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Technical Brief

Design of Stabilizing Arm Mechanisms for Carrying and Positioning Loads

[+] Author and Article Information
Jeffrey Ackerman

School of Mechanical Engineering,
Purdue University,
585 Purdue Mall,
West Lafayette, IN 47906
e-mail: ackermaj@purdue.edu

Justin Seipel

Mem. ASME
School of Mechanical Engineering,
Purdue University,
585 Purdue Mall,
West Lafayette, IN 47906
e-mail: jseipel@purdue.edu

1Corresponding author.

Contributed by the Design Automation Committee of ASME for publication in the JOURNAL OF MECHANICAL DESIGN. Manuscript received June 2, 2014; final manuscript received June 28, 2015; published online August 10, 2015. Assoc. Editor: Matthew B. Parkinson.

J. Mech. Des 137(10), 104501 (Aug 10, 2015) (5 pages) Paper No: MD-14-1316; doi: 10.1115/1.4030987 History: Received June 02, 2014

Stabilizing arm mechanisms are used to support and position a load with minimal force from the user. Further, stabilizing arm mechanisms enable operators to stabilize the motion of the load while walking or running over variable terrain. Although existing stabilizing arm mechanisms have reached fairly broad adoption over a range of applications, it remains unknown exactly how the spring properties and geometric parameters of the mechanism enable its overall performance. We developed a simplified model to analyze the vertical dynamics of stabilizing arms to determine how the spring properties and mechanism geometry affect the natural frequency of the load mass, the range of load masses that can be supported, and the equilibrium position of the load mass. We found that decreasing the unstretched spring free length is the most effective way to minimize the natural frequency; the spring lever arm can be used to adjust for a desired load mass range, and the linkage length can be used to adjust the range of motion of the stabilizing arm. The spring stiffness should be selected based on the other parameters. This work provides a systematic design study of how the parameters of a stabilizing arm mechanism affect its behavior and fundamental design principles that could be used to improve existing mechanisms, and enable the design of new mechanisms.

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References

Figures

Grahic Jump Location
Fig. 1

The Steadicam® stabilizing arm (c) enables a camera and associated equipment to be positioned with minimal force from the operator [21] (a) and stabilizes the vertical motion of the camera during locomotion over flat ground and rough terrain (b)

Grahic Jump Location
Fig. 2

In a linear spring suspension system, the effective static spring deflection increases substantially as the natural frequency is minimized (a). A stabilizing arm mechanism is able to achieve natural frequencies between 0.2 Hz and 1.2 Hz with relatively small static spring deflections below 0.0762 m, (b) when the load mass was varied from 1.81 kg to 13.6 kg with the highest forearm lift adjustment value (a2 = 0.0394 m).

Grahic Jump Location
Fig. 3

Increasing the spring stiffness k increases the range of load mass that can be supported (a), but does not affect the relationship between the natural frequency of the mechanism and the static deflection of the load mass (b) (L = 0.2032 m, l0 = L − 0.0381 m, a2 = 0.0394 m). The lift adjustment a2 provides a useful means to change the equilibrium position and to adjust a stabilizing arm for different load masses (c), but it is best to minimize the lift adjustment a2 to minimize the natural frequency of the mechanism (d) (L = 0.2032 m, l0 = L − 0.0381 m, k = 11,733 N/m, a1 = a2 + 0.00635 m). Shorter arm linkage lengths L are able to support larger load masses (e) compared to longer arm linkage lengths, but increase the natural frequency of the mechanism (f) (l0 = L − 0.0381 m, a2 = 0.0394 m, a1 = a2 + 0.00635 m, k = 11,733 N/m). Decreasing the spring free length l0 enables the mechanism to support larger load masses (g) and significantly reduces the natural frequency of the mechanism (h) (L = 0.203 m, a2 = 0.0394 m, k = 11,733 N/m).

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