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Utilizing Force Sensors in Your Robotic Applications

Force sensing and robotic vision techniques have been introduced into industry as an added enhancement to the proven effectiveness of robots in manufacturing.

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

  • Flexible part feeding


At FANUC Robotics, 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 operation.


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 Insert

    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.

  • Face Match

    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.

  • Search Function

    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

    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 Robotics 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)


Additional Software Features used With Force Sensing

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.


iRVision®

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.

iRVision®:

  • 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.

  • Increases throughput.

  • Reduces or eliminates fixturing costs.

Off-Line Programming

Off-Line Programming


Off-Line Programming

As discussed in Using Robotics to go from CAD to Path, off-line programming can be done initially to set up the workcell. FANUC Robotics' 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 without touchup.





M-1iA Force Sensing with Vision Example (Video)


M-1iA Force Sensing Application

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 gear assembly.


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