Kaan Erkorkmaz

• PhD
• Professor at University of Waterloo

This paper presents a pole-placement technique to achieve active vibration damping, as well as high bandwidth disturbance rejection and positioning, in ball screw drives. The pole-placement approach is simple and effective, with an intuitive physical interpretation, which makes the tuning process straightforward in comparison to existing controller...

This paper presents the modeling and motion controller design for a linear motor driven T-type gantry and worktable. The worktable motion, which is referred to as the x-axis, is considered independently of the gantry and is controlled using a loop shaping filter. The gantry (or y-axis) is actuated by dual direct drive linear motors and is coupled t...

A feedrate optimization technique has been developed for minimizing the cycle time in machining spline toolpaths. Axis velocity, torque and jerk limits are considered throughout the motion in order to ensure smooth and linear operation of the servo drives with minimal tracking error. Feed modulation is achieved by manipulating segment durations whi...

This paper presents a trajectory planning strategy for maintaining the tool positioning accuracy in high speed cornering applications. A 3D contour error estimation algorithm is presented for determining the geometric deviation from arbitrarily shaped toolpaths. Two spline fitting strategies are developed for smoothening sharp corners. The under-co...

High-accuracy modeling of machine tool dynamics is essential for advanced process planning and monitoring. However, modeling high-speed multi-axis machines is challenging due to the inherent coupled and nonlinear multibody dynamics and structural flexibility. This complex modeling task is addressed by a new approach in which the control dynamics an...

In large-scale machine tool applications, the presence of low structural natural frequencies limits the cutting capabilities of the machine. The machine tool joints interact with the structural mode shapes, hence, the feed drive system characteristics can significantly influence the resultant dynamics at the cutting point. This paper investigates t...

Motivated by the fact that the tool cutting point (TCP) receptance demonstrates significant variation between the idle and in-motion conditions of a machine tool, this paper studies the relationship between guideway friction and TCP dynamics. The fundamental effect is modelled and demonstrated on a laboratory testbench considering structural mechan...

This paper presents a new control structure for ball screw drives (BSDs), which achieves position tracking through an outer loop, and active vibration damping for dynamic stiffness enhancement through an inner loop based on H2-synthesis. As an advancement over earlier BSD control methods with active damping, the proposed technique is able to consid...

In large machine tool applications, where machine's productivity is limited by structural chatter vibrations, an accurate dynamic characterization is vital for predicting reliable stability lobes. Motivated by the fact that the sweep milling force excitation method shows a great potential, this paper conducts a numerical stability analysis for opti...

This article describes a new frequency-domain multi-input multioutput linear time-invariant (LTI) system identification algorithm for accurate model construction suitable for motion control systems. The proposed method can capture the effects of time-delay, lightly damped poles (structural resonances), as well as highly damped complex or real poles...

Additive manufacturing (AM) enables freedom of design, part complexity, and customization with minimal added cost, by fusing materials layer upon layer. AM, in general, is considered to have great potential in complementing conventional manufacturing methods. Functional parts with high strength to weight ratio generated using structural topology op...

This paper presents a tri-dexel geometric engine integrated simulation model for the gear hobbing operation. The process kinematics are modeled and validated using CNC signals from a Liebherr LC500 hobbing machine. Workpiece geometry updating and cutter-workpiece engagement (CWE) calculations are efficiently realized in the tri-dexel engine. 3D for...

Harmonic positioning errors can negatively affect the positioning accuracy of the ball screw drive system. This paper addresses the problem of harmonic positioning error suppression in ball-screw drives using Adaptive Feedforward Cancellation (AFC). AFC method is integrated with the dual (i.e., rotational and translational) feedback structure used...

Virtual process planning offers advantages in terms of predicting servo and contouring errors ahead of time, and taking corrective action by modifying the program or CNC parameters. Successful application of virtual process planning requires accurate models that capture the dynamics of feed drives. Identification of such models is typically time co...

In large machine tools, where structural dynamics significantly influences the cutting stability, judicious selection of the servo control parameters can increase the damping, thereby improving the chatter stability. This paper presents a new strategy for feed drive controller tuning, which takes this effect into consideration. The proposed strateg...

Direct drive rotary and linear actuators significantly enhance the performance of multi-axis machine tools. The absence of mechanical gearing, however, increases the nonlinear dynamic coupling between the axes, making it challenging to identify accurate virtual models or so-called ‘digital twins’. This article presents a new approach to estimate no...

In large heavy-duty machine tool applications, the parametrization of the controller that is used for the positioning of the machine can affect the machine tool dynamics. The aim of this paper is to build a Multiple-Input and Multiple-Output model that couples the servo controller and machine tool dynamics to predict the frequency response function...

This paper describes a new virtual model for predicting the uncut chip geometry and cutting forces in power skiving, which is a high-speed, versatile gear cutting process. The developevd kinematic model is applied in a dexel-based solid modeling engine to extract three-dimensional uncut chip geometry, from which the two-dimensional cross section is...

The productivity of the machining operations realised on lightly damped steel welded workpieces is drastically limited by chatter vibrations. This paper introduces a portable system to actively damp out workpiece vibrations. An electromagnetic actuator magnetically clamped onto the workpiece is used both to measure the structural response and to pe...

Gear shaping is, currently, the most prominent method for machining internal gears, which are a major component in planetary gearboxes. However, there are few reported studies on the mechanics of the process. This paper presents a comprehensive model of gear shaping that includes the kinematics, cutter-workpiece engagement (CWE), and cutting forces...

Elastic deflection of cutting tools relative to the workpiece is one of the major factors contributing to dimensional part inaccuracies in machining. This paper examines the effect of tool deflection in gear shaping and its effect on the gear's profile form error, which can cause transmission error and noise during gear operation. To simulate elast...

In this paper, mechatronic design, actuator optimization and controls of a long-stroke (20 mm) linear nano-positioner are presented. The mechatronic design is described in terms of the stage's most prominent features regarding mechanical design, assembly, actuator configuration, and power supply. A novel air-bearing/bushing arrangement has been use...

In this study, a precision motion stage, whose design utilizes a single shaft supported from the bottom by an air bearing and voice coil actuators in complementary double configuration, is evaluated for its dynamic properties, motion accuracy, and potential machining force response, through modal testing, laser interferometric metrology, and spectr...

Chatter vibrations are a major limitation for rough milling operations, leading to productivity reduction, low tool life and poor surface finish. It has been shown recently that the machine tool's own drives can be used to increase the stability limit related to structural modes of the machine. To damp the low frequency modes, a new feedback loop i...

Chatter vibrations are a major limitation for ma chining operations and lead to productivity reduction, low tool life and poor surface finish. Active damping with the machine tool's own drives can be used to increase the stability limit related to structural modes of the machine. Various feedback strategies can be used measuring the vibrations with...

Optimality and computational efficiency are competing objectives in the design of feedrate optimization algorithms for spline toolpaths. This paper presents a new approach, in which the use of Linear Programming (based on the ‘pseudo-jerk’ concept) is combined with a novel windowing algorithm to handle long toolpaths. The windowing uses the Princip...

Shaping is a versatile process for machining gear teeth on complex monolithic components, which cannot otherwise be produced using other methods (like hobbing) due to geometric constraints. This paper presents a new model to accurately predict the chip geometry and cutting forces in shaping. Kinematics of gear shaping is modeled and verified. Cutte...

In spline toolpath interpolation, a crucial point is solving the mapping between the spline parameter (u) and actual arc length (s) accurately, so that the toolpath is traveled without undesirable fluctuations or discontinuities in the feedrate profile. To achieve this, various techniques have been proposed in literature, including Taylor series in...

Chatter vibrations coming from the machine tool structure are a major limitation for heavy duty milling operations. Passive and active dampers can be added to increase the productivity. However, the price and required space of these absorbers are important drawbacks for their use in the industry. In this work, the machine tool's own drives are used...

On-the-fly laser drilling requires the use of acceleration continuous trajectories, which are typically planned using time parameterized spline functions. In this operation, the choice of hole drilling sequence, and positioning timings in between the holes, play a critical role in determining the achievable cycle time. This paper presents a new alg...

There has been increasing attention to the use of voice coil actuators (VCAs) for precision motion applications. In this paper, a detailed design of a cylindrical VCA is presented. Different options for the overall configuration are evaluated according to various criteria and design variables are defined for the chosen configuration. After that, op...

This paper presents a new and comprehensive strategy for planning minimum cycle time tool trajectories subject to both machining process related constraints, and also limitations of the feed drive control system. The machining process is considered by computing the workpiece-tool engagement along the toolpath and setting local feed limits to mainta...

This paper presents a new method for designing control laws for ball screw drives by directly optimizing the load side disturbance response against cutting forces. The design applies, concurrently, the principles of pole placement and loop shaping, and is easy to implement in practice. In addition to good low frequency disturbance rejection, the co...

Calcium PolyPhosphate (CPP) is a biodegradable inorganic polymer that when formed as a porous structure with interconnected pores of a desired size range holds great potential for certain tissue engineering applications. While possessing desirable characteristics of biocompatibility with acceptable compressive strength, the brittle nature of porous...

In many machining processes cutting forces are of harmonic nature. The frequency content of these forces may extend far beyond the closed-loop bandwidth of the commonly used feed drive controllers. In ball screw drives, high–frequency disturbances may also originate from repetitive errors synchronized with the rotation of the ball screw. To improve...

Any meaningful initiative to improve the teaching and learning in introductory control systems courses needs a clear test of student conceptual understanding to determine the effectiveness of proposed methods and activities. The authors propose a control systems concept inventory. Development of the inventory was collaborative and iterative. The di...

This paper presents a new and time-optimal trajectory generation technique for 5-axis on-the-fly laser drilling. Trajectories for individual hole clusters are optimized by minimizing the integral square of the 4th time derivative, and by adjusting the velocity and acceleration conditions at the hole locations to enable the maximum time compression...

This paper presents a new X–Y stage concept for precision machine tools. A large work area (300 mm × 300 mm) is achieved using a T-type gantry arrangement, which locates the work table supported on a vacuum preloaded air bearing on top of a reference granite surface. Actuation is provided with direct drives that fulfil the functions of motion contr...

This paper presents a genetic algorithm (GA) for identifying virtual models of machine tool drives with minimal intervention to the production machine. The proposed solution builds on the “rapid identification” concept reported earlier in literature, in which a short series of motion data is captured from the Computer Numerical Control (CNC) and us...

Elastic deformations occur in ball screw drives typically due to inertial forces, guideway friction, and cutting forces. This results in elongation and compression of the ball screw, which deteriorates the dynamic linear positioning accuracy. Closing the control loop with a linear encoder helps to alleviate this problem to a certain extent. However...

With the growing demands to machine complex dies, moulds, aerospace, automotive, and biomedical parts in shorter cycle time, the utilization of Non-Uniform Rational B-Spline (NURBS) toolpaths has become more important than ever before. There are two challenges associated with realizing a successful NURBS trajectory generator—minimizing feedrate flu...

INTRODUCTION In order to meet industry demands for improved productivity and part quality, machine tools must be equipped with faster and more accurate feed drives. Over the past two decades, research has focused on the development of new control strategies and smooth trajectory generation techniques. These developments, along with advances in actu...

This paper presents a new and computationally efficient feedrate optimization strategy for spline toolpaths. The technique combines analytically derived compatibility equations with a heuristic search method, which helps generate feed profiles with reduced cycle time while adhering to axis velocity, acceleration, torque, and jerk constraints. Feed...

This paper presents a precision control strategy for ball screw drives. Axial vibrations are modeled and actively compensated in the control law, which enables the realization of high positioning bandwidth. Lead errors, arising from imperfections of the screw, are modeled and removed from the loop by offsetting their effect from the command traject...

This paper presents a motion control strategy that utilizes a combination of vibration avoidance, sliding mode control, and torque ripple and friction compensation techniques to facilitate high bandwidth–high accuracy tracking in ball screw drives. Torsional vibrations are modeled with finite element analysis and experimentally identified. Excitati...

This paper presents a technique for rapid identification of machine tool drives by conducting a short G-code test. The proposed strategy uses commanded and measured axis profiles and requires minimal intervention to the servo control loop. The drive system is identified as a whole, including the feed mechanism, motor, amplifier, and the control law...

This paper presents a technique for extracting virtual models of machine tool drives with minimal intervention to the production machine. The identification is carried out by running a short G-code test and capturing commanded and measured position readings. The methodology is fairly general and can be applied to different types of drives (linear o...

This paper presents a tracking control strategy for high speed ball screw drives. Rigid body motion is controlled using adaptive sliding mode control. Torsional vibrations are modeled, experimentally identified, and compensated in the control law using notch filtering and active cancellation techniques. Attenuation of torsional resonances improves...

This paper presents a comprehensive virtual simulation model for CNC systems. The Virtual CNC (VCNC) has a modular architecture, allowing a real CNC to be prototyped quickly from standard library functions for feed drive models, feedback devices, axis control laws, and trajectory interpolation. Additional CNC modules can easily be prototyped and in...

The paper presents a comprehensive virtual simulation model of a realistic and modular CNC system. The Virtual CNC architecture represents an actual CNC, but with modular feed drives, sensors, motors, and amplifiers. The CNC software library includes a variety of trajectory interpolation and axis control laws. Constant, trapezoidal and cubic accele...

Real-time controllers have traditionally used computer hardware systems that require expertise in hardware knowledge before the controller can be effectively implemented. This paper introduces a single-processor PC-based real-time motion controller developed using QNX 6.0 Neutrino operating system. Using the advantages of a distributed software sys...

This paper presents a parameterization and an interpolation method for quintic splines, which result in a smooth and consistent feedrate profile. The discrepancy between the spline parameter and the actual arc length leads to undesirable feed fluctuations and discontinuity, which elicit themselves as high frequency acceleration and jerk harmonics,...

This paper investigates the effectiveness of adaptive sliding mode control (SMC) for precision tracking in high speed machine tool drives. Dynamics of the feed drive, comprising of rigid body motion, guideway friction and ball screw vibrations, are identified. Two strategies are developed. The first one considers rigid body dynamics in the plant an...

A servo control system capable of delivering rapid and accurate feed motion is a necessity for high speed machine tools. The control law must be designed to provide a high tracking bandwidth as well as adequate disturbance rejection and parameter variation robustness, in order minimize the following errors in each axis. This also contributes to the...

Accurate modeling and identification of the feed drives' dynamics is an important step in designing a high performance CNC. This paper presents a method for identifying the dynamic parameters, as well as the friction characteristics of machine tool drives. The inertia and viscous friction are estimated through an unbiased least squares scheme. The...

Reference trajectory generation plays a key role in the computer control of machine tools. Generated trajectories must not only describe the desired tool path accurately, but must also have smooth kinematic profiles in order to maintain high tracking accuracy, and avoid exciting the natural modes of the mechanical structure or servo control system....

An adaptive sliding mode control technique is presented for the control of high speed feed drives. The proposed control system is robust against uncertainties in the drive's parameters, maximizes the bandwidth within physical limitations, and compensates for external disturbances such as friction and cutting force. The algorithm is briefly presente...

Lead errors and elastic deformations can result in significant positioning error in ball screw drives. Although it is possible to remove their effect by closing the control loop with a linear encoder, this brings about a bandwidth limitation due to the inclusion of drive flexibility into the servo loop. In this work, a compensation strategy is pres...

Thesis (Ph.D.)--University of British Columbia, 2004. Includes bibliographical references.