Force Control Application Implementation Plan

I. Touchscreen Function Detection

1.1 Requirements Analysis

• Functional requirement: The robot arm carries a writing pen and draws patterns such as straight lines or circles on the touchscreen at a drawing speed of 50 mm/s.

• Safety requirement: The maximum force between the writing pen and the touchscreen must not exceed 1.5 N to ensure the screen is not damaged.

• Force control accuracy requirement: While realizing pattern drawing and ensuring screen safety, the force between the pen and the screen needs to be maintained at 1 ± 0.5 N.

Tip

The incoming angle of the touchscreen (tilted between 30–60°) is inconsistent.

1.2 Solution

• Overall approach: The robot arm carries a writing pen and draws patterns such as straight lines or circles on the touchscreen. Force control maintains the force between the pen and the screen at 1 ± 0.5 N while ensuring a drawing speed of 50 mm/s.

• Main steps:

  1. The robot arm moves from the start position to a safe height above the touchscreen.
  2. The robot arm approaches the touchscreen at a low speed. When the pen contacts the screen and reaches the target force, pattern drawing begins.
  3. The robot arm draws patterns such as straight lines or circles on the touchscreen along the preset trajectory, keeping the force between the pen and the screen at 1 ± 0.5 N.
  4. After drawing is complete, the robot arm lifts the pen and returns to the start position.

• Touchscreen function detection video example:

1.3 Force Control Parameter Settings

• Force control reference coordinate system: The x-y plane of the coordinate system attitude is the screen plane, the z axis is perpendicular to the screen, and the origin of the coordinate system is arbitrary. It can be a moving coordinate system or a fixed coordinate system.

• Force control direction: Enable force control on the Z axis; disable it on other axes.

  enable = {false, false, true, false, false, false}

• Target force: The target force on the Z axis is 2 N; the target forces on other axes do not take effect and are recommended to be set to 0.

  goal_force = {0, 0.0, 2.0, 0.0, 0.0, 0.0}

• Reference trajectory: During the drawing stage, the reference trajectory is the straight line/arc set by the user. During the approach stage, the reference trajectory can be omitted, completing the approach entirely by force guidance, or a reference trajectory (MoveL) can be set to speed up the approach.

• Admittance parameters:

  M = {20, 20, 20, 10, 10, 10}
  D = {0, 0, 300, 0, 0, 0}
  K = {0, 0, 0, 0, 0, 0}

1.4 Potential Problems and Solutions:

• Excessive force during the approach stage

  • Cause: The approach speed is too fast, and the inertia of the robot arm causes the force to exceed the safety threshold.
  • Solution: Reduce the approach speed, set a reasonable approach trajectory, and use force guidance to approach.

• Large force fluctuations during drawing

  • Cause: The admittance parameters are set unreasonably, and the robot arm rigidity is too high.
  • Solution: Adjust the admittance parameters, increase the damping coefficient, and reduce the rigidity coefficient.

• Unstable force control caused by changes in screen angle

  • Cause: The coordinate system attitude does not match the actual attitude of the screen.
  • Solution: Use a vision system to detect the screen angle in real time and dynamically adjust the coordinate system attitude.

II. Fabric Ironing

2.1 Requirements Analysis

• Functional requirement: The robot arm carries an iron and moves along a preset trajectory on the fabric surface to realize fabric ironing.

• Force control requirement: The force between the iron and the fabric is maintained at 30 ± 5 N, ensuring the ironing effect while avoiding damage to the fabric.

• Movement speed requirement: During ironing, the robot arm movement speed is maintained at 100 mm/s to ensure uniform ironing.

2.2 Solution

• Overall approach: The robot arm carries an iron and moves along a preset trajectory on the fabric surface. Force control maintains the force between the iron and the fabric at 30 ± 5 N while ensuring a movement speed of 100 mm/s.

• Main steps:

  1. The robot arm moves from the start position to a safe height above the fabric.
  2. The robot arm approaches the fabric at a low speed. When the iron contacts the fabric and reaches the target force, ironing begins.
  3. The robot arm moves along the preset trajectory on the fabric surface, keeping the force between the iron and the fabric at 30 ± 5 N.
  4. After ironing is complete, the robot arm lifts the iron and returns to the start position.

• Fabric ironing video example:

2.3 Force Control Parameter Settings

• Force control reference coordinate system: The actual TCP or the command TCP output by force control.

• Force control direction: Enable force control on the Z axis; disable it on other axes.

  enable = {false, false, true, false, false, false}

• Target force: The target force on the Z axis is 30 N; the target forces on other axes do not take effect and are recommended to be set to 0.

  goal_force = {0, 0.0, 30, 0.0, 0.0, 0.0}

• Reference trajectory: The motion trajectory is the straight line/arc set by the user, and it must be ensured to be parallel to the fabric surface.

• Admittance parameters:

  M = {20, 20, 20, 10, 10, 10}
  D = {0, 0, 2000, 0, 0, 0}
  K = {0, 0, 0, 0, 0, 0}

2.4 Problems and Solutions

• There must be no stagnation during motion.

  • Cause: Stagnation causes the local temperature to become too high and damages the fabric.
  • Solution: Set a reasonable movement speed and avoid the robot arm staying on the fabric surface.

• Different fabric thicknesses require different forces.

  • Cause: Different fabric thicknesses require different ironing forces.
  • Solution: Adjust the target force according to the fabric thickness, and use a vision system to detect the fabric thickness.

III. Gear Meshing

3.1. Requirements Analysis

• Functional requirement: The robot arm carries a gear and realizes precise meshing with a fixed gear.

• Force control requirement: During gear meshing, the force is maintained at 5 ± 1 N to avoid damage to the gears.

• Accuracy requirement: The gear meshing accuracy reaches 0.1 mm to ensure the gears operate normally.

3.2. Solution

• Overall approach: The robot arm carries a gear and realizes precise meshing with a fixed gear through force control, ensuring the force during meshing is within 5 ± 1 N while ensuring meshing accuracy.

• Main steps:

  1. The robot arm moves from the start position to a safe height above the fixed gear.
  2. The robot arm approaches the fixed gear at a low speed. When the gear contacts and reaches the target force, meshing begins.
  3. The robot arm adjusts its attitude through force control to realize precise meshing of the gear.
  4. After meshing is complete, the robot arm maintains its attitude to complete the gear meshing operation.

• Gear meshing video example:

3.3 Force Control Parameter Settings

• Force control reference coordinate system: The TCP coordinate system, ensuring the coordinate system origin is at the gear center.

• Force control direction: Determined by the gear meshing direction, generally the X or Y axis.

• Target force: Determined by the gear size and material, generally 5 ± 1 N.

• Reference trajectory: The gear meshing trajectory, which must be aligned with the tooth slots of the fixed gear.

• Admittance parameters:

  M = {20, 20, 20, 10, 10, 10}
  D = {0, 0, 1000, 0, 0, 0}
  K = {0, 0, 0, 0, 0, 0}
  enable = {false, false, true, false, false, false}
  goal_force = {0, 0.0, 5, 0.0, 0.0, 0.0}

  • Admittance parameters (after adjustment):

    M = {20, 20, 20, 10, 10, 10}
    D = {0, 0, 2000, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}
    enable = {false, false, true, false, false, false}
    goal_force = {0, 0.0, 8, 0.0, 0.0, 0.0}

  • Admittance parameters (final):

    M = {20, 20, 20, 10, 10, 10}
    D = {2000, 2000, 2000, 1000, 1000, 1000}
    K = {0, 0, 0, 0, 0, 0}
    enable = {true, true, true, true, true, false}
    goal_force = {0, 0.0, 20, 0.0, 0.0, 0.0}

IV. USB Drive Automatic Insertion/Removal

4.1 Requirements Analysis

• Functional requirement: The robot arm carries a USB drive and realizes automatic insertion and removal with the computer's USB interface.

• Force control requirement: During insertion and removal, the force is maintained at 10 ± 2 N to avoid damage to the USB interface.

• Accuracy requirement: The USB interface alignment accuracy reaches 0.5 mm to ensure the USB drive is inserted correctly.

4.2 Solution

• Overall approach: The robot arm carries a USB drive and realizes automatic insertion and removal with the computer's USB interface through force control, ensuring the force during insertion and removal is within 10 ± 2 N while ensuring interface alignment accuracy.

• Main steps:

  1. The robot arm moves from the start position to a safe position in front of the computer's USB interface.
  2. The robot arm approaches the USB interface at a low speed. When the USB drive contacts the interface and reaches the target force, insertion begins.
  3. The robot arm adjusts its attitude through force control to realize precise insertion of the USB drive.
  4. After insertion is complete, the robot arm maintains its attitude to complete the USB drive insertion operation.
  5. During removal, the robot arm removes the USB drive at a low speed, keeping the force at 10 ± 2 N.

• USB drive automatic insertion/removal video example:

4.3 Force Control Parameter Settings:

• Force control reference coordinate system: The TCP coordinate system, ensuring the coordinate system origin is at the center of the USB drive.

• Force control direction:

  • Guide slot insertion stage: Correct the Rx and Ry directions of the USB drive through guide slot insertion.

  • Insertion stage: Normally enable force control in the X, Y, and Z directions. After on-site verification, it was found that the USB interface has a physical structure error, so the USB port needs to be rotated downward, and giving a negative-direction force on Rx helps insert it to the bottom.

• Target force:

  • Guide slot stage, TCP-Z, target force 1 N in the direction; other axes are recommended to be set to 0.

  • Insertion stage, TCP-Z, target force 0.5 N in the Rx direction; other axes are recommended to be set to 0.

• Admittance parameters:

  • Admittance parameters (guide slot stage):

    M = {20, 20, 20, 10, 10, 10}
    D = {0, 0, 1000, 1000, 1000, 0}
    K = {0, 0, 0, 0, 0, 0}

  • Admittance parameters (insertion stage):

    M = {20, 20, 20, 10, 10, 10}
    D = {1000, 1000, 1500, 1500, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

V. Waterproof Cover Installation

5.1. Requirements Analysis

• Functional requirement: The robot arm carries a waterproof cover and realizes precise installation on the device.

• Force control requirement: During installation, the force is maintained at 8 ± 2 N to avoid damage to the waterproof cover.

• Accuracy requirement: The waterproof cover installation accuracy reaches 0.2 mm to ensure the waterproof effect.

5.2 Solution

• Overall approach: The robot arm carries a waterproof cover and realizes precise installation on the device through force control, ensuring the force during installation is within 8 ± 2 N while ensuring installation accuracy.

• Main steps:

  1. The robot arm moves from the start position to a safe height above the device.
  2. The robot arm approaches the device at a low speed. When the waterproof cover contacts the device and reaches the target force, installation begins.
  3. The robot arm adjusts its attitude through force control to realize precise installation of the waterproof cover.
  4. After installation is complete, the robot arm maintains its attitude to complete the waterproof cover installation operation.

• Waterproof cover installation video example:

5.3 Force Control Parameter Settings

• Force control reference coordinate system: The TCP coordinate system, ensuring the coordinate system origin is at the center of the waterproof cover.

• Force control direction:

  • Approach stage: Enable force control on TCP-X and TCP-Y; disable it on other axes.

  • Pressing-down stage: Enable force control on TCP-X, TCP-Y, and TCP-Z; disable it on other axes.

• Target force:

  • Approach stage: Target force 2 N in the TCP-X and TCP-Y directions; the target forces on other axes do not take effect and are recommended to be set to 0.

  • Pressing-down stage: Target force 0 N in the TCP-X and TCP-Y directions and 5 N in the TCP-Z direction; the target forces on other axes do not take effect and are recommended to be set to 0.

• Admittance parameters:

  • Admittance parameters (approach stage):

    M = {20, 20, 20, 10, 10, 10}
    D = {500, 500, 0, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

  • Admittance parameters (pressing-down stage):

    M = {20, 20, 20, 10, 10, 10}
    D = {500, 500, 800, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

VI. Knob Installation

6.1. Requirements Analysis

• Functional requirement: The robot arm carries a knob and realizes precise installation on the device.

• Force control requirement: During installation, the force is maintained at 10 ± 2 N to avoid damage to the knob.

• Accuracy requirement: The knob installation accuracy reaches 0.1 mm to ensure the knob operates normally.

6.2. Solution

• Overall approach: The robot arm carries a knob and realizes precise installation on the device through force control, ensuring the force during installation is within 10 ± 2 N while ensuring installation accuracy.

• Main steps:

  1. The robot arm moves from the start position to a safe height above the device.
  2. The robot arm approaches the device at a low speed. When the knob contacts the device and reaches the target force, installation begins.
  3. The robot arm adjusts its attitude through force control to realize precise installation of the knob.
  4. After installation is complete, the robot arm maintains its attitude to complete the knob installation operation.

• Knob installation video example:

6.3 Force Control Parameter Settings

• Force control reference coordinate system: The TCP coordinate system, ensuring the coordinate system origin is at the center of the knob.

• Force control direction:

  • Outer ring alignment and hole search: Enable force control on TCP-Z; disable it on other axes.

  • Inner cylinder alignment and hole search: Enable force control on TCP-Z; disable it on other axes.

• Target force:

  • Outer ring alignment and hole search: Target force 8 N in the TCP-Z direction; the target forces on other axes do not take effect and are recommended to be set to 0.

  • Inner cylinder alignment and hole search: Target force 5 N in the TCP-Z direction; the target forces on other axes do not take effect and are recommended to be set to 0.

• Admittance parameters:

  • Admittance parameters (outer ring alignment):

    M = {20, 20, 20, 10, 10, 10}
    D = {500, 500, 0, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

  • Admittance parameters (inner cylinder alignment):

    M = {20, 20, 20, 10, 10, 10}
    D = {500, 500, 800, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

VII. Hinge Installation

7.1 Requirements Analysis

• Functional requirement: The robot arm carries a hinge and realizes precise installation on the device.

• Force control requirement: During installation, the force is maintained at 8 ± 2 N to avoid damage to the hinge.

• Accuracy requirement: The hinge installation accuracy reaches 0.1 mm to ensure the hinge operates normally.

7.2. Solution

• Overall approach: The robot arm carries a hinge and realizes precise installation on the device through force control, ensuring the force during installation is within 8 ± 2 N while ensuring installation accuracy.

• Main steps:

  1. The robot arm moves from the start position to a safe height above the device.
  2. The robot arm approaches the device at a low speed. When the hinge contacts the device and reaches the target force, installation begins.
  3. The robot arm adjusts its attitude through force control to realize precise installation of the hinge.
  4. After installation is complete, the robot arm maintains its attitude to complete the hinge installation operation.

• Hinge installation video example:

7.3 Force Control Parameter Settings

Force control reference coordinate system: The TCP coordinate system, ensuring the coordinate system origin is at the center of the hinge.

• Force control direction:

  • Hinge screwing-in: Enable force control on TCP-Z; disable it on other axes.

  • Hinge pressing-down: Enable force control on TCP-Z; disable it on other axes.

• Target force:

  • Hinge screwing-in: Target force 8 N in the TCP-Z direction; the target forces on other axes do not take effect and are recommended to be set to 0.

  • Hinge pressing-down: Target force 5 N in the TCP-Z direction; the target forces on other axes do not take effect and are recommended to be set to 0.

• Admittance parameters

  • Admittance parameters (hinge screwing-in):

    M = {20, 20, 20, 10, 10, 10}
    D = {0, 0, 1000, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

  • Admittance parameters (hinge pressing-down):

    M = {20, 20, 20, 10, 10, 10}
    D = {0, 0, 1000, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

VIII. Driver Board Installation

8.1 Requirements Analysis

• Functional requirement: The robot arm carries a driver board and realizes precise installation on the device.

• Force control requirement: During installation, the force is maintained at 5 ± 1 N to avoid damage to the driver board.

• Accuracy requirement: The driver board installation accuracy reaches 0.1 mm to ensure the driver board works normally.

8.2 Solution

• Overall approach: The robot arm carries a driver board and realizes precise installation on the device through force control, ensuring the force during installation is within 5 ± 1 N while ensuring installation accuracy.

• Main steps:

  1. The robot arm moves from the start position to a safe height above the device.
  2. The robot arm approaches the device at a low speed. When the driver board contacts the device and reaches the target force, installation begins.
  3. The robot arm adjusts its attitude through force control to realize precise installation of the driver board.
  4. After installation is complete, the robot arm maintains its attitude to complete the driver board installation operation.

• Driver board installation video example:

8.3 Force Control Parameter Settings:

• Force control reference coordinate system: The TCP coordinate system, ensuring the coordinate system origin is at the center of the driver board.

• Force control direction:

  • Position confirmation: Enable force control on TCP-X and Rz; disable it on other axes.

  • Pressing down: Enable force control on TCP-Z; disable it on other axes.

  • Slot: Enable force control on TCP-X; disable it on other axes.

• Target force:

  • Position confirmation: Target force 2 N in the TCP-X direction; the target forces on other axes do not take effect and are recommended to be set to 0.

  • Pressing down: Target force 5 N in the TCP-Z direction; the target forces on other axes do not take effect and are recommended to be set to 0.

  • Slot: Target force 8 N in the TCP-X direction; the target forces on other axes do not take effect and are recommended to be set to 0.

• Admittance parameters

  • Admittance parameters (position confirmation):

    M = {20, 20, 20, 10, 10, 10}
    D = {1000, 0, 0, 0, 0, 500}
    K = {0, 0, 0, 0, 0, 0}

  • Admittance parameters (pressing down):

    M = {20, 20, 20, 10, 10, 10}
    D = {0, 0, 1000, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

  • Admittance parameters (slot):

    M = {20, 20, 20, 10, 10, 10}
    D = {1000, 0, 0, 0, 0, 0}
    K = {0, 0, 0, 0, 0, 0}

IX. Multi-Stage Force Control

9.1. Requirements Analysis

• Functional requirement: The robot arm realizes multi-stage force control to adapt to different operation requirements.

• Force control requirement: The force at different stages is maintained at the set value, with an error not exceeding 0.5 N.

• Accuracy requirement: The multi-stage force control switching accuracy reaches 0.1 s to ensure smooth operation.

9.2. Solution

• Overall approach: The robot arm realizes force control at different operation stages through multi-stage force control, ensuring the force at each stage is at the set value while ensuring the smoothness of force control switching.

• Main steps:

  1. The robot arm moves from the start position to the operation position.
  2. The robot arm sequentially executes different operation stages according to the preset multi-stage force control parameters.
  3. After each stage ends, the robot arm automatically switches to the next stage's force control parameters.
  4. After all stages are complete, the robot arm returns to the start position.

• Multi-stage force control video example:

9.3 Force Control Parameter Settings

• Force control reference coordinate system: The TCP coordinate system, ensuring the coordinate system origin is at the center of the operation tool.

• Force control direction: Enable force control on TCP-Z; disable it on other axes.

  enable = {false, false, true, false, false, false}

• Target force:

  • First stage: Target force 6 N in the TCP-Z direction.

  • Second stage: Target force 1 N in the TCP-Z direction.

  • Third stage: Target force 6 N in the TCP-Z direction.

• Reference trajectory: The multi-stage trajectory set according to the operation requirements, ensuring the trajectory is parallel to the operation surface.

• Admittance parameters:

  M = {20, 20, 20, 10, 10, 10}
  D = {0, 0, 1000, 0, 0, 0}
  K = {0, 0, 0, 0, 0, 0}

X. Charging Interface Insertion/Removal

10.1 Requirements Analysis

• Functional requirement: The robot arm carries a charging interface and realizes automatic insertion and removal with the device.

• Force control requirement: During insertion and removal, the force is maintained at 15 ± 3 N to avoid damage to the charging interface.

• Accuracy requirement: The charging interface alignment accuracy reaches 0.5 mm to ensure normal charging.

10.2. Solution

• Overall approach: The robot arm carries a charging interface and realizes automatic insertion and removal with the device through force control, ensuring the force during insertion and removal is within 15 ± 3 N while ensuring interface alignment accuracy.

• Main steps:

  1. The robot arm moves from the start position to a safe position in front of the device's charging interface.
  2. The robot arm approaches the charging interface at a low speed. When the interface contacts and reaches the target force, insertion begins.
  3. The robot arm adjusts its attitude through force control to realize precise insertion of the charging interface.
  4. After insertion is complete, the robot arm maintains its attitude to complete the charging interface insertion operation.
  5. During removal, the robot arm removes the charging interface at a low speed, keeping the force at 15 ± 3 N.

• Charging interface insertion/removal video example:

10.3 Force Control Parameter Settings

• Force control reference coordinate system: The TCP coordinate system, ensuring the coordinate system origin is at the center of the charging interface.

• Force control direction:

  • Hole search: Enable force control on TCP-Z; disable it on other axes.

  • Insertion/removal: Enable force control on all directions except the Rz direction.

• Target force:

  • Hole search: Target force 40 N in the TCP-Z direction.

  • Insertion/removal: The target force in each direction is set according to the actual situation.

• Admittance parameters

  • Admittance parameters (hole search):

    M = {20, 20, 20, 10, 10, 10}
    D = {1000.0, 1000.0, 2500.0, 100.0, 100.0, 50}
    K = {6000.0, 6000.0, 1000.0, 0.0, 0.0, 0.0}

  • Admittance parameters (insertion/removal):

    M = {20, 20, 20, 10, 10, 10}
    D = {600.0, 600.0, 3500.0, 200.0, 200.0, 200.0}
    K = {10.0, 10.0, 4000.0, 200.0, 200.0, 200.0}

10.4 Problems and Solutions:

• Difficult interface alignment

  • Cause: The charging interface position accuracy requirement is high, and the robot arm positioning error is relatively large.
  • Solution: Use a vision system to assist positioning and improve the robot arm positioning accuracy.

• Excessive insertion/removal force

  • Cause: The robot arm inertia causes the force to exceed the safety threshold.
  • Solution: Reduce the insertion/removal speed and set reasonable force control parameters.

• Interface damage

  • Cause: The force during insertion/removal is too large or the attitude is incorrect.
  • Solution: Optimize the force control parameters to ensure the force during insertion/removal is within the safe range.