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Ultrasound Based Load Cell for Accurate Assembly

IP.com Disclosure Number: IPCOM000248983D
Publication Date: 2017-Jan-25
Document File: 3 page(s) / 67K

Publishing Venue

The IP.com Prior Art Database

Related People

ShunChong Li: AUTHOR [+3]

Abstract

In accurate assembly, small position uncertainties of robot end effector might lead to large force and potentially break the fragile parts. The uncertainties can be compensated for by introducing a load cell – a type of force sensor that is used to create an electrical signal whose magnitude is proportional to the measured force. Traditional load cell is based on strain gauge which measures the deformation as a change in electrical resistance and hence the applied force. The drawbacks of this type of load cell are short lifetime and low sensitivity to detect small force. In this disclosure, we present a new type of load cell based on the acoustic method filled in the previous patent. It can measure applied force and provide a proportional output signal. All the key components such as transducer, receiver, contacting parts and signal processing circuit are designed well and integrated in a closure housing as a module which makes it easy to substitute traditional stain gauge load cell for accurate assembly.

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1

Ultrasound Based Load Cell for Accurate Assembly

1 BACKGROUND In accurate assembly, small position uncertainties of robot end effector might lead to large force and potentially break the fragile parts. The uncertainties can be compensated for by introducing a load cell – a type of force sensor that is used to create an electrical signal whose magnitude is proportional to the measured force.

Traditional load cell is based on strain gauge which measures the deformation as a change in electrical resistance and hence the applied force. The drawbacks of this type of load cell are short lifetime and low sensitivity to detect small force.

In this disclosure, we present a new type of load cell based on the acoustic method filled in the previous patent. It can measure applied force and provide a proportional output signal. All the key components such as transducer, receiver, contacting parts and signal processing circuit are designed well and integrated in a closure housing as a module which makes it easy to substitute traditional stain gauge load cell for accurate assembly.

2 THE IDEA The basic idea of this disclosure is to use ultrasound wave transfer characteristic in a practical contacting interface with certain roughness. The transmission energy is proportional to the force applied on the interface.

Figure 1. Ultrasound transmission in an interface. I is incident wave, T is transmitted and R is reflected.

As illustrated in Figure 1(a), when an ultrasonic wave is incident into the interface between two perfectly bonded materials, the transmission coefficient T is

= 1 − − +

2

Where z is the acoustic impedance and the subscripts refer to the materials on either side of the interface. Assuming the materials are the same on the both sides, the transmitted wave has the same amplitude of the incident wave.

For a practical interf...