, increase production quality,
all while achieving lower costs. Force sensing and robotic vision techniques
have been introduced into industry as an added enhancement to the proven effectiveness
of robots in manufacturing.
Force sensors can be applied in
the robotic system to control velocity and force when objects are fit, aligned,
buffed, trimmed, or assembled thereby improving product quality and process
integrity. Force sensors are integrated to provide intelligent robots that
can feel enabling the most demanding mechanical
assembly and material removal operations. Force sensors can detect the force
and moment (x, y, z, yaw, pitch, and roll) applied to it from external sources.
In addition, tolerances can be defined, measured and tested for a consistent
and repeatable environment since precision assembly can be performed to within
an accuracy of 2%.
Force control enables the robot to perform the following operations:
Precise fitting of machine parts
Gear teeth engagement
Push under constant force and product life cycle tests (automotive
door operation, switching operations, applications requiring constant force)
Alignment of flat surface of one workpiece with a flat surface
of another workpiece
Grinding a workpiece with a grinder or sander
At FANUC America, the force sensor consists of a sensor head, sensor
adapter, and sensor cable. Two kinds of force sensors exist:
Remote or Fixture-Mounted where the force sensor is mounted
on a fixture or in a location remotely from the robot. The robot
holds the part and presents it to the Force Sensor.
Faceplate-Mounted where the force sensor is mounted to the
robot faceplate. The robot holds the force sensor and presents it to the part.
Force data charting on the iPendant user interface device
allows continuous display of actual force variations during the force control
Several algorithms are used to enhance force sensing:
Constant Push / Face Match
Constant Push allows for a soft push of a workpiece at a single point,
such as for the arrangement of components along a guide.
Face Match allows for matching the face of the workpiece held in the
robot hand with the face of the object, such as when a workpiece is inserted
into the chuck of a machine tool.
Shaft Insert / Bearing Insert / Groove Insert / Square Insert/Clutch
Insertion of varying shapes such as cylindrical, half-moon shape workpiece
such as engine main bearings, a workpiece into a groove, or a quadrangular
prism (square) workpiece into a rectangular hole.
Provides uniform alignment between a robot held component and contact
surface of a sub-assembly. This is useful for flexible machine loading, hotplate
welding, and spin welding applications.
Phase Match Insert
Insertion that is preceded by phase matching, such as key insertion
and spline insertion for a car transmission.
Typically, an insertion function requires that the positioning error
of the approach position is less than the chamfer amount. In certain insertion
applications, there may not be a chamfer or the position error may exceed
the chamfer amount. Search function is designed to help in such application
by minimizing the position and orientation error of the approach position
prior to an insertion operation.
Contouring Function traces the surface of a workpiece while applying
a constant force. Used with a tool such as a grinder, this function can perform
polishing and grinding. In general, if the workpiece to be machined is heavy
or large, the workpiece is secured onto a table and a grinder is attached
to the robot. If the workpiece to be machined is small compared with a tool,
the tool is secured onto a table, and the robot holds the workpiece. In either
case, the operation is performed while a set force is applied.
Bulit-in force sensor diagnosis instructions are used to verify that
a force sensor is in good working condition. Diagnostics provide sensor data
and alarms to indicate if a sensor is working properly. Most FANUC America
Force Sensors have an IP67 rating and can be used on a variety of robot models
such as the LR
Mate 200iC, M-10iA, M-20iA, M-710iC, and R-2000iB.
Force Sensing (Video)
Several software features coordinate with force sensing to determine
force control performance. Teach Pendant Program Auto Generation monitors
the edges of the workpiece in the contouring process with force control, and
automatically generates a teach pendant program to play back the monitored
edges. It is useful for operations where accurate edges are necessary such
as deburring a processed workpiece. As the grinder’s rotation speed
is constant, it tends to remove more material when the travel speed is low
than when it is high. In order to address this problem, this function automatically
reduces the push force when the travel speed is low. It is useful in cases
such as when the tool is stuck or the robot reverses travel direction.
Real time force sensor data display is a clear indication of performance
impact for force control parameters adjustment. This operation dramatically
reduces teaching time and provides instantaneous visual feedback for production
runs making possible issues easy to diagnose.
FANUC robots use integrated (or built-in) iRVision® for part location and evaluation. iRVision® is Integrated Robot Machine Vision
which is the integration of a camera interface built into the robot controller.
One or more cameras can be attached to the robot, or they can be in a remote
location. In traditional processes, if you want the robot to manipulate every
workpiece in the same way, you need to place every workpiece at exactly the
same position. iRVision® is a visual
sensor system designed to eliminate such restrictions. iRVision®
measures the position of each workpiece by using cameras, and it adjusts the
robot motion so that the robot can manipulate the workpiece in the same way
as programmed even if the position of the workpiece is different from the
workpiece position set when the robot program was taught. All of the application-specific
tools developed to simplify the use of the camera as a guidance, identification,
or inspection tool are integrated with the robot.
Handles multiple parts at one time.
Reduces floor space.
Makes part changeovers a breeze.
Identifies parts in multiple orientations.
Locates parts in 2D or 3D.
Error proofs the parts as they enter assembly, as well as
the assembly itself.
Reduces or eliminates fixturing costs.
As discussed in Using Robotics to go from CAD to Path, off-line programming
can be done initially to set up the workcell. FANUC America' off-line programming
software, ROBOGUIDE®, can play an important role in the development of
your application. This creation method offers maximum cell up-time when the
mathematical model of the cell is similar to the actual cell. ROBOGUIDE uses
3D models of actual tooling, robots, and parts in your workcell. If you use
good setup principals to set up the off-line robot system, the workcell will
prove accurate which saves time and money. After your program is created,
you can use program transfer tools to transfer the program to other robots
M-1iA Force Sensing with Vision
A FANUC M-1iA robot performs gear
assembly using 2D iRVision and Force Sensing.
With 2D iRVision, the robot locates two
different gear models. The robot then selects the appropriate tool to pick
the particular gear needed to start the assembly. The robot moves to a fixture
equipped with an FS-15iA force sensor and
assembles the gear onto a shaft. Then the robot changes grippers to pick and
assemble the other gear onto a shaft using face match. The flexibility, speed,
and accuracy of the M-1iA allows for precision
gear placement. The 2D iRVison system allows
the robot to locate gears of different sizes. The capabilities of the FS-15iA allow for precision force measurement for proper
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