Phase controller for motor

There is disclosed a phase controller comprising: a motor; a rotation detector for converting a motor rotating condition into a speed signal and a phase signal; a speed comparison circuit for detecting a difference between the speed signal and a speed target value; a resettable phase signal generating circuit for generating a phase reference signal; a phase comparison circuit for detecting a phase difference between the phase signal and the phase reference signal and outputting a reset signal to the phase signal generating circuit according to the output of the speed comparison circuit; a synthesizing circuit for synthesizing the output of the speed comparison circuit and the output of the phase comparision circuit; and a motor driving circuit for driving the motor according to the output of the synthesizing circuit. By resetting the phase reference signal according to the motor phase, the phase control pulling-in time is reduced to improve response.

FIELD OF THE INVENTION 
The present invention relates to a phase controller for a motor. 
DESCRIPTION OF THE PRIOR ART 
Phase control is usually necessary for the motors for which high precision 
rotation control is required such as a cylinder motor and a capstan motor, 
which are used for video tape recorders (hereinafter to be abbreviated as 
VTR) and digital audio tape recorders (hereinafter to be abbreviated as 
DAT). Description will be made on an example of conventional motor phase 
controller hereinbelow. 
The rotational speed of a motor is converted into an electric signal by a 
rotational speed detector and further converted into a voltage signal by a 
speed detecting circuit. The voltage signal from the speed detecting 
circuit is transferred through an adder to a direct current amplifier to 
drive the motor. In other words, a speed control is applied to the motor. 
On the other hand, the rotational phase of the motor is converted by a 
rotary phase detector into an electric signal and transferred through an 
amplifier to a phase detecting circuit. The phase detecting circuit 
converts a phase difference between the rotational phase signal amplified 
by the amplifier and a phase reference signal into a voltage signal, which 
is transferred through a compensation circuit to the adder. By these 
steps, the motor is subjected to a phase control with the phase reference 
signal. 
According to the constitution as above, however, the time required to 
pull-in the phase is determined by the response time of the phase control 
system, so that more rapid phase pulling-in is impossible. 
SUMMARY OF THE INVENTION 
An object of the present invention is to shorten the phase pull-in time in 
the phase control of motors as described above. 
In order to attain the above object, the present invention has a 
construction comprising: 
a motor to be subjected to control; 
a rotation detector for producing a speed signal and a phase signal of the 
motor; 
a speed comparison circuit for producing a speed difference signal between 
the speed signal from the rotation detector and a target value; 
a resettable phase signal generating circuit for producing a reference 
phase signal; 
a phase comparison circuit which produces a phase difference signal between 
the phase signal from the rotation detector and the reference phase signal 
from the phase signal generating circuit, and is responsive to the speed 
difference signal from the speed comparison circuit for outputting a reset 
signal to the phase signal generating circuit when the rotational speed of 
the motor is in a prescribed range; 
a synthesizing circuit for synthesizing the speed difference signal from 
the speed comparison circuit and the phase difference signal from the 
phase comparison circuit; and 
a motor driving circuit for driving the motor in response to an output of 
the synthesizing circuit. 
By means of the abovementioned construction it becomes possible to shorten 
the phase control pull-in time by resetting the reference phase signal in 
accordance with the phase of the motor. 
For example, there are such merits that, when the phase controller of the 
invention is used to control the cylinder motor of VTR or DAT, it becomes 
possible to pick up sound quickly after a transition from one mode to 
another, and when used to control the capstan motor of VTR or DAT, a 
continuous recording after a STOP or PLAY mode without track dislocation 
can be realized.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
FIG. 1 is a block diagram showing one embodiment of a phase controller for 
a motor according to the present invention. 
The rotational speed and the rotational phase of a motor 1 are detected by 
a rotation detector 2 and outputted as a speed signal and a phase signal, 
respectively. A speed comparison circuit 3 produces a speed difference 
signal by comparing the speed signal from the rotation detector 2 with a 
target value, and outputs it to a synthesizing circuit 6. A phase 
comparison circuit 4 detects a phase difference between the phase signal 
from the rotation detector 2 and a phase reference signal generated by a 
phase signal generating circuit 5, and outputs a phase difference signal 
to the synthesizing circuit 6. The phase comparison circuit 4 outputs also 
a reset signal for resetting the phase signal generating circuit 5 in 
response to the output of the speed comparison circuit 3. The synthesizing 
circuit 6 synthesizes the speed difference signal and the phase difference 
signal to produce a drive command signal. A motor driving circuit 7 drives 
the motor 1 in response to the drive command signal. 
FIG. 2 is one embodiment of detailed circuit construction of FIG. 1. 
The rotation detector 2 is constituted by a speed detector 20 for 
outputting pulses having a period proportional to the rotation cycle of 
the motor 1, a speed signal, and a phase detector 21 for outputting one 
pulse per one rotation cycle of the motor 1, a phase signal. 
The speed comparison circuit 3 is constituted by a timing generating 
circuit 8, a clock generating circuit 9, a counter circuit 10, and a latch 
circuit 11. 
The timing generation circuit 8 comprises a shift register circuit 22, AND 
circuits 23, 24, 25, and an RS flip-flop 26. The counter circuit 10 
comprises an initial value generating circuit 27, and AND circuit 28, and 
a counter circuit 29 with a load terminal. 
The shift register circuit 22 is operated by output clock (FIG. 3b) of the 
clock generating circuit 9 to shift the speed signal (FIG. 3a) from the 
speed detector 20 as shown in FIG. 3c and d. The AND circuits 23, 24 and 
25 produce a latch signal (FIG. 3e), a load signal (FIG. 3f) and a 
startsignal (FIG. 3g), respectively, from outputs of the shift register 
circuit 22. The RS flip-flop 26 is reset by the latch signal and set by 
the start signal. Accordingly, the output of the RS flip-flop 26 becomes 
as shown in FIG. 3h. 
When the speed signal becomes "H" (hereinafter, a high level of a signal is 
shown by "H", and a low level by "L"), the output of the RS flip-flop 26 
becomes "L", and the output of the AND circuit 28 receiving the clock from 
the clock generating circuit 9 also becomes "L", so that the counting 
operation of the counter circuit 29 is stopped. And, by the latch signal 
from the AND circuit 23, the count value of the counter circuit 29 is 
latched in the latch circuit 11. The counter circuit 29 loads an output 
value of the initial value generating circuit 27 by the load signal from 
the AND circuit 24. The RS flip-flop 26 is set by the start signal from 
the AND circuit 25, so that the counter circuit 29 again starts counting 
the output of the AND circuit 28. This state is shown in FIG. 3i. 
Accordingly, on each occasion of a pulse of the speed signal, the latch 
circuit 11 latches a value of the period of the speed signal counted by 
the output of the clock generating circuit 9. 
The phase comparison circuit 4 is constituted by a phase difference output 
circuit 82 and a reset signal output circuit 17. This phase difference 
output circuit 82 comprises a timing generating circuit 13, a clock 
generating circuit 14, a counter circuit 15, and a latch circuit 16. The 
reset signal output circuit 17 comprises limit circuits 39, 40 and a pulse 
generating circuit 41. The timing generating circuit 13 is constituted by 
shift register circuits 30, 31, AND circuits 32, 33, 34, and an RS 
flip-flop 35. 
The shift register circuit 30 is operated by output clock of the clock 
generating circuit 14 to shift the phase reference signal (FIG. 4a) from 
the phase signal generating circuit 5. Outputs (FIG. 4b, c) from the shift 
register circuit 30 is inputted into the AND circuit 32 whose output 
signal (FIG. 4d) sets the RS flip-flop 35. An output of the RS flip-flop 
35 is shown in FIG. 4e. The AND circuit 37 passes the output of the clock 
generating circuit 14 to the counter circuit 38 in response to the output 
of the flip-flop 35, so that the counter circuit 38 starts counting. The 
shift register circuit 31 is operated by the output clock of the clock 
generating circuit 14 to shift the phase signal (FIG. 4f) from the phase 
detector 21. The AND circuits 33, 34 produce the timing signals shown in 
FIGS. 4g and h, respectively, from outputs of the shift register circuit 
31. The output of the AND circuit 33 resets the RS flip-flop 35 to stop 
the clock of the counter circuit 38, and at the same time is inputted into 
the latch circuit 16 so that the latch circuit 16 latches the counting 
value of the counter circuit 38. And, in response to the output of the AND 
circuit 34, an initial value from the initial value generating circuit 36 
is loaded on the counter circuit 38. Accordingly, the latch circuit 16 
latches a phase difference signal corresponding to a phase difference 
between the phase reference signal and the phase signal and outputs the 
phase difference signal to the synthesizing circuit 6 and the limit 
circuit 40. 
The limit circuit 39 is composed of comparator circuits 42, 43 each of 
which compares the values of the signals at its two input terminals DA and 
DB and outputs an "H" level signal when the signal at DA is larger than 
that at DB, a reference value generating circuit 44, and an AND circuit 
45. The reference value generating circuit 44 outputs a lower limit value 
to the DB terminal of the comparator circuit 42 and an upper limit value 
to the DA terminal of the comparator circuit 43. The output of the speed 
comparison circuit 3 is inputted into the DA terminal of the comparator 
circuit 42 and the DB terminal of the comparator circuit 43, and compared 
with the lower limit value and the upper limit value. An output of the AND 
circuit 45 which receives outputs of the comparator circuits 42 and 43 
becomes "H" if the value of the output of the speed comparison circuit 3 
is between the lower limit value and the upper limit value. 
The limit circuit 40 is constituted by comparator circuits 46, 47 similar 
to the abovementioned comparator circuits 42, 43, a reference value 
generating circuit 48, and an OR circuit 49. The reference value 
generating circuit 48 outputs a lower limit value to the DA terminal of 
the comparator circuit 46 and an upper limit value to the DB terminal of 
the comparator circuit 47. The output of the latch circuit 16 is inputted 
into the DB terminal of the comparator circuit 46 and the DA terminal of 
the comparator circuit 47, and compared with the lower limit value and the 
upper limit value. An output of the OR circuit 49 becomes "H" when the 
value of the output of the latch circuit 16 is smaller than the lower 
limit value or larger than the upper limit value. 
The pulse generating circuit 41 is constituted by a shift register circuit 
51 and an AND circuit 50. The shift register circuit 51 normally maintains 
its output NQ "H" because of its reset input being "L". When the output of 
the speed comparison circuit 3 is within the range set by the reference 
value generating circuit 44 and the output of the latch circuit 16 is 
within the range set by the reference value generating circuit 48, an 
output of the AND circuit 50 becomes "H" (FIG. 5f), and so that the shift 
register 51 starts its shift operation responsive to the output (FIG. 5d) 
of the AND circuit 33. As to the output of the shift register circuit 51, 
as shown in FIG. 5e, the output NQ becomes "L" at the second shift 
operation. The output NQ is applied as a reset signal to the phase signal 
generating circuit 5, and through the AND circuit 50 to the reset terminal 
of the shift register circuit 51. 
The phase signal generating circuit 5 is constituted by an oscillation 
circuit 18 and a frequency dividing circuit 19 with a reset terminal. An 
output (FIG. 5b) of the oscillation circuit 18 is divided by the frequency 
dividing circuit 19 and the divided signal is outputted as a phase 
reference signal (FIG. 5c). The phase reference signal from the frequency 
dividing circuit 19 after receiving the reset signal at its reset terminal 
is so set that the phase relationship, immediately after receipt of the 
reset signal, between the phase signal of the motor 1 and the phase 
reference signal becomes a target value of the phase control. 
The output of the speed comparison circuit 3 and the output of the phase 
comparison circuit 4 are synthesized in the synthesizing circuit 6. 
According to the synthesized output from the synthesizing circuit 6, the 
motor driving circuit 7 drives the motor 1. 
Accordingly, with the above embodiment, when the motor 1 changes from the 
stopped state or from a state of rotating at a certain speed to the phase 
controlled state to rotate at a prescribed speed, the pulling-in of the 
speed control is detected by the limit circuit 39, the state that the 
phase control is released is detected by the limit circuit 40, and the 
phase reference signal of the phase signal generating circuit is reset 
according to the phase signal of the motor 1. Therefore, the phase 
pulling-in is instantaneously completed. 
Although the count number of the shift register circuit 51 is set as 2, 
this number may be arbitrarily set according to the response of the phase 
system. 
The above embodiment can be effectively applied for example to the control 
of the cylinder motor of VTR or DAT. 
FIG. 6 is the second embodiment of the detailed circuit constitution of 
FIG. 1, and the description of the parts identical with those of FIG. 2 is 
omitted. 
The rotation detector 2 is constituted by a speed detector 73 which outputs 
a signal having a period proportional to the rotating cycle of the motor 1 
as a speed signal, and a frequency dividing circuit 74 which divides the 
output of the speed detecor 73 and outputs the divided signal as a phase 
signal. 
The phase comparison circuit 4 comprises a timing generating circuit 52, a 
limit circuit 53 for detecting whether the output of the speed comparison 
circuit 3 is within a prescribed range or not, a reset signal generating 
circuit 54, and a latch circuit 55. 
The timing generating circuit 52 is constituted by an oscillating circuit 
56, a shift register circuit 57, and an AND circuit 58. 
The limit circuit 53 is constituted by comparator circuits 60, 61 each of 
which compares the values of the signals inputted thereto at its two input 
terminals DA and DB respectively and outputs "H" (high level signal) when 
the signal at DA is larger than that at DB, a reference value generating 
circuit 59, and an AND circuit 62. As its operation is equal to that of 
the aforementioned limit circuit 39, description is omitted. 
The reset signal generating circuit 54 is constituted by an RS flip-flop 
circuit 83 which outputs "L" in response to a phase control initiating 
signal and "H" in response to a phase control stopping signal, and an AND 
circuit 63. In VTR or DAT, during the PLAY mode, a phase control is 
exerted to the motor by using a signal reproduced from a recording tape, 
but during the REC (RECORD) mode in which there is no reproduced signal, 
it is necessary to apply a phase control according to the output of the 
rotation detector of the motor. This embodiment is designed to effect the 
latter phase control to perform quick phase pulling-in, for example, in 
case of a shift from the stopping mode to the REC mode (by pressing a REC 
switch) or in case of a shift from the PLAY mode to the REC mode (by 
pressing a continuous recording switch), it is intended to complete 
promptly the phase pulling-in. The phase control initiating signal and the 
phase control stopping signal are control signals for the phase control 
using the output of the rotation detector of the motor. These two phase 
control signals may be produced by a system controller (not shown) for 
controlling the whole system of VTR or DAT. Alternatively, the phase 
control initiating signal may be a switch operation detecting signal of 
the REC or continuous recording switch (not shown), and the phase control 
stopping signal may be a switch operation detecting signal of the STOP 
switch (not shown). 
The phase signal generating circuit 5 is constituted by an oscillating 
circuit 66 which oscillates at a specific frequency, an initial value 
generating circuit 64, and a counter circuit 65 which loads an output of 
the initial value generating circuit 64 in response to a reset signal from 
the reset signal generating circuit 54 and starts counting the output 
clock of the oscillation circuit 66. 
The shift register circuit 57 shifts the phase signal (FIG. 7a) in response 
to the output clock of the oscillation circuit 56. Output of the shift 
register circuit 57 is shown in FIGS. 7b, c. The AND circuit 58 outputs a 
timing signal as shown in FIG. 7d according to the output of the shift 
register circuit 57. 
The limit circuit 53 outputs an "H" level signal when the output value of 
the speed comparison circuit 3 is between an upper limit value and a lower 
limit value set by the reference value generating circuit 59. 
The shift to the phase control state based on the output of the rotation 
detector takes place in response to the phase control initiating signal. 
First, before an input of the phase control initiating signal, i.e., after 
an input of the phase control stopping signal, the output of the RS 
flip-flop circuit 83 is "H", and the AND circuit 63 outputs a reset signal 
as shown in FIG. 7f. The counter circuit 65 carries out counting the 
output clock of the oscillation circuit 66, in which the time for one 
circulation of the counter is equal to a reference cycle of the phase 
system. The count value of the counter circuit 65 when it is reset by the 
reset signal is set by the initial value generating circuit 64 to be the 
center value in the operation of the phase control. That is to say, when 
the phase control is not necessitated, in response to each input of the 
phase signal (FIG. 7a) the count value of the counter circuit 65 is set to 
the output value of the initial value generating circuit 64, and latched 
by the latch circuit 55, so that the output of the phase comparison 
circuit 4 becomes a constant value. The count value of the counter circuit 
65 is shown in FIG. 7g, and the output value of the latch circuit 55 is 
shown in FIG. 7h. 
When the phase control initiating signal (FIG. 7e) is inputted, the output 
of the RS flip-flop circuit 83 becomes "L", so that the reset signal which 
is the output of the AND circuit 63 becomes "L" and thereafter is kept "L" 
as shown in FIG. 7f. Accordingly, the counter circuit 65 does not load the 
output value of the initial value generating circuit 64 and continues 
counting the output clock of the oscillation circuit 66. The latch circuit 
55 latches the count value of the counter circuit 65 in response to the 
output of the AND circuit 58 (FIG. 7d) and outputs the latched value to 
the synthesizing circuit 6. This output value represents a phase 
difference from the one circulation cycle of the counter circuit 65. The 
condition of the counter circuit 65 is shown in FIG. 7g, and the output 
value of the latch circuit in FIG. 7h. 
Accordingly, in shifting to the phase control condition in response to the 
phase control initiating signal, pull-in to the center value of the 
counter circuit 65 is completed instantaneously. 
The output of the speed comparison circuit 3 and the output of the latch 
circuit 55 are added, subjected to pulse width modulation, and then passed 
through a low-pass filter circuit, in the synthesizing circuit 6. The 
construction and operation of this sequence are illustrated in detail 
hereinafter. 
The synthesizing circuit 6 is constituted by an adding circuit 67, a data 
identifying circuit 68, a timing generating circuit 69, a logical 
inverting circuit 70 for inverting pulse-width-modulated data, a 
synchronous counter circuit 71, and a low-pass filter circuit 72. 
The data identifying circuit 68 is constituted by latch circuits 73, 74 
responsive to an output signal of the timing generating circuit 69, and a 
comparison circuit 75 which compares latched values of the latch circuits 
73, 74 and outputs "L" when the values are different from each other. 
The output of the speed comparison circuit 3 and the output of the latch 
circuit 55 are added in the adding circuit 67, and the added value is 
inputted to the synchronous counter circuit 71 and the data identifying 
circuit 68. The output value of the adding circuit 67 is shown in FIG. 8a. 
In this embodiment, the data is assumed an 8 bit length data between `00`H 
(hexadecimal) and `FF`H. The data identifying circuit 68 outputs "L" when 
the output data of the adding circuit 67 is changed and "H" when the same 
is constant (FIG. 8b). The timing generation circuit 69 outputs a clock 
signal and a load signal as shown in FIG. 8c. In the embodiment of FIG. 6, 
due to the 8 bit length of data, the load signal is 2.sup.8 divisional 
frequency of the clock. The synchronous counter circuit 71 has at least 
8+1=9 bit length. The synchronous counter circuit 71 loads the output 
values of the adding circuit 67 in response to a load signal from a NAND 
circuit 77 as shown in FIG. 8d only when the output of the data 
identifying circuit 68 is "H", and counts, as shown in FIG. 8e, the clock 
output from the timing generating circuit 69. In this example the loaded 8 
bit data is `40`H (hexadecimal) as shown in FIG. 8 e. As an effective 
output of the synchronous center circuit 71 the bit-9 data of its count 
data is selected. This is shown in FIG. 8f. This output (FIG. 8f) is a 
pulse-width-modulated data of the data inputted to the synchronous counter 
circuit 71, and is applied to an EX-OR circuit 81. 
When the output of the data identifying circuit 68 is "L", the load signal 
is not inputted to the synchronous counter circuit 71, so that the 
synchronous counter circuit 71 continues its counting operation. On the 
other hand, since the output of the data identifying circuit 68 is applied 
through an inverter 76 to an AND circuit 78, the output of the AND circuit 
78 becomes "H", which is latched by a D flip-flop 79, so that an output 
logic of a T flip-flop 80 is inverted. This state is shown in FIG. 8g. As 
a result, as shown in FIG. 8h, the output of the EX-OR circuit 81 is 
inverted and the previous pulse width is retained. Therefore, the 
pulse-width-modulated output signal is not disturbed at the time of 
variation of the data. 
The pulse-width-modulated output signal from the EX-OR circuit 81 is 
converted to an analog signal by the low-pass filter circuit 72 and 
outputted to the driving circuit 7 to drive the motor 1. 
In the above-described embodiment, the bit number of the data inputted to 
the synchronous counter circuit 71 was set to be 8 bits. However, the bit 
number is to be determined by the data length of the output of the speed 
comparison circuit 3 and the phase comparison circuit 4, and it is not 
limitative. 
The embodiment shown in FIG. 6 can be effectively employed for controlling 
the capstan motor of VTR or DAT.