Kappasense Technology

1.1 Linear Encoders Technology

KappaSense’s linear capacitive encoder includes a scale and a read-head that interact as a variable capacitor. The scale is a thin printed circuit strip on which a transmitter periodic pattern is printed. The read-head is also a printed circuit substrate on which a receiver pattern is printed. A typical read-head has a small profile including the processing electronics, and provides absolute measurement outputs. Sensing is achieved by the interaction between the read-head and, resulting in the averaging of multiple transmitter periods. The averaging provides a high signal to noise ratio, allows mechanical mounting-error tolerance, and significant insensitivity to scale contamination.

The transmitter receiver mechanism is implemented in a dual track configuration, the “fine” track and the “coarse” track. This dual track system enables inherent absolute positioning measurement without the need for additional mechanisms and sensing devices.

 

The Capacitive Linear Encoder features several advantages in comparison with the traditional encoder technologies:

  • Scalability of size, easiness of customization, allows best fit to customer needs
  • Insensitivity to magnetic fields, thus the capacitive encoder is fully operational under strong magnetic fields.
  • The Capacitive Linear Encoder is significantly insensitive to deposited dust particles, due to the averaging over a large interaction area. The effect of both dust and moisture deposition, is further diluted due to the increased air gap supported. Thus maintenance is significantly easier and related costs minimal.
  • Holistic implementation provides extended resilience to tilt and eccentricity misalignments, thus the mechanical installation requirements for an Electric Linear Encoder are much less demanding. The tolerances allowed are significantly higher; usually installation is done by simply using a dual sided glue tape.
  • Significantly higher tolerances in dynamic deviations of the moving arm on non measured axes, up to ten times in comparison to optical solutions.

1.2 Capacitive Encoder Linear Implementations

 The capacitive technology has several possible implementations:

  • Passive Read Head
  • Passive Scale
  • Active All (Scale & Read Head)

KappaSense together with the customer selects the most suitable implementation for each case, depending on specific needs, best cost performance ratio and customer’s expectations

1.2.1 Passive Read Head

This unique implementation requires no cable feed for the moving Read Head which is completely passive, thus eliminating the need for cumbersome and costly harnesses. The main characteristics of this implementation

  • Absolute or Incremental Reading
  • High tolerance to assembly and dynamic misalignments in Z axis
  • Current Lengths of up to 1 m
  • Support of Multiple Read Head per scale

1.2.2 Passive Scale

In this implementation the scale is passive and only the read head has signal feeds and is powered. This is the most common implementations for traditional encoders. The main capabilities of this implementation:

  • Absolute or Incremental Reading
  • High tolerance to assembly and dynamic misalignments in all axes

1.2.3 Active All

In this implementation both the scale and the read head have signal feeds and are powered. This is the original and most common implementation, and is able to support highest range of dynamic and static mechanical misalignments.
The main capabilities of this implementation:

  • Absolute or Incremental Reading
  • Highest tolerance to assembly and dynamic misalignments in all axes
  • Support of Multiple Read Head per scale

1.3 Common Applications for Capacitive Linear Encoders

  • Semiconductors Industry: Wafer Handling, Lithography, clean room equipment
  • PCB manufacturing
  • Motor Feedback systems
  • Medical Equipment: CT, MRI, X-Ray machines, OR & moving tables.
  • LCD and Plasma screen manufacturing
  • Machine Builders and Robotics

2 Capacitive Rotary Encoders

The Capacitive Rotary Encoder can be implemented using either of two topologies: “3 plate” and “2 plate”, both include a space/time modulated electric field inside a shielded volume. The total field is integrated and converted into a signal current which is processed by on board electronics to provide DC output signals proportional to the sine and cosine of the rotation angle. In the 3 plate topology a dielectric rotor modulates the field between stationary transmitter and receiver plates. In the 2 plate topology, shown in Figure 1b, the field is confined between a stationary transmitter/receiver plate and a conductively patterned rotor.

The transmitter receiver mechanism is implemented in a dual track configuration, the “fine” track and the “coarse” track. This dual track system enables absolute angular positioning measurement without the need for additional mechanisms and sensing devices.
Many of the advantages of the Capacitive Encoder result from its “holistic” rotor: unlike in other encoders, the whole area of the Capacitive Encoder rotor participates in signal generation, i.e., multiple spatial periods are integrated.

2.1 Rotary Encoder Implementations

 The capacitive technology has being implemented in several models:

  • Medium Size 3- plate Encoders, between 60 and 300 mmm OD
  • Large bore 3-plate encoders, from 300 mm and up to 2.5 m and more
  • 2- plate encoders, for application where low heights of a few millimeters are required.

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