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Technology Review TRJ Absolute Encoder
with Trapezoidal Signals
Trapezoid signal feedback technology addresses industries need for a small, low cost, absolute feedback device for high volume applications. The development, which has been made possible by the evolution of the current day Digital Signal Processors, utilizes a simple mechanical design to generate trapezoid waveforms. A representation of the design can be thought of as a large rectangular slot moving from right to left across a slit. The resultant signal defines the path The uniqueness behind the technology is the innovative method for sensing position and the fact that high resolution can be achieved with a simple mechanical structure. Where exiting technology looks for a sharp edge to signal a change of state, here we are looking at a change of area. The specific area is the area between the slot and the slit. See figure 1. This approach, with the aid of a DSP, interprets changes in the area, and then calculates the direction resulting in an absolute position. With this approach, excellent position control is achieved without the need for the mechanical tolerances required in current encoder technology. The operation principle of the technology offers a savings in computation steps. The stages to convert a 2-phase trapezoid input to a linear output are two simple steps. First, one of four quadrants are identified. Depending on the quadrant, a value of each phase plus a constant is added or subtracted. Sinusoidal signals require division of a variable and a look up table taking more computation time and resources than trapezoidal signals that require only addition and subtraction. The technology eliminates the worry of offset, gain, and phasing. By determining the maximum and minimum values of the analog trapezoid signal, the offset, gain, and phasing are automatically corrected. This is accomplished by the conversion of the multiphase signal to a single saw tooth signal that increases linearly from 0 at the start of the cycle to a specific maximum at the end of the cycle. This requirement implies that the amplitude and offset of the signals are standardized as part of the signal-processing algorithm. To allow for variation in the light strength of LED’s, advancements in algorithms to calculate correction tables have been made. The resultant is a high-resolution absolute encoder using low-resolution disks or scales as well as a greatly simplified mechanical configuration. This approach is equally useful with optical, capacitive, magnetic, and variable reluctance sensors. Signals can be generated that are compatible with most communication formats used in factory automation or other applications, including quadrature encoder output. Sequence of positions of Figure 1 1. In the first position the signal is a maximum 2. The signal remains a maximum until the edge of the slot reaches the right edge of the slit. 3. With ½ of the slit exposed, the signal is ½ maximum. 4. When the edge of the slot reaches the left edge of the slit, the signal is reduced to zero. 5. When the slit is centered between the slots the signal is zero. 6. The signal remains zero until the next slot reaches the right edge of the slit. 7. When the edge of the next slot reaches the left edge of the slit, the signal is ½ the maximum value and is increasing. 8. When the edge of the next slot reaches the left edge of the slit, the signal is again maximum. The product is currently in test in the robotic field. Rotary feedbacks are being tested on the wrist, hand, arm etc while a linear version if the technology is located on the transverse carriage. Back to Market Research
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