CNC turning machine

A turning machine is characterized by a new and improved control and mechanism for positioning the turning tool on the head. A CNC control issues command signals for selectively positioning the tool on the head. These signals are developed from an encoder which provides the instantaneous position of the rotating part being turned and from a program in the CNC containing information about the part. A closed loop control system receives these command signals and converts same into a control current for a linear motor which is the prime mover controlling the positioning of the tool on the head. The linear motor operates a carriage on the head and the cutting tool mounts on the carriage opposite the connection of the linear motor to the carriage. The carriage is a hollow bar guided on the head by sets of rollers which are cooperatively arranged to provide yieldably forceful constraint of the bar. The rolling action of the bar on the head provides a low friction, low inertia construction enabling rapid response to CNC commands. The head also contains various sensors providing position and velocity feedback information for use by the closed loop control. The closed loop control contains various circuit components organized and arranged to provide fast and faithful response to command signals. The machine has the ability to accurately turn complex parts where position information is being rapidly updated, often in the tens of kilohertz frequency range. Different parts can be turned by merely changing the CNC program.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates generally to turning machines and specifically to a 
new and unique CNC turning machine which is adapted for complex turning of 
parts such as pistons. 
An example of a known turning machine is illustrated in U.S. Pat. No. 
3,869,947, commonly assigned. In the turning machine disclosed in thar 
patent, a part to be turned, for example a piston, is suitably chucked and 
rotated about its axis at an appropriate speed. A cutting tool is arranged 
to make a pass along the rotating part and machine the outer part surface, 
i.e. the piston skirt. As the cutting tool is making its axial pass along 
the part, the cutting tool's radial position is continuously correlated 
with the rotation of the part to produce a desired shape. This correlation 
is achieved by a cam and follower system. Such a system is capable of 
imparting both eccentricity and taper to the part, i.e. complex turning. 
In other words in the case of a piston, the system is capable of producing 
either straight or tapered skirts of either circular or elliptical cross 
section, depending upon the desired shape. 
Such a turning machine is well suited for making large numbers of identical 
parts. However if different shaped parts are to be turned, the machine 
must be shut down for change-over. When such shut-down occurs, the machine 
is removed from productive use, and where precision parts are involved, as 
is usually the case, care must be taken to ensure that the new cam and the 
follower produce the desired precision. The amount of set-up time for the 
new cam also adds to the total machine downtime. 
Turning operations of the type conducted on piston skirts typically involve 
relatively high rotational speeds for the pistons. In the cam and follower 
type system described above, the dynamics of the machine and mechanism can 
limit the ability of the follower to track the cam. Hence minor changes in 
the cam surface shape may be difficult to follow, and there is necessarily 
a limit to the ultimate precision with which parts can be machined by such 
an apparatus for a given production rate. 
Another prior art approach to controlling the radial position of the tool 
head in a piston turning operation is disclosed in U.S. Pat. No. 
4,203,062, issued May 13, 1980 to Bathen for "Machine Tool Control 
Systems." The Bathen system employs computer numerical control with a 
feedback loop which compares a position signal representing the present 
position of the tool to a programmed position signal to produce an error 
signal which controls energization of a linear motor driving the tool. 
The present invention is directed to a new and improved turning machine 
which possesses a number of important advantages over prior machines. 
One important advantage is that the present invention eliminates the 
mechanical cam and follower type system by using numerical input data to 
define the part shape. This data is acted upon by a CNC system which 
generates appropriate commands to control the cutting tool position at all 
times during turning. Hence a turning machine embodying principles of the 
invention is not limited by the mechanical dynamics of the prior cam and 
follower systems which established an ultimate limit to the machine's 
capabilities. 
Because the control data is embodied in electronic form in the practice of 
the present invention rather than as a mechanical model like a cam, there 
is no elaborate mechanical change-over required when part shape is to be 
changed. Rather the CNC is provided with a new part program for the new 
part, and it automatically acts upon the new part program data to issue 
appropriate commands for control of the cutting tool. 
Moreover, with the elimination of the mechanical cam and follower, the 
present invention affords the opportunity for attaining even higher 
degrees of precision in the high speed turning of parts. 
Not only is the versatility of a turning machine significantly enhanced 
since it can handle many different part sizes, but with improved 
efficiency and precision potentials, the opportunity for significant 
productivity gains is also presented by the present invention. 
The general idea of applying a CNC system to a cutting tool is of course 
known. For example CNC lathes are representative commercial products. 
However in the context of a high speed turning apparatus such as a piston 
turning machine, the application of CNC technology has heretofore been 
deemed impractical because of inherent mechanical limitations in mechanism 
for positioning the cutting tool. 
Consider a situation where a part is to be turned at say several thousand 
RPM and is to be provided with an elliptical cross sectional shape. The 
cutting tool must make two reciprocations radially of the part for each 
complete revolution of the part. In the case of a piston rotating at 2400 
RPM, this means that the cutting tool is required to execute precisely 
controlled linear oscillations at a frequency of 80 hertz. For example if 
it is assumed that the acceleration of the tool is required to follow a 
0.007 inch radial displacement at this speed, the acceleration amounts to 
37 feet per second per second. In order to achieve this magnitude of 
response, the mass associated with the oscillating cutting tool must be 
small. Yet at the same time that the mass, including the cutting tool, is 
executing this oscillatory motion, they are being subjected to a load 
imposed by the interaction of the cutting tool with the rotating part. The 
requirements of minimizing the mass associated with the cutting tool in 
order to attain a satisfactory response at the expected oscillatory 
frequencies and of accurately linearly guiding same with minimum static 
and dynamic friction, are seemingly inconsistent with requirements that 
the cutting tool and its associated mass be sturdily constructed and 
supported to react the loads imposed on them without undesired effects 
such as tool chatter and/or deflection so that the desired contour of the 
part can be achieved. Moreover, since many parts are of complex contour 
including an axial taper, such taper usually has to be taken into account 
as well. 
Accordingly, another aspect of the present invention involves a new and 
unique construction for the mechanical mechanism which oscillates the 
cutting tool. Among the new and unique features are the prime mover which 
is utilized to impart oscillatory motion to the cutting tool, the 
construction of the cutting tool carriage, and the arrangement for guiding 
the carriage on a head. 
In the preferred embodiment of the invention the prime mover comprises a 
linear motor, sometimes referred to as a voice coil motor. This prime 
mover has a low inertia armature for fast response, yet it is capable of 
precise movement while exerting ample force to counter cutting loads 
imposed when the cutting tool interacts with a part being turned. The 
cutting tool carriage is operated by the motor armature. A sturdy, yet low 
friction, mounting of the carriage on the head also assists in reacting 
the cutting loads while enabling the desired oscillatory action to be 
obtained so that accurate parts are consistently produced. 
Another aspect of the invention involves the cooperative relationship 
between the CNC system and certain mechanical mechanisms of the machine. A 
portion of the CNC operation is devoted to a closed loop control with the 
part being turned whereby the relative axial position of the part to the 
cutting tool and the rotational position of the part about the axis of its 
rotation are precisely controlled and known at all times. The CNC acts 
upon the part program in conjunction with the aforementioned closed loop 
control to issue correlated commands for use in controlling the voice coil 
motor, and hence the radial oscillation of the cutting tool. These 
commands are transmitted by via a high speed data link to a position 
profile computer which translates the commands into an appropriate form 
for causing the voice coil motor to produce the double oscillation of the 
cutting tool per each revolution of the part when an elliptical contour is 
being machined. 
The position profile computer is a system dedicated to the radial 
positioning of the cutting tool, and it forms a portion of a closed loop 
control for the cutting tool position. Associated with the voice coil 
motor and carriage, are various sensors which provide feedback signals to 
this latter closed loop control. These are all operatively related such 
that digital data from the CNC and feedback signals from the various 
sensors are appropriately processed to produce a control current for the 
voice coil motor which produces the desired oscillation of the cutting 
tool. 
Accordingly the dedicated system comprises digital circuit components 
performing digital calculations. It also has digital-to-analog devices 
organized and arranged to act upon certain digital commands to produce an 
appropriate analog control current for the voice coil motor. As will be 
seen leter, there are particular relationships involved in this closed 
loop control which are advantageous in causing the tool to faithfully 
follow the CNC digital commands. 
The foregoing features, advantages, and benefits of the invention, along 
with additional ones, will be seen in the ensuing description and claims 
which should be considered in conjunction with the accompanying drawings. 
The drawings disclose an exemplary, presently preferred embodiment of the 
invention according to the best mode contemplated at the present time in 
carrying out the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The reader's comprehension of principles of the present invention which 
will be explained can perhaps be expedited by considering first a 
description of certain relationships which are disclosed with reference to 
FIGS. 1 through 5. 
FIGS. 1 and 2 are diagrammatic views which illustrate a complex surface 20 
which is typical of a piston skirt. It is to be appreciated that FIGS. 1 
and 2 are diagrammatic in nature and therefore exaggerated in proportion 
to what would typically be the proportions in an actual piston. 
Surface 20 may be considered to comprise a longitudinal axis 22. While it 
also may be considered as having a generally frusto-conically tapered 
shape, the actual cross section through the surface is elliptical, as can 
be seen from consideration of FIG. 1 which is representative of both an 
end view and a typical cross section. 
Surface 20 may be mathematically defined in any of a number of possible 
ways. Because the disclosed preferred embodiment of the present invention 
utilizes a CNC, surface 20 is defined as a set of discrete points in 
space. These points are most conveniently identified in terms of a three 
dimensional coordinate system wherein one coordinate represents the 
angular location about axis 22 as referenced from a radial datum another 
coordinate represents longitudinal (i.e. axial) location along the length 
of axis 22 as referenced from a longitudinal datum, and the third 
represents the length of a radial to axis 22. For convenience, the angular 
coordinate is identified by the general symbol .theta., the longitudinal 
coordinate by the general symbol z, and the radial by the general symbol 
r. 
The degree of precision in the discrete point definition obviously involves 
the number of points used. In other words the finer the resolution, the 
more precise the surface definition. 
For convenience let it be assumed that there are a total of n increments 
around axis 22 so that each angular increment corresponds to 360/n 
degrees. In the longitudinal direction, the increments are typically quite 
small, generally thousandths of an inch or less. 
On this basis it can be appreciated that at each z coordinate, surface 20 
is defined by a sub-set of n data points each corresponding to a radial at 
each of 360/n increments about axis 22. Stated another way, the part 
surface definition at each z coordinate may be considered as a one 
dimensional matrix of 360/n radials. If there are m longitudinal 
increments, the entire surface is defined by a two-dimensional n.times.m 
matrix of the radials. 
In the disclosed embodiment n=360 so that there are 360 one degree 
increments about axis 22. In other words n runs from zero to 359 for each 
of m axial increments along the length of axis 22. The number of m 
increments depends upon the relation of the turning speed of the part and 
the axial feed rate of the tool as it makes its pass axially along the 
part and also to the part length. FIG. 3 illustrates this mathematical 
n.times.m matrix definition of surface 20. 
In the case of a complex piston, the turning machine of the present 
invention operates on a rough piston to cut the skirt to the size and 
shape of surface 20. The turning machine utilizes a mathematical surface 
definition such as that represented by the matrix of FIG. 3 to generate 
the appropriate motion of the cutting tool relative to the piston. The 
means by which this is accomplished will be explained in the later 
description. For now, a further diagrammatical description of how the part 
surface definition matrix is used in establishing the cutting tool motion 
is given with reference to FIGS. 4 and 5. 
As the piston turns about axis 22, its angular position about axis 22 is 
continuously monitored. Because the angular position of the cutting tool 
relative to axis 22 is known, and is essentially constant if the cutting 
tool tip oscillates substantially coincidentally with a radial to axis 22, 
the monitored angular position can be used to determine the angular 
coordinate of the part which is being presented to the cutting tool tip at 
any given instant of time as the piston rotates. 
Similarly if the longitudinal position of the part relative to the cutting 
tool is continuously monitored, the axial location of the cutting tool tip 
relative to the piston is also known at any given instant of time. 
Therefore at any given instant of time, these two conditions define the 
point on the piston which is being presented to the cutting tool tip. The 
turning machine of the present invention operates to act upon these two 
conditions, and the particular part program being executed by the CNC, to 
continuously position the cutting tool to the appropriate radial location 
so that the desired surface is cut in the piston skirt. 
This relationship is portrayed mathematically with reference to FIG. 4. The 
tool radial position is called the tool position profile and it is shown 
to be a function of the part surface definition matrix, and axial and 
angular positions of the tool relative to the part. The axial and angular 
positions are, of course, inherently also related to the respective axial 
and angular velocities. 
For convenience let it be assumed that the z-axis velocity, or feedrate, of 
the tool relative to the workpiece is constant and let it be further 
assumed that the surface which is to be cut in the part is a complex one 
like that described with reference to FIGS. 1 and 2. In order to cut an 
elliptical contour, it will be perceived that for each 180 degrees of 
rotation of the part, the cutting tool must make one complete radial 
reciprocation relative to the axis 22, i.e. one full oscillation. In other 
words for each revolution of the part, it is necessary for the tool to 
reciprocate radially inwardly and outwardly twice because of the nature of 
the elliptical contour. 
For further convenience in description let it be assumed that the general 
variable x represents the radial tool position relative to axis 22. For 
the illustrated example where there are 360 data points once around the 
circumference of the part, the control operates to generate a 
corresponding sequence of 360 data points for the tool position. In other 
words for the mth subset of the part position matrix, the control 
generates a corresponding set of data points for the variable x, i.e. it 
generates the tool position profile. 
FIG. 5 illustrates the relation of these x data points to the oscillating 
radial motion of the cutting tool. If it is assumed that the part is 
circumferentially located such that one end of the major axis of the 
elliptical cross section is presented to the cutting tool tip, the cutting 
tool must advance radially inwardly over the ensuing 90.degree. of part 
rotation since the minor axis of the ellipse is 90 degrees from the major 
axis. Because 90 degrees of part rotation provides 90 data points, there 
is a corresponding set of 90 data points generated for the variable x and 
these are depicted in FIG. 5 as occurring along the imaginary straight 
line segment 24. When an end of the minor axis of the ellipse is presented 
to the cutting tool tip, the cutting tool must then reverse direction so 
as to move radially outwardly during the next 90 degrees of part rotation. 
A second set of 90 data points defining the part surface between 90 and 
179 degrees of part rotation causes a corresponding set of 90 data points 
to be generated for the variable x. These 90 data points are indicated 
along the imaginary line 26 in FIG. 5. Based upon the description just 
given, the reader will appreciate that the cutting tool has executed one 
full oscillation during 180 degrees of part rotation. The second 
oscillation is portrayed by the segment 28 with its x data points being 
generated by the part rotation between 180 degrees and 269 degrees and by 
the segment 30 with its x data points generated by quadrant of part 
rotation from 270 degrees to 359 degrees. 
FIG. 5 is in an exaggerated form for illustrative purposes, and it shows 
that axial taper is being imparted to the part because each oscillation of 
the tool moves progressively increasingly radially inwardly. This taper is 
represented by drawing an imaginary line 32 through the radially innermost 
points of tool tip travel during each oscillation and a corresponding line 
34 through the radially outermost points. If there were no taper to the 
part the lines 32, 34 would be parallel to axis 22. 
The process continues in this manner until the entire part surface 
definition matrix has been processed by the control to produce a 
corresponding pattern of motion to the cutting tool resulting in the 
creation of the desired shape of the part being turned. 
The x data points which are generated by the control are acted upon to 
produce the corresponding motion of the cutting tool. Although the data is 
presented in digital form, the physical characteristics of the machine 
including both its mechanical and electronic components, coact such that a 
smooth machining action results. This is accomplished through the 
appropriate selection of the increments and/or through the characteristics 
of certain components of the system; for example in the electronics 
digital-to-analog conversion may be used. 
With this description of how the tool operation is mathematically related 
to the part surface definition, details of the machine itself can now be 
considered. 
FIGS. 6 and 7 illustrate in a general way the overall organization and 
arrangement of a presently preferred embodiment of turning machine 40 
according to the invention. The machine is illustrated for use in turning 
the skirt of a piston 42 which is suitably co-axially chucked and rotated 
about an axis 44 by means of a drive 46 and a live center spindle 48. This 
arrangement for chucking and rotating a part is conventional. 
The rotation for drive 46 is delivered by a servo motor 50. A tachometer 52 
and an encoder 54 are operatively coupled with the servo motor to develop 
electrical signals which are utilized by machine 40. Tachometer 52 
provides a signal representative of the instantaneous velocity of 
rotation, i.e. the turning speed, while encoder 54 provides a signal 
indicative of the instantaneous rotational position. The encoder and 
tachometer are conventional devices, and although it is known that the 
position and speed of a rotating shaft are mathematically related, it is 
deemed preferable to utilize two separate sensors to provide the 
respective speed and position information, rather than a single sensor. 
By way of example, encoder 54 may be a digital device which provides a 
digital signal indicative of the instantaneous rotational position in any 
convenient unit of measurement. For convenience the digital signal may be 
provided in terms of one degree increments of rotation about axis 44 and 
in this way is representative of instantaneous rotational position of 
piston 42 as it rotates about axis 44 relative to a circumferential point 
of reference. It will be appreciated that the signal repeats every 
complete revolution, but that during a revolution, each one degree 
increment is uniquely identified. By the proper circumferential mounting 
of piston 42 on the live center spindle and part drive, the point on the 
circumference of the piston skirt which is being presented to the tip of a 
cutting tool 56, is always correlated with the signal provided by encoder 
54 so that the encoder signal, at any instant of time, uniquely identifies 
the circumferential coordinate which is being presented to the cutting 
tool tip. 
The signal from encoder 54 is supplied to a CNC control 58. The manner in 
which the encoder signal is acted upon by CNC control 58 will be explained 
later. 
The signal from tachometer 52 is fed back to a servo amplifier 60 which 
controls the speed of servo motor 50. The servo amplifier 60 is of a 
conventional construction to perform a closed loop control of the servo 
motor with the tachometer 52 providing velocity feedback information 
utilized in the closed loop control. 
The command input to servo amplifier 60 is delivered by CNC control 58, and 
is to establish the appropriate turning speed. 
As will be appreciated from the early introductory description, tool 56 is 
caused to do an axial pass along the skirt of piston 42, and it is also 
concurrently caused to execute small radial oscillations relative to axis 
44 to impart eccentricity to the skirt. 
The axial component of motion of the tool relative to the part is provided 
by means of a slide 62 which is fed in a direction parallel to axis 44. 
For convenience this is identified as the z-axis. 
The z-axis feed is performed by means of a servo motor 64 which is 
operatively coupled with slide 62 by any suitable mechanical mechanism, 
for example a ball screw and nut. 
Servo motor 64 is a conventional device, and its shaft position and speed 
are monitored by an encoder 66 and a tachometer 68 in a similar manner to 
the monitoring of servo motor 50 by tachometer 52 and encoder 54. 
Tachometer 68 and encoder 66 provide feedback information to CNC control 
58. 
The CNC control forms a part of the closed loop control of servo motor 64 
by issuing appropriate signals to a servo amplifier 70 which in turn 
controls servo motor 64. The CNC control receives a program input which 
establishes the appropriate z-axis feed rate for the particular part 
involved, and the closed loop control operates to control the speed of 
servo motor 64 such that the appropriate z axis speed rate for slide 62, 
and hence like feedrate for cutting tool 56 axially along the piston 
skirt, are produced. 
The radial component of motion for the cutting tool, which for convenience 
will be referred to as x-axis motion, is imparted by a closed loop system 
which includes electronic and mechanical components. These will be 
described in considerably greater detail later on. With reference to FIGS. 
6 and 7 they are defined generally to include a linear motor 72 which is 
carried on slide 62. In this way the combined z and x axis motions are 
imparted to the cutting tool by means of the combined operation of servo 
motor 64 and linear motor 72. 
Linear motor 72 is a part of another closed loop control system which is 
used to achieve precise control of the x-axis motion of the cutting tool. 
Instantaneous position is monitored by a linear position transducer 74 and 
instantaneous velocity by a linear velocity transducer 76. These two 
transducers provide feedback signals to a servo amplifier and closed loop 
control 80 which controls linear motor 72. The input command to servo 
amplifier and closed loop control 80 is received from CNC control 58 via a 
high speed data link 82. An operating panel 78 is associated with CNC 
control 58 and is adapted to receive the part program which is to be 
executed. 
Briefly, CNC control 58 issues commands developed from a program defining 
the part surface to be generated, for example as described above with 
reference to FIGS. 1, 2 and 3, and servo amplifier and closed loop control 
80 acts upon the commands to provide corresponding control signals to the 
linear motor 72 to achieve the desired control of the tool x-axis 
position. For example, in the case of an elliptical contour, servo 
amplifier and closed loop control 80 serves to generate two oscillations 
of cutting tool 56 for each revolution of the piston 42. 
As can be seen in FIG. 7 the cutting tool tip may be slightly offset from 
the center line of the linear motor, but the x-axis motion is either 
exactly or at least substantially along a radial relative to axis 44. In 
this way, the position of the tip of the cutting tool is caused to 
describe the desired surface which is to be imparted to the piston skirt. 
FIGS. 8, 9, 10, and 11 illustrate in detail the mechanism by which x-axis 
motion is imparted to cutting tool 56. The mechanism comprises a head 82 
which is mounted by any suitable means on slide 62. Head 82 comprises a 
base plate 84, a rear plate 86, a top cap 88, and a top cover 90 assembled 
together and forming an enclosure for linear motor 72 and the two 
transducers 74, 76. 
As can be seen from consideration of FIGS. 8 and 10, base plate 84 
comprises a horizontal bottom wall 92 and upright side walls 94, 96. 
Hence, as viewed lengthwise of the x-axis in FIG. 10, base plate 84 can be 
considered to have a generally U-shaped cross section. 
At the forward end, i.e. the right hand end as viewed in FIG. 8, base plate 
84 is covered by top cap 88; the rear, or left hand, end is enclosed by 
top cover 90. Linear motor 72 is enclosed within the rear portion of the 
head and has an axis 97 along which it acts. 
Linear motor 72 comprises a magnet assembly 98 and a coil assembly 100. 
Magnet assembly 98 has an annular shape and an axis concentric with the 
axis 97. Coil assembly 100 also has an annular shape and is coaxial with 
magnet assembly 98. 
Magnet assembly 98 comprises a frame 102 of generally annular shape having 
a pair of bars 104, 106 (see FIG. 10) fixed to the outside to provide for 
its mounting on base plate 84. These bars rest on ledges 108, 110 of base 
plate 84, and frame 102 is securely attached to the base plate by screws 
112 passing through suitable holes in the base plate bottom wall and into 
tapped holes in the bars 104, 106. 
Magnet assembly 98 further comprises a magnet 114 disposed concentrically 
within frame 102. Magnet 114 has a circular annular shape and is of a 
length less than that of the frame. It is affixed within the frame in any 
suitable manner so as to be coaxial with axis 97. 
Magnet assembly 98 is enclosed at its rear axial end by means of an end 
plate 116 attached to frame 102. A central cylindrical hub 118 is mounted 
on and projects forwardly from end plate 116. In cooperation with magnet 
114, hub 118 defines a circular annular free space 120, and it is within 
this annular free space that a rear portion of coil assembly 100 is 
disposed. 
Coil assembly 100 comprises a circular tubular wall 124, or bobbin, which 
attached by means of a cap 126 at its forward end to a carriage 128. 
Carriage 128 in turn projects forwardly from cap 126 to terminate at a 
forward end containing a suitable tool mount 130 for tool 56. 
Carriage 128 is illustrated as a hollow tubular bar having an axis 
coincident with axis 97 and having a square transverse cross sectional 
shape as best seen in FIG. 10. The carriage axis is parallel to the 
x-axis, and the carriage is arranged for axial motion by linear motor 72. 
Carriage 128 is accurately guided on head 82 by sets of rollers. The 
rollers provide for low friction mounting, yet are sufficient to react 
cutting loads so that at all times during turning operations the cutting 
tool is enabled to accurately follow commands and cut a desired surface on 
the part being turned. 
The rollers for guiding carriage 128 are arranged in sets. For convenience 
these are referred to as a vertical acting set and a horizontal acting 
set. The carriage is vertically constrained by the vertical set of 
rollers, and it is horizontally constrained by the horizontal set of 
rollers. 
The vertical set is seen with reference to FIGS. 8 and 10 where it is shown 
to comprise a lower half-set 132 and an upper half-set 134. The upper 
half-set 134 is spring-loaded while the lower half-set 132 is not. 
The upper half-set comprises four individual circular rollers, or wheels, 
138 of identical size. Two of these rollers are on the ends of a rear axle 
140 while the other two are on the ends of a forward axle 142. The rear 
axle 140 is supported on a rear yoke 144 and the forward axle 142 on a 
forward yoke 146. The two yokes 144, 146 are joined together by a leaf 
spring assembly 148 which extends axially between a forward portion of 
rear yoke 144 and a rearward portion of forward yoke 146. The attachment 
of the leaf spring assembly to the yokes is by any suitable means, such as 
by screws passing through apertures in the leaf spring assembly and into 
tapped holes in the yokes. The leaf spring assembly is centrally disposed, 
as viewed in FIG. 10. 
The leaf spring assembly is further provided with one or more apertures 
located centrally of its length for attachment to the underside of top cap 
88 as at 150. The attachment is made by any suitable means such as one or 
more screws passing through one or more apertures in the leaf spring 
assembly and into a corresponding tapped hole or holes in top cap 88. 
Spacers may or may not be used, as required. 
The lower half-set 132 comprises a total of six rollers 138. Two of these 
rollers are in the rear and mounted on an axle 156 which is below axle 
140. The remaining four rollers of the lower half-set are arranged in 
pairs on respective axles 158, 160. 
The rear axle 156 is mounted on a yoke which is securely fastened to a 
ledge 162 of base plate 84. The two forward axles 158, 160 are on a yoke 
164 which is capable of a certain amount of adjustment. 
A pair of holes are provided in the bottom surface of yoke 164 and the 
distal ends of a corresponding pair of screws 166 pass into these holes. 
Details of each screw 166 are shown in FIG. 11. The distal end of the 
screw is rounded at 168 to provide a bearing surface on which the 
frusto-conically tapered end of the corresponding yoke hole seats. The 
screws are threaded into tapped holes in base plate 84 so that each screw 
is capable of being vertically adjusted. In this way it is possible to 
vertically position the forward set of four rollers. Once a desired 
adjustment has been obtained, the screws are locked by means of jam nuts 
170. The screws and jam nuts are accessible via suitable tools (not shown) 
which are introduced into a recess 172 to obtain the access. After 
adjustment and locking of the screws, recess 172 may be closed by a 
suitable plug 172a. 
Thus, the upper half-set 134 comprises four rollers which exert downward 
forces on the carriage at spaced apart points, and the lower half-set 132 
provides subjacent support. The top cap is shaped on its interior face to 
accommodate the upper half-set of rollers. The magnitude of the 
spring-loading is a function of the leaf spring characteristics and the 
amount of deflection thereof. Specific details of any given construction 
will depend upon the cutting loads anticipated, with the spring force 
being sufficient to prevent load-induced deflections. It is contemplated 
that a leaf spring assembly may comprise single or multiple leaves. 
This arrangement provides a secure mounting of the carriage on the head, 
for guidance and load reaction purposes, yet allows the carriage to 
reciprocate axially along the axis with minimal resistance. 
The horizontal set of rollers is analogous to the vertical set in that it 
comprises two half-sets, one to each horizontal side of carriage 128. As 
viewed in FIG. 10, one half-set 174 is to the right side, and the other 
half-set 176 is to the left side. 
The half-set 174 is analogous to the lower half-set 132 just described and 
the half-set 176 is analogous to the upper half-set 134. Each of the ten 
rollers in the horizontal set is identified by the reference numeral 178. 
They are arranged such that there are six rollers 178 in half-set 174 and 
four rollers 178 in the half-set 176. The six rollers of half-set 174 are 
arranged in exactly the same manner as the six rollers 138 of the lower 
half-set 132; in other words, one pair are on a yoke at the rear and the 
other two pairs on a forward yoke. The forward pairs are laterally 
positionable relative to the carriage axis in the same manner as yoke 164 
is vertically positionable. The two screws and jam nuts for laterally 
positioning the two forward pairs of rollers of half-set 174 are 
designated by the reference numerals 182 and 184 respectively. After the 
appropriate adjustments and locking have been made, access is prohibited 
by a cover plate 186 attached to the outside of base plate 84. (FIG. 9). 
The half-set 176 is spring-loaded in the same manner as the upper half-set 
134, comprising a leaf spring assembly 188 attached centrally of its 
length to the side wall 94 of base plate 84. With this arrangement, the 
horizontal set confines carriage 128 horizontally for guidance and load 
reaction purposes, yet allows the carriage to reciprocate axially with 
minimal resistance. 
A protective bellows 190 serves to seal the interior of the head around the 
carriage in the area where cutting activity takes place. The bellows 
comprises a smaller four-sided aperture at its forward end which fits in a 
sealed manner around the forward end of carriage 128 and extends 
rearwardly to a layer fourside rear aperture which attaches via a mounting 
ring 192 to the front of head 84 in a sealed manner. The bellows is 
constructed from a sturdy and durable material for protective purposes, 
yet it has sufficient flexibility that it imposes no significant 
restriction in the translation of the carriage on the head. 
Further details of linear motor 72 will now be described. A layer of copper 
204 is applied onto the outside of hub 118 and a soft copper ring 206 
located as shown at the joint between frame 102 and end plate 116. Magnet 
114 is polarized to issue a magnetic flux which passes through free space 
120. A very uniform magnetic field is created in the free space 120, and 
it is within this free space that an electric coil 200 of coil assembly 
100 is disposed. 
Coil assembly 100 may comprise a suitable slot 202 within which the coil is 
securely disposed. The coil is energized with an electric current and 
depending upon the magnitude of this electric current, there will be a 
certain degree of interaction between the magnetic field created by magnet 
114 in free space 120 and the magnetic field created by the electric 
current flowing in the coil. The consequence is that an axial force is 
applied to the coil, and hence also exerted on the entire coil assembly 
and carriage. This force is effective to selectively position the carriage 
with the positioning being a function of the magnitude of the current 
introduced into coil 200. In other words, by controlling the current in 
coil 200, the motion of carriage 128 is also controlled, and in the 
present invention the reciprocation of the cutting tool is therefore 
controlled by control of the current in coil 200. Wires from coil 200 
extend to a plug 203 via which a connection is made to the control. 
The two sensors 74 and 76 associated with linear motor 72 are also 
contained within the interior of head 82. The LVT sensor 76 is embodied as 
a coil 208 disposed on a tube 210 which is inserted coaxially through a 
suitable hole in end plate 116 and hub 118. The hole in the end plate and 
hub may be larger than the OD of the tube and coil and therefore bushings 
212 may be used at the ends to securely support the tube. A core 214 is 
disposed within tube 210 and is connected by a rod 216 to cap 126. 
Reciprocation of carriage 128 by linear motor 72 causes a similar 
reciprocation of core 214 within tube 210. This develops a signal in coil 
208 corresponding to the instantaneous velocity and the coil is connected 
via lead wires to a plug 218 via which a connection is made to the 
control. 
The LPT sensor 74 is located more forwardly. This sensor is a high 
precision device capable of very fine resolution. An example of such a 
device is a Heidenhaim sensor. It comprises a scale 220, in the form of a 
grating, attached to carriage 128, and a sensing head 222, fixedly mounted 
within head 82 in confrontation with scale 220. Lead wires extend from 
sensing head 222 to a plug 224 which delivers the LPT signal to control 
80. 
There are two additional sensors also located within the head. One sensor 
is a home sensor for establishing a home position for the carriage, and 
the other is an on-scale sensor for sensing when the scale 220 is active 
on the sensing head 222. (These are portrayed schematically in FIG. 12C, 
to be described later). 
The range of travel of carriage 128 on the head is greater than the limited 
range within which complex turning operations are conducted. Hence the 
precision LPT sensor 74 is active only over a limited extent of the total 
possible range of travel of the carriage. 
At the beginning of a turning operation, the carriage is extended forwardly 
from the home position to a position where actual cutting takes place. In 
this regard it can be appreciated that the home sensor and the on scale 
sensor provide the appropriate control functions whereby the carriage may 
rapid advance from the home position until it comes on scale at which time 
sensor 74 assumes control and precision turning operations are conducted. 
At the conclusion of the precision turning operations, the carriage can 
rapidly retract to the home position. 
The range of travel of the carriage is limited by crash stops 230 and 232. 
These crash stops are arranged within head 82 to act on cap 126. A spacer 
member 234 is attached between frame 102 and the rear end wall of top cap 
88. Crash stop 230 is attached within head 82 where the interior of spacer 
member 234 abuts the end surface of top cap 88. 
The other crash stop 232 is in the form of a circular annular member 236 
mounted on the forward end of hub 118 concentrically with the axis. The 
rod 216 which connects from cap 126 to core 214 passes centrally through 
crash stop 232. The rearward travel of the carriage is limited by abutment 
of the rear axial face of cap 126 with crash stop 232, and forward travel 
by abutment of the chamfer at the forward perimeter of cap 126 with crash 
stop 230. The purpose of the crash stops is to prevent undesirable 
overtravel of the carriage, and in the usual machining operations they do 
not come into play. Rather they come into play such as when improper 
control is introduced into coil 200 which otherwise would cause undesired, 
and potentially damaging, overtravel. 
All three plugs, 203, 218, and 224 are mounted in top cover 90, and each 
mates with a corresponding connector via which circuit connection is made 
to the control. 
The top cover is a formed part attached by screws so as to be conveniently 
removable for access to the interior of the head at the rear. The 
remainder of the head structure is constructed of sturdy parts to support 
the carriage and voice coil motor. 
In use, head 82 is enclosed. It may be desirable to provide a certain air 
circulation within the interior but without introducing any undesired 
contamination. This can be done by means of an inlet and outlet port (not 
shown) for example through baseplate 92, with filtered air being the 
medium circulated. The various component parts are assembled together in a 
conventional manner to construct the head. After assembly, adjustment of 
the rollers will typically be required to insure that the carriage motion 
follows the intended path. For alignment of the carriage on the head a 
pair of holes 242, 244 are provided, and these may be used to attach 
indicators or other pieces of equipment which are used to perform the 
alignment. Once the desired alignment has been obtained by the adjustment 
of the rollers, the adjustment screws are locked in place by the jam nuts. 
Because of concern about the mass of the carriage and those parts which 
move with the carriage, they are made of strong light-weight materials, 
such as titanium. In order to obtain the best possible characteristics for 
the magnetic field, magnet 114 is constructed from an exotic alloy such as 
samarium cobalt. 
During turning operations, the current in coil 200 is controlled in such a 
way as to create the desired oscillatory motion of the carriage and 
cutting tool. Hence the control current in the coil will contain an 
oscillatory component corresponding to the oscillatory motion desired. 
Exactly how this oscillatory current is developed can be better understood 
for consideration of FIGS. 12A, 12B and 12C and the ensuing description. 
FIGS. 12A, 12B, and 12C should be considered together and constitute a more 
detailed schematic diagram. Looking first to FIG. 12C, the reader will 
observe that linear motor 72 and sensors 74 and 76 are schematically 
portrayed. Also schematically portrayed are the home sensor and on-scale 
sensor previously referred to and now identified by the respective 
reference numerals 302 and 304. These two sensors have respective 
amplifiers 306 and 308, and an amplifier 310 is also associated with LVT 
sensor 76. These components just described are all contained within head 
82. Their operative coupling with control 80 is via plugs 203, 218 and 
224. 
Wires 312 and 314 serve to connect linear motor 72 with control 80. Wires 
316, 318, 320, 322, 324, and 326 connect the various sensors with the 
control. Control 80 contains a relay rack portion 328 and an electronic 
portion 329. Some of the wires from head 84 connect to devices in relay 
rack 328 while others pass through to the electronic portion 329. 
Relay rack 328 contains a control unit 330 and a power amplifier 332 both 
of which are associated with linear motor 72. Control unit 330 comprises a 
relay coil 334 controlling a moveable contact 336. Wire 312 connects to 
moveable contact 336 and the contact is controlled by coil 334 in the 
following manner. 
In one condition of coil 334, the contact 336 is connected (as shown) to a 
wire 338 leading from power amplifier 332. In other words in this 
condition of coil 334, power amplifier 332 controls linear motor 72. 
When coil 334 is operated to another condition, contact 336 is moved to 
connect wire 312 to another wire 340 leading to a voltage reference V. In 
this condition, the voltage V controls linear motor 72, causing tool 
retraction. 
Wires 342 and 344 extend from control unit 330 and power amplifier 332 
respectively. Wire 342 connects to a wire 346 from a motor overcurrent 
processor command 348. The motor overcurrent processor command 348 
controls the condition of coil 334 and hence controls whether the motor is 
being operated by power amplifier 332. or by the voltage V. 
Wire 344 connects to a wire 350 via which a command signal is supplied to 
power amplifier 332. When power amplifier 332 is connected to motor 72 by 
contact 336 being in the condition shown in FIG. 12C, the command signal 
supplied by wire 350 controls the motor. The connection of the power 
amplifier and control unit to the wires 346 and 350 is via a connector and 
plug 352 which is shown to provide additional connections for other wires 
between relay rack portion 328 and the electronics portion 329. 
Relay rack portion 328 also contains a multiplier 354 which is 
cooperatively associated with sensor 74. The three wires 318, 320, and 322 
are inputs to multiplier 354 and there are three output wires 356, 358, 
360 from multiplier 354. These latter wires connect through connector and 
plug 352 to respective wires 362, 364, 366. 
Sensor 74 provides output signals on the lines 318, 320 and 322 as the 
scale moves past the sensing head. Lines 318 and 322 deliver respective 
squarewaves which are phased 90 degrees apart from each other. As can be 
appreciated, the frequency of the two signals is related to the velocity 
of movement and because of the mathematical relationship of distance to 
velocity position information is also provided. By including the relative 
90 degree phasing, the two signals delivered by lines 318 and 322 also 
contain directional information. 
The signal delivered via channel 320 is a reference position marker signal 
representing a predetermined location along the scale. This location is 
used as an absolute reference position. 
Multiplier 354 acts upon the signals to enhance the resolution. Multiplier 
354 is a standard device which is manufactured also by the same company 
that manufactures sensor 74. 
Wires 368 and 370 are connected via connector and plug 352 with the 
respective wires 324 and 326. 
Thus FIG. 12C generally relates the earlier description of the associated 
components with the generalized block diagram of FIG. 7. Attention can now 
be focused on further details of control 80 with reference to FIGS. 12A 
and 12B. 
In FIG. 12A a multibus 380 interfaces control 80 with the CNC 58 via high 
speed data link 82. Multibus 380 serves a number of devices in control 80 
which are illustrated generally to comprise data receivers 382, address 
decoding 384 and control 386. The inputs to multibus 380 are in digital 
form and collectively define data information, address information, and 
control information. For example, the data information represents x-axis 
position information to command positioning of the carriage; address 
information identifies particular devices within control 80 which are to 
receive the data information or control information; and control 
information in conjunction with address information controls the flow of 
data information within control 80, or control information can issue 
direct commands to certain devices. A block labeled command latch 388 can 
latch data. It will be appreciated that these devices have been generally 
portrayed in FIG. 12A and that in the actual implementation of a control, 
there are specific lines connecting the various devices so that the inputs 
received on multibus 380 are properly utilized. 
Still referring to FIG. 12A, it will now be explained how x-axis control of 
the carriage is accomplished. Input data representing tool x-axis position 
commands is input to a position buffer latch 400. Position buffer latch 
400 in turn connects to a current position latch 402 which itself in turn 
connects to a prior position latch 404. In operation, the flow of input 
data is sequentially from latch 400 to latch 402 to latch 404. In other 
words data is sequentially moved from a preceding latch to a succeeding 
latch. The rate is a function of the speed at which the piston is being 
turned and the value of n. If it is assumed that n=360 and the piston 
turning speed is 40 r.p.s., then the rate of data flow is 14400 hz. Thus 
the latches 400, 402, 404 may be considered to form a channel with the 
output of latch 404 providing an instantaneous demand position in digital 
form. 
A digital-to-analog converter (DAC) 406 converts the digital demand 
position into an analog one. This is supplied as an input to a summing 
junction 408. For convenience the instantaneous demand position will be 
designated x.sub.i. 
A gate 410 receives two inputs entitled "Processor" and "Interrupt". The 
output of the gate in turn connects to latches 402, 404. Under normal 
turning operations, data passes sequentially through the channel in the 
manner just described. However certain conditions may call for 
interruption and this is done by the actuation of gate 410 acting upon the 
latches 402, 404. 
The processor and interrupt signals represent control signals received from 
the CNC 58 and/or control panel 78. 
The output of latch 402 is supplied to one input of a digital subtract 
circuit 412 while the output of latch 404 is supplied to the other input 
of the digital subtract circuit. The digital subtract circuit subtracts 
the two signals to yield an output signal corresponding to the difference 
between the current position and the prior position as registered by the 
two latches 402, 404. At any instant of time the output of digital 
subtract circuit 412 represents the size of the next increment of x-axis 
motion to be commanded. 
The output of circuit 412 is supplied as an input to a DAC 416. A reference 
input to DAC 416 is supplied from a second DAC 414, and this second DAC 
receives certain data. The output signal from DAC 416 is supplied both to 
an integrator 418 and to a circuit 420. The integrator output is connected 
to a second input of summing junction 408. The output of circuit 420 is 
connected to an input of a further summing junction 422 (see FIG. 12B). 
The output of summing junction 408 is also an input to summing junction 
422. 
The circuit containing integrator 418 is selectively used depending upon 
certain conditions. Basically, when used, it is intended to perform a 
smoothing function whereby the output of summing junction 408 may be 
considered to constitute a demand position "smoothed" which will result in 
smoother motion of the carriage. 
Circuit 420 performs the transfer function sK.sub.2 on x.sub.i, s being the 
well-recognized symbol for the Laplace operator used in mathematical 
description of servomechanisms. 
Circuit 420 provides a feed-forward signal to enhance the response of the 
carriage to the basic demand position. The basic demand position is 
transmitted from latch 404 to DAC 406 which in turn connects through 
summing junction 408 onto summing junction 422. Position feedback is 
subtracted at summing junction 422, and how the position feedback is 
developed will be explained later. 
DAC 406 has a gain K.sub.i acting on x.sub.i. Therefore, assuming that 
integrator 418 is inactive, the input signal to summing junction 422 is 
(K.sub.i +sK.sub.2)x.sub.i. It is from this signal that the position 
feedback signal is subtracted at summing junction 422 to produce a 
position error signal used to control linear motor 72. How the position 
feedback signal is developed will now be explained. 
Multiplier circuit 354 connects to receivers 424 via lines 362, 364, 366. 
An output line 426 from receivers 424 is an input to a fiduciary up/down 
counter 428. Two other lines 430 and 432 from receivers 424 are inputs to 
a direction logic circuit 434. Line 432 also connects to an input of 
counter 428. An output line 436 of direction logic circuit 434 is returned 
to another input of counter 428. 
The fiduciary up/down counter 428 is intended to set an absolute reference 
point which is called zero reference. The zero reference is set by 
response to the marker signal developed on line 358 and transmitted to 
line 364, as explained earlier. When the marker occurs, fiduciary up/down 
counter circuit 428 is enabled to begin counting from zero with the count 
being a measurement of the travel of the carriage from the reference zero. 
The direction logic 434 provides the proper direction of counting so that 
the counter faithfully follows the carriage travel in both directions 
along the x-axis. Because the marker constitutes an absolute reference on 
the machine, the control is now related to the absolute reference. 
A cutting start position register 440 is preloaded with data constituting 
an absolute position at which turning operations are to commence. It will 
be appreciated that this preload will typically be set to take into 
account the expected size of the part before turning so that the 
commencement of turning operations is slightly off the part to avoid the 
cutting tool inadvertently plunging into the part. 
The cutting start position data in register 440 is compared with the 
instantaneous position registered in fiduciary up/down counter 428 by a 
compare circuit 442. The compare circuit has an output line 444 which 
causes a cutting up/down counter 446 to begin to follow the carriage 
travel once the carriage has traversed the offset preloaded in register 
440. Counter 446 thereby takes into account the offset which has been 
preloaded in the cutting start position register 440 relative to the 
absolute reference of counter 428. 
The outputs from the two counters 428 and 446 are supplied respectively to 
latch circuits 452 and 454 respectively. The latch circuits provide 
information on the multibus which is made available to the CNC. 
Since the output of counter 446 represents the travel of the carriage from 
the cutting start position, it can be used to provide position feedback 
information for the closed loop control. This position feedback is 
designated in the FIG. 12B as x.sub.0 and is supplied to a DAC 456 which 
has a gain K.sub.p. The output from DAC 456 is an analog measurement of 
the instantaneous carriage position as measured from the offset. This 
information is processed by a circuit 458 which imposes the transfer 
function 
EQU 1/1+sT 
on it, and in turn connects to one input of a summing junction 460. 
Velocity feedback from sensor 76 and its amplifier 310 is transmitted 
through an amplifier 462 to a circuit 464 which imposes the transfer 
function 
EQU 1/1+sT 
on it. The resulting signal is also supplied to a summing junction 460. The 
sum of the two input signals to summing junction 460 is subtracted at 
summing junction 422 from K.sub.i x.sub.i to close the position feedback 
loop. Hence although the position feedback is composed principally of 
position information, it contains a component of velocity information 
also. 
The error signal from summing junction 422 is supplied through a contact 
450 to a further summing junction 466. Contact 450 is controlled by a 
device 448, and in this regard both device 448 and 450 could be 
solid-state, as well as the electromechanical depiction of the drawing. 
Device 448 is activated by the enablement of counter 446, and when 
activated it causes contact 450 to provide continuity from summing 
junction 422 to summing junction 466. This represents the commencement of 
closed-loop position control at the beginning of turning operations. 
The velocity feedback from amplifier 462 is also supplied to the 
subtraction input of summing junction 466 and the output of the summing 
junction is an error signal supplied to an amplifier 468. It is this 
amplifier 468 which in turn supplies the command to power amplifier 332. 
It is at summing junction 422 that the position error signal is created by 
subtracting the signal from summing junction 460 from the signal from 
summing junction 408. Assuming that the integrator 418 is inactive, the 
demand position to summing junction 422 is the sum of the signal K.sub.i 
x.sub.i from DAC 406 and the signal sx.sub.i K.sub.2 from circuit 420, as 
noted above. 
The feedback signal subtracted from the demand signal at summing junction 
422 equals: 
##EQU1## 
where 
K.sub.p represents the position feedback gain, 
K.sub.v represents the velocity feedback gain, and 
x.sub.0 =v/s, where v represents the instantaneous velocity. 
The position error signal is caused to satisfy the following condition: 
##EQU2## 
A particularly advantageous relationship is obtained by choosing the 
parameter T such that the following relationship is satisfied: 
EQU T=K.sub.v /K.sub.p, 
and by also setting 
EQU K.sub.2 /K.sub.i =K.sub.v2 /K.sub.p0. 
The selection of the individual circuit components to satisfy these 
relationships is accomplished through the practice of conventional design 
techaniques used in electronic and servomechanism design. 
When switch 450 is in the position which couples the output of summing 
junction 422 to the input of summing junction 466, the control assumes the 
position control mode of operation and it is this mode which is used 
during precision turning operations on a part. 
From consideration of the foregoing description and the drawings, it will 
be further appreciated that in the position control mode of operation, the 
minor feedback loop providing velocity feedback is also active to modify 
the position error signal. This modification occurs at summing junction 
466 and creates an error signal input to amplifier 468 which in turn acts 
upon power supply 332 to effect corresponding control of linear motor 72. 
During an operating sequence on a part, the position control mode of 
operation may be active for only a portion of the time. A typical 
operating sequence involves the carriage advancing from a home, or 
retracted, position toward a part with the actual turning operations being 
allowed to commence only after the cutting tool has been brought into 
close proximity with the part. 
Over the range of carriage advance from the home position to a position 
just off the part, the control operates in the velocity control mode where 
only the velocity feedback loop is active. 
In the velocity control mode, switch 450 is operated to conduct a demand 
velocity signal received from the CNC and converted into an analog signal 
by a DAC 470 to summing junction 466. The demand velocity is set by the 
particular part program. The part program also sets the cutting start 
position register with data representing offset, or the point at which the 
position control mode of operation is to commence. 
As the tool and carriage advance toward the part while the control is in 
the velocity control mode of operation, the reference marker is issued by 
position sensor 74 to set the absolute reference point into the control. 
The velocity control mode will continue until the offset, if any, has been 
traversed. 
Once the offset has been traversed, the position control mode begins at 
which time the up/down cutting counter 446 becomes active, and the 
contacts 450 are switched to conduct the signal from summing junction 422, 
instead of the signal from DAC 470, to summing junction 466. 
The position data received from the CNC control and acted upon by control 
80 causes input position commands to be issued to effect the closed loop 
position control of linear motor 72 and hence of the carriage and tool. In 
this regard the position commands are correlated with the rotation of the 
piston as provided by position encoder 54, and therefore the tool is 
caused to follow a path such as described above for example with reference 
to FIG. 4 where in turning an elliptical contour the carriage is caused to 
execute two oscillations per each revolution of the piston. The control 
operates to ensure the faithful correspondence of the cutting tool to the 
demand position so that the desired contour is imparted to the piston 
skirt. The process continues until the program has been executed at which 
time the carriage can be retracted to the home position. 
The turning operations are conducted with efficiency and accuracy. The 
interaction between the control electronics and the mechanical mechanism 
achieves a response which enables the tool tip to closely track the 
desired contour to be created in the part while the part is rotating at 
relatively high speed. Moreover, this is accomplished without undesired 
deflections, tool chatter or like impediments to the machine's 
performance, and the mechanical construction of the head in conjunction 
with the linear motor are especially advantageous in enabling this 
outstanding performance to be attained. 
While the advantageous aspects of the invention are most readily apparent 
when the tool is performing the finish operations because this is where 
the final accuracy is imparted to the piston, the invention can be used to 
conduct operations other than finish turning. For example, by appropriate 
programming of the CNC it is possible for the tool to conduct semifinish 
turning, grooving, and other related operations, in addition to finish 
turning. Therefore, a turning machine embodying principles of the 
invention is adapted to conduct all the necessary operations which are 
required in turning of a part such as a piston. Because these operations 
may be defined mathematically by the computer program entered into the 
CNC, significant accuracies and improvements in efficiencies result while 
at the same time the machine is endowed with versatility to produce parts 
of different geometrical requirements without any significant changeover. 
The CNC is a conventional apparatus which is programmed in a conventional 
manner to cause the control to execute the above defined functions. In 
this regard conventional programming techniques are employed to create an 
operating program based on knowledge of the part geometry and the 
organization and arrangenent of the turning apparatus. The CNC can perform 
the necessary calculations on a realtime basis to provide signals via high 
speed data link 82 to control 80. For example as noted above, 14,400 hertz 
may be a typical frequency of position data transmission, and for the 
typical geometries involved, the mechanism can faithfully follow inputs at 
this rate. 
A turning machine embodying principles of the invention exhibits a 
performance which enables the cutting tool to follow, with quickness and 
accuracy, changes which are correlated with the rapidly rotating part 
being turned. Depending upon the actual profile of a part, any given 
updating from the CNC may or may not contain a change in position 
information. For example, in the case where a circular shape is to be 
created in conjunction with an axial taper, the radial position of the 
cutting tool would change at most only once per revolution of the piston, 
and therefore the updating of the demand position would actually change at 
most only once per revolution of the part. 
The versatility of the invention should be readily apparent. In order to 
change the machine to turn a different piston shape, all that is necessary 
is to load the CNC with a new program relating to the new piston geometry. 
The CNC will act upon the program in conjunction with the feedback signal 
from encoder 54 to provide appropriate command signals for the radial 
positioning of the cutting tool. The closed loop control as disclosed with 
reference to FIGS. 12A, 12B, and 12C comprises means for enabling the tool 
to faithfully follow the commands. 
It will also be observed that the mechanical construction of the turning 
machine has the advantage of being relatively compact, yet possessing 
strength to conduct the turning operations in conjunction with the ability 
to respond quickly to even small changes. 
Based upon the foregoing description, it will be appreciated that details 
of the turning machine construction can be specified in accordance with 
conventional engineering design and fabrication procedures. For example 
the characteristics of the leaf spring mechanism are chosen to provide for 
the forceful constraint of the bar in the assembled condition of the 
machine as illustrated with reference to FIGS. 8, 9, and 10. The amount of 
force which is exerted is sufficient to prevent undesired deflections at 
all times, even tool chatter when the tool is operating on a workpiece in 
the usual manner. The extent of the yieldable forceful constraint is 
however insufficient to detract in any significant way from the ability of 
the carriage to roll fully on the sets of rollers. Although the engagement 
of the rollers with the bar is described as being yieldably forceful, the 
typical usage of the turning machine under the intended operating 
conditions does not result in yielding of the rollers. 
It is also to be observed that the action of the rollers on the carriage is 
symmetrical so that no undesired bending loads are created in the carriage 
by virtue of the yieldably forceful action of the rollers upon it. By 
utilizing a bar of rectangular cross section for the carriage and two sets 
of orthogonally related (90.degree. apart) rollers acting upon the 
opposite parallel surfaces of the bar, the bar is accurately guided for 
straight line motion. With the adjustment feature provided for each of the 
two orthogonally related sets of rollers as described above, the line of 
travel can be accurately set in both a vertical plane as well as a 
horizontal one. 
It should also be observed that the rollers alone serve to guide and 
constrain the moving parts. In other words there is no guide means which 
is directly active on the armature of the linear motor. 
The invention comprises a significant development in turning apparatus, and 
while a preferred embodiment has been disclosed, it will be appreciated 
that principles are applicable to other embodiments.