Experimental Analysis on the Effectiveness of Kinematic Error Compensation Methods for Serial Industrial Robots

Error analysis and compensation method of displacement measurements based on reflection projection imaging

The instantaneous angular speed (IAS) signal is currently being increasingly applied in the fault detection of rotating machinery, in the actual operating conditions of industrial robot joints, encoders experience complex variable rotation speeds. This presents significant challenges for fault detection in industrial robots based on the IAS signal collected by the encoder. This paper proposes an improved error compensation method specifically designed for non-stationary conditions. A coefficient of variation-guided local polynomial fitting method (VLPF) is introduced to mitigate engraving and subdivision errors in incremental grating encoders operating at varying rotation speeds. First, an error compensation model is developed by analyzing these errors. Next, the relationship between the coefficient of variation (Cv), based on power spectral density (PSD), and the optimal fitting window length at different speeds is established through simulation analysis. The IAS signal of the encoder is then collected from an industrial robot RV test bench and corrected using the proposed method. Finally, simulation and experimental results show that the VLPF method effectively suppresses IAS signal errors during rapid changes in rotation speed. The proposed error compensation method under operating conditions reduces encoder errors by approximately 63.37%, which will be more advantageous to use IAS signal for fault detection.

An error compensation method for on-machine measuring blade with industrial robot

Accuracy enhancement of five-axis CNC machines through real-time error compensation

High-resolution integral imaging display with precise light control unit and error compensation

In order to increase the machining accuracy of industrial robots, a drilling system based on a 3D passive scale tracker (3DPST) and Epson industrial robot was established. The real-time positioning errors of the robot were measured by 3DPST, and the orientation errors were analyzed according to position coordinates on a circular path. Therefore, the 6-DOF pose errors of the robot were measured. Building upon this foundation, a cyclic compensation method for robot pose errors was proposed. This method prioritizes the compensation of orientation errors followed by the compensation of positioning errors. Robot circular path tests and drilling experiments of aluminum alloy and plexiglass materials are carried out to verify the effectiveness of the error measurement compensation method. The results of coordinate measuring machine measurements indicate that, after robot error compensation, the machining accuracy of the machined holes in both materials is significantly improved. The positioning errors of the machined holes for aluminum alloy decreases from the range of 1.188–1.576 mm to 0.154–0.215 mm, while for plexiglass, it decreases from 1.226–1.437 mm to 0.132–0.183 mm.

The spindle error and geometric error are the main sources of inaccuracy in CNC machining. With the rising of the machine tool parts' temperature, the spindle error and geometric error increase continually, and the error curves have a nonlinear distribution. To analyze the thermal effects on spindle error and geometric error, an experiment is carried out. To improve the machining accuracy of a CNC machine, an error model is proposed based on orthogonal polynomials. With the application of the orthogonal polynomials, the polynomial regression can be transformed into multiple linear regressions which are easier to calculate. In order to implement the real-time error compensation for the thermally induced spindle error and geometric error, an error compensation method is proposed based on the external coordinate offset. The thermally induced spindle and geometric error are compensated by 90 % compared with no compensation.

According to the robot positioning accuracy, this paper proposed an error compensation method after updating the controller parameters based on the D-H parameters model and Dynacal system. The proposed method is effectiveand was validated on the developed robot of which the mean error was reduced to 0.092mm. The method can greatly improve the positioning accuracy of the robot.

In a previous paper, the writers developed the equations for the main errors in the quadrant electrometer for the measurement of power factor, and checked their equations experimentally, the main sources of error being the unavoidable shunting capacity to ground of the test specimens and the charging current from the electrometer needle to the quadrants. In the present paper methods of experimental compensations and elimination of these sources of error are described. Methods of compensation for capacity to ground have been presented before, and in this paper merely some additional refinements are given. The method of compensation for errors due to the charging current in, the needle circuit is believed to be new; the method is described herein, the equation is derived in full, and an experimental check is given of the accuracy of the equation.

A novel spindle inclination error identification and compensation method in ultra-precision raster milling

In order to improve the precision of Coordinate Measuring Machine(CMM), error compensation method is researched, especially the basic steps of error compensation, which are errors sources analysis, errors modelling and errors measurement, the experiment is done which proves the feasibility.

The precision turning process has attracted enormous interest in the standardized and mass production of micro-shafts because it produces more efficiency and lower cost compared with the electrical-discharge machining method and micro-machining method. However, there are many critical factors that influence the dimensional accuracy of micro-shafts, such as the error of workpiece deformation, cutting force, and tool setting error. In this paper, a novel error compensation method was proposed to improve the dimensional accuracy of micro-shafts manufactured with the conventional precision machine tool, based on the constant force cutting method and tool path planning. Firstly, a cutting force model was established considering the effect of the tool nose radius, and the finite element method was used to simulate the turning process and predict the workpiece deformation. Secondly, an error analysis model was created by taking tool setting error, workpiece deformation error, and multi-process cumulative error into account, and the optimized tool path and cutting parameters were obtained. Finally, a series of turning experiments were carried out to verify the error compensation strategy and the cutting force model. The results show that the dimensional error of the micro-shafts with a large length-diameter ratio (l = 5 mm, d = 0.4 mm) can be reduced by 90% by means of the proposed error compensation strategy. In addition, the maximum prediction error of cutting forces is less than 8.6%, and the effect of cutting parameters on cutting forces can be concluded as “feed rate > depth of cut > spindle speed.”

Flatness and surface quality are important quality indexes of strip steel, and roll wear will directly affect the product's flatness and surface quality. Online roll profile measurement technology can obtain the information of roll profile in real time, guide the optimization of roll change rhythm, and improve the flatness control ability of rolling mill and surface quality of strip product. However, the error caused by roll displacement, clearance, roll thermal crown, and other factors is usually the same order of magnitude as the roll shape or roll wear, or even one order of magnitude higher. So error compensation is the key to ensuring the accuracy of online roll profile measurement. Herein, the position measurement technology of the roll bearing block is considered in the online roll profile measurement, and the measurement error caused by the deviation of the roll axis is separated. The thermal crown model is established to separate the measurement errors caused by the thermal crown. The error compensation model of online roll profile measurement is established, and the simulation calculation is carried out. This error compensation method is of great significance to improve the accuracy of online roll profile measurement and realize the fine management of mill roll in service.

This paper presents an error compensation method for fixed-width canonic signed digit (CSD) multipliers that receive a W-bit input and produce a W-bit product. To efficiently compensate for the quantization error, the truncated bits are divided into two groups (major group and minor group) depending upon their effects on the quantization error. The desired error compensation bias is first expressed in terms of the truncated bits in the major group. Then the effects of the other truncated bits in the minor group are taken care of by a probabilistic estimation. Also, an efficient sign extension reduction method applied to the fixed-width CSD multipliers is proposed. By simulations, it is shown that 25% reduction in the truncation error and 13% hardware complexity can be achieved by the proposed error compensation and sign extension reduction methods, respectively.

This paper studied the primary sources, evolution rules, and influence mechanisms of the damping anisotropy of the whole-angle hemispherical resonator gyroscope from the perspective of the fabrication process and analyzed the influence of temperature change on the damping anisotropy. An error identification and compensation method is proposed to suppress the effect of the damping anisotropy error on the gyroscope's bias error. According to the energy controller's output, this method involves applying the recursive least squares method to identify the damping anisotropy error and the damping axis angle in real time. Subsequently, a compensation signal is synthesized based on the identification results and applied to the angular rate control loop to compensate for the damping asymmetry error online. The experimental results show that the peak-to-peak value of the angular rate output harmonic error of the gyroscope is reduced from 0.023°/s to 0.005°/s after the error compensation, which is an improvement of about 5 times. In addition, the peak-to-peak value of the gyroscope angular dependent bias error decreases from 0.7072° to 0.08268°, which improves by 8.55 times, and the linearity of the angular measurements is also significantly improved. This methodology can be widely applied to gyroscopes operating in whole-angle mode, which is essential for fundamentally reducing the bias errors of the gyroscope induced by damping asymmetry.