Patent DE-19900581-A1 (DE)
Title: Non-contact measurement of yarn speed or running length uses grid rods in a structured electrode array to give signals from the yarn electrostatic charge to be processed to display the speed/length values
Inventor: SCHAEFER WOLFGANG
IPC: G01P3/66
Filed: 1999-01-09
Abstract: To measure the movement of a yarn, without contact, the natural and uncontrolled yarn charge effects are registered through its movement. The charge effects are received by fixed electrodes, positioned in relation to the moving yarn, as a receiver array in the yarn movement path with a variable sensitivity to determine a changing total charge in at least one section of the electrode array.  A time-related and periodically changing total charge is produced, where the yarn (1) passes by a single receiver (25) with a periodic changing sensitivity related to the location in the yarn movement direction. The changing total charge at the electrode array is established as a main component of a concentrated narrow-band frequency mix. The generally periodic changing total charge is converted by a charge amplifier into generally periodic voltage swings as a usable signal. The signal is processed to show the frequency of the main component of the signal or a value from a mathematical expression especially for the yarn speed or running length. A breach of a threshold value gives detection or display of the yarn movement.  The receiver has a grid array of electrodes with grid rods (2) in a periodic series repetition in the yarn movement direction, and in a fixed geometric array in rows to the yarn (1) moving past. They are arranged in similar groups (21,22) under each other. The grid rods (2) are at the same interval, or different intervals from the yarn (1). The rod groups (21,22) are positioned on different planes, or they are all on the same plane. All the grid rods (2) in one plane are linked together, and the rods of one group (21) alternate with the rods of the other group (22) along the yarn movement path. The grid rods (2) can be curved to cover the yarn (1) wholly or partially on a cylinder mantle surface instead of the straight planes. An Independent claim is included for an assembly where the grid rods (2) of one group (21) are linked conventionally to an earth mass potential (5) and the other group (22) is connected to the input of an amplifier (6) as a charge amplifier. Preferred Features: The grid rods (2) of one group (21) can be connected to the positive input of a difference amplifier acting as a charge amplifier, and the rods of the other group (22) are linked to the negative input of the amplifier. The amplifier has a charge difference amplification circuit for only one operation amplifier, with a condenser in an inverted feedback path. It also has a resistance with its first connection linked to the inverted input of the operation amplifier and the other connection is the negative input of the charge difference amplification circuit. Selectively, a second resistance has a first connection with the non-inverted input of the same operation amplifier and the other connection at the positive input of the charge difference amplification circuit. If there is no second resistance, the non-inverted input of the operation amplifier also acts as the positive input for the charge difference amplification circuit. The processing of the useful signal uses a phase locked loop (PLL) to give an alternating voltage oscillating in the required shape with the frequency of its main component and especially as a sine wave oscillation or a series of rectangular pulses. Or it gives a direct voltage, proportional to this frequency, connected to the amplifier of the difference amplifier. An additional or alternative signal processing is within the signal flow between the receiver and the output or the PLL, with at least one frequency filter, control amplifier, threshold value switch and a precision comparator. The display shows the frequency of the main component of the useful signal, or the yarn speed, or the running length of the yarn. It has a pulse counter for the exponent of the periods of the main component, respectively from the pulses as a series of rectangular pulse series from the threshold value switch, or the PLL. A threshold value switch or an additional PLL detects a breach of the threshold value of the useful signal amplitude.