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From Transportation to Manipulation: Enabling Grasping in Magnetic Robotics

Lara Bergmann, Noah Greis, Cedric Grothues, Lisa-Marie Weigelt, Klaus Neumann

arXiv:2609.12883v1cs.RO

TL;DR

Industrial MagLev systems have largely focused on transportation, leaving grasping and manipulation underused. The Gripper MagBot couples a manipulator and gripper to three movers; their wrenches contain payload-dependent patterns that support payload estimation.

  • Problem

    Industrial MagLev applications largely focus on transportation, while their manipulation capabilities remain underused.

    Source: §I · p. 1

  • Method

    The Gripper MagBot couples three MagLev movers to a parallel 6-DoF manipulator and 1-DoF gripper, with autonomous docking and an inverse kinematics controller.

    Source: §I · p. 1

  • Results

    Mover wrenches contain payload-dependent patterns, enabling payload estimation solely from the movers’ wrenches.

    Source: §VIII · p. 8

  • Takeaways & Limitations

    The docking-compatible design allows MagLev systems to equip themselves with different manipulation capabilities using MagBots.

    Source: §VIII · p. 8

    XPlanar constraints limited tested γ-axis motion to ±10° and prevented measurement of single-track α-axis accuracy and repeatability.

    Source: A. Positioning Accuracy and… · p. 5

Abstract

from arXiv · show

Magnetic levitation (MagLev) systems have great potential for application in high-mix, low-volume manufacturing due to their scalability and flexibility, enabling highly reconfigurable in-machine material flow. However, their manipulation capabilities remain largely unexploited, as current applications almost exclusively focus on transportation. To enable grasping and manipulation directly on MagLev systems without requiring additional costly handling equipment, such as industrial robot arms, we present the Gripper MagBot, a low-cost parallel 6-DoF manipulator with an integrated 1-DoF gripper that mechanically couples three MagLev movers. The Gripper MagBot supports two operating configurations: a default mode and a single-track mode, selectable depending on the required stability and workspace footprint. To reconfigure a machine, the MagBot can be autonomously dropped off and picked up using a docking station. We showcase pick-and-place examples in simulation, as well as with the real Gripper MagBot using our inverse kinematics controller. CAD files, assembly instructions, a component list, and videos are available at https://sites.google.com/view/gripper-magbot.

I. INTRODUCTION

Industrial MagLev systems offer reconfigurable material flow, but their manipulation capabilities remain underused because single movers have restricted workspaces and cannot grasp. The paper introduces a three-mover Gripper MagBot and contributes docking, inverse-kinematics, simulation, and performance-evaluation work.

I. INTRODUCTION

  • Single MagLev movers have restricted workspaces and lack grasping ability, leaving industrial systems’ manipulation capabilities largely unexploited.The earlier two-mover 6D-Platform MagBot increased reachable workspace and payload but still lacked grasping.Source: §I · p. 1
  • The Gripper MagBot is a low-cost parallel 6-DoF manipulator with a 1-DoF gripper mechanically coupled to three MagLev movers.It is designed to enable grasping without additional expensive handling equipment such as robot arms.Source: §I · p. 1
  • The Gripper MagBot is compatible with the 6D-Platform MagBot docking station for autonomous machine reconfiguration.Movers can pick up or drop off the MagBot.Source: §I · p. 1
  • The paper contributes an inverse kinematics controller for the Gripper MagBot.Source: §I · p. 1
  • The paper contributes a physics-based Gripper MagBot simulation integrated into MagBotSim.Source: §I · p. 1
  • The paper investigates gripper performance metrics and evaluates the Gripper MagBot’s applicability.Source: §I · p. 1

II. RELATED WORK

The related-work discussion places the Gripper MagBot at the intersection of industrial MagLev manipulation and reconfigurable robotics. Its design balances compactness, self-sufficiency, docking-based reconfiguration, compatibility, affordability, and robustness.

II. RELATED WORK

  • Unlike prior industrial MagLev work focused on mover control or trajectory planning, the Gripper MagBot targets object manipulation and combines in-machine transportation with manipulation.The paper identifies its earlier 6D-Platform MagBot as the closest predecessor, extending that line with grasping while retaining compatibility.Source: §II · p. 2

III. DESIGN DECISIONS

  • Design decisions balance a small single-track footprint, no batteries or onboard actuation, docking-based reconfiguration, MagLev compatibility, affordability, and robustness.The MagBot uses 3D-printed components, weighs 1.775 kg, and costs about 400 USD.Source: §III · p. 2

A. 6-DoF Manipulator with 1-DoF Gripper

The Gripper MagBot mechanically converts the three movers’ motions into platform positioning, gripper rotation, and finger opening or closing. Its modified docking mechanism preserves compatibility while allowing movers to switch roles.

A. 6-DoF Manipulator with 1-DoF Gripper

  • Mover x- and y-axes position the platform, while mover γ-rotations drive gripper α/β rotation and finger motion through mechanical transmissions.The gear and belt mechanisms transmit and redirect rotation; coordinated opposite or same-direction rotations of movers 1 and 2 control α or β, respectively.Source: A. 6-DoF Manipulator with 1-DoF Gripper · pp. 2–3

B. Compatibility and Docking Mechanism

  • A second spring-loaded docking pin makes the mover attachment rotationally symmetric, enabling role switching while retaining compatibility with the 6D-Platform MagBot docking stations.Compatibility with the named MagLev systems requires only aligning the mover-side screw-hole positions with the mover design.Source: B. Compatibility and Docking Mechanism · p. 3

C. Single-Track Mode

The Gripper MagBot's single-track configuration trades stability for a narrower footprint, while its inverse-kinematics controller maps a desired gripper pose to mover commands. The controller also supports trajectory planning subject to geometric safety constraints.

C. Single-Track Mode

  • Single-track mode places the third mover below the platform, reducing y-direction footprint but providing less stability than default mode.It is intended mainly for narrow one- or two-tile paths or when a small y-direction footprint is required, not primarily for manipulation.Source: C. Single-Track Mode · p. 3

IV. INVERSE KINEMATICS CONTROLLER

  • The controller takes the desired end-effector pose and finger distance as input and outputs each mover’s required x- and y-positions and γ-rotation.Mover α- and β-rotations are set to 0°.Source: §IV · p. 3
  • The inverse-kinematics calculations derive platform position and mover spacing from the desired gripper pose, with the mover-3 distance sign set by operating mode.Relevant mechanical dimensions are taken from the CAD model.Source: §IV · p. 4
  • The controller can pair with trajectory planners that respect mover-distance limits and minimum gripper positions tied to platform z-height, preventing tile collisions or damage.Source: §IV · p. 4
  • Figure 5 contrasts simulated and real pick-and-place tasks, which differ slightly because of MagLev-system limitations.Source: Figure 5 · p. 4

V. PERFORMANCE METRICS

The performance metrics describe the Gripper MagBot's motion capabilities and workspace. Some workspace limits depend on the MagLev layout and mover-rotation support.

V. PERFORMANCE METRICS

  • Both operating modes reach a maximum velocity of 2 m/s and maximum acceleration of 10 m/s2.Source: §V · p. 4
  • The z-workspace maximum is 220.37 mm when the platform is at its maximum z-position and the gripper has α = 0.Source: §V · p. 4
  • The γ-workspace is mechanically unlimited, but achieving a full 360° gripper rotation depends on mover support; the lab tiles permit 360° turns only at specific positions.At other positions, the lab movers can rotate only ±10°.Source: §V · p. 4
  • The x- and y-workspace depends on the MagLev tile layout, while the z-workspace also depends on platform position and desired gripper α-rotation.Source: §V · p. 4

VI. SIMULATION

The authors integrated a Gripper MagBot model and its inverse-kinematics controller into MagBotSim. They demonstrated a simulated pick-and-place task and report that further simulation experiments remain future work.

VI. SIMULATION

  • A MuJoCo Gripper MagBot model and its inverse-kinematics controller are integrated into the open-source MagBotSim library.The library also includes the 6D-Platform MagBot model and is intended to facilitate MagBot motion-planning and manipulation development.Source: §VI · p. 4
  • 19.661 s was the completion time for one simulated pick-and-place run, corresponding to approximately 183 products per hour.The task rotated a cube to orient its white side upward and placed it on a different-height platform offset along the x-axis, requiring all MagBot DoFs.Source: §VI · p. 5
  • Further simulation experiments remain for future work.Source: §VI · p. 5

VII. EXPERIMENTS

Experiments used a Beckhoff XPlanar MagLev system, with the inverse-kinematics controller running on a TwinCAT 3 PLC. The authors calibrated mover gear ratios and set operating conditions for the two modes.

VII. EXPERIMENTS

  • Experiments used a Beckhoff XPlanar system with APM4330 movers and APS4322 tiles in a 4x3 grid, and a TwinCAT 3 PLC implementation of the controller.Source: §VII · p. 5
  • The estimated gear ratios were sm,1 = sm,2 = 0.9969 and sm,3 = −182.4376.The authors used VICON measurements and linear regression; mover 1 and 2 rotations were tested from 0° to 40°, while mover 3 was rotated in 360° steps from 0° to 1800°.Source: §VII · p. 5
  • Unless otherwise stated, mover flight altitude was 1 mm; default mode used low-level parameter set 0, while single-track mode used set 1 for mover α- and β-axes.Source: §VII · p. 5

A. Positioning Accuracy and Repeatability

The Gripper MagBot achieved sub-millimeter/sub-degree accuracy in most tested axes, but results varied by axis and operating mode. Default mode performed better than single-track mode on the simultaneous trajectories, especially the high-dynamics helix.

A. Positioning Accuracy and Repeatability

  • Sub-millimeter/sub-degree accuracy was achieved in all axes except y in single-track mode, α, and β.The XPlanar system prevented some measurements, including α accuracy and repeatability in single-track mode and β in single-track mode; its torque limits also constrained the measurable ranges.Source: A. Positioning Accuracy and… · p. 5
  • Fig. 6 compares set and VICON-measured gripper positions during simultaneous x, y, and z movements in both operating modes.The reported trajectories were a circular motion in x and y with sinusoidal z motion, and an extending-radius helix executed with high dynamics.Source: Figure 6 · p. 6, A. Positioning Accuracy and… · p. 6
  • Default mode produced better results than single-track mode on both simultaneous trajectories, with a particularly large difference for the high-dynamics helix.The helix results were worse than those for the circular x-y motion with sinusoidal z motion; mechanical play in y also contributed to helix errors.Source: A. Positioning Accuracy and… · p. 6

B. Control Parameters and Mode Switching

Single-track operation requires different low-level control parameters to avoid oscillation, while default mode is stabilized by its third mover. Mover wrenches also show payload-dependent patterns in both modes, with clearer separation in single-track mode.

B. Control Parameters and Mode Switching

  • Default mode does not oscillate with default control parameters because the third mover stabilizes the MagBot.When switching to single-track mode, the authors report that parameter set 1, originally tuned for the 6D-Platform MagBot, clearly reduces oscillations.Source: B. Control Parameters and Mode Switching · p. 6
  • Parameter set 1 eliminated observable single-track oscillation that appeared with parameter set 0 in gripper y-position and mover α-axis torque.The authors use parameter set 1 for α- and β-axes in single-track mode; it also keeps the MagBot stable with payload.Source: B. Control Parameters and Mode Switching · p. 6, Figure 7 · p. 6

C. Payloads and Mover Wrenches

  • Mover wrenches contain payload-dependent patterns in both modes, supporting payload estimation from the movers' wrenches alone.Measurements used payloads from 0 g to 70 g in 10 g increments; separate PCA models were used for each mode, and single-track projections were more clearly separated.Source: C. Payloads and Mover Wrenches · pp. 6–7
  • The PCA models emphasize x- and z-components in default mode and the z-component in single-track mode, which is particularly sensitive to payload there.Default-mode projections are often close together, making small weights more difficult to distinguish; the authors suggest investigating temperature dependency or water cooling because the system heated quickly.Source: C. Payloads and Mover Wrenches · p. 7

D. Reconfigurability

The Gripper MagBot can be autonomously picked up and dropped off to reconfigure the machine. Tests showed reliable operation across mover configurations, while docking-fork material choices affected the required reinforcement.

D. Reconfigurability

  • The tested docking arrangement used reinforced left and right forks and a PPA-CF center fork; PPA-CF alone was not suitable for all three stations.The authors report that PPA-CF forks bend slightly more than the PETG forks reinforced with stainless steel plates.Source: D. Reconfigurability · p. 7
  • After drop-off, the movers can perform any movement during the free-movement phase, demonstrating their interchangeability.The interchangeability is achieved through a modification to the component screwed onto the mover.Source: Figure 9 · p. 7, D. Reconfigurability · p. 7
  • The docking mechanism achieved 100% success rates for both pick-up and drop-off across 15 trials each.The trials covered five repetitions in each of three mover configurations, with movers changing positions during free movement after drop-off.Source: D. Reconfigurability · p. 7

E. Pick-and-Place Example

The real Gripper MagBot completed a cube pick-and-place, while the conclusion reports positioning performance, payload-estimation patterns, and remaining system constraints.

E. Pick-and-Place Example

  • The real system completed a 4+1-DoF cube pick-and-place in about 1.142 min (~52 products per hour), demonstrating successful grasping and placement.The task used x, y, z, α, and the fingers.Source: E. Pick-and-Place Example · pp. 7–8
  • On the real XPlanar, rotation constraints currently limit cube pickup and placement to one (x, y, z)-position.The system currently cannot perform a 180° MagBot rotation.Source: E. Pick-and-Place Example · p. 7

VIII. CONCLUSION AND FUTURE WORK

  • The inverse-kinematics controller achieved sub-millimeter/sub-degree positioning accuracy and repeatability in almost all axes across both modes, except y in single-track mode, α, and β.The authors identify β, in particular, as needing improvement.Source: §VIII · p. 8
  • Payload-dependent wrench patterns enabled payload estimation, although the relation may also depend on MagLev system temperature.The authors identify temperature dependence as a topic for future investigation.Source: §VIII · p. 8
  • The two modes differ in stability and workspace footprint, while shared docking enables autonomous reconfiguration for high-mix, low-volume manufacturing.The conclusion identifies high-mix, low-volume manufacturing as a suitable context for MagBots.Source: §VIII · p. 8, E. Pick-and-Place Example · p. 8
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